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usb:gadget:u_audio: Regression in [v3,3/3] usb: gadget: u_audio: add real feedback implementation - wMaxPacketSize calculation

Message ID f861e345-3642-5bfa-0ce7-a5cd34204613@ivitera.com
State New
Headers show
Series usb:gadget:u_audio: Regression in [v3,3/3] usb: gadget: u_audio: add real feedback implementation - wMaxPacketSize calculation | expand

Commit Message

Pavel Hofman July 13, 2021, 10:22 a.m. UTC
Hi,

I am testing the three Ruslan's async feedback patches as modified by 
Jerome and I hit a regression in windows 10 enumeration.

Ruslan posted an already accepted patch 
https://github.com/torvalds/linux/commit/789ea77310f0200c84002884ffd628e2baf3ad8a#diff-876615ece7fb56ce8d45fc70623bef9caa2548e810426f217fb785ffa10b33d5 
which allowed win10 enumeration.

Ruslan's async feedback patchset kept the change: 
https://patchwork.kernel.org/project/linux-usb/patch/1614603943-11668-5-git-send-email-ruslan.bilovol@gmail.com/

                                                     max_size_ep));


I do not know if this is the most correct solution but IMO a similar 
patch should be applied. I can send a proper patch mail if this solution 
is acceptable.

Thanks a lot,

Pavel.

Comments

Greg KH July 13, 2021, 10:49 a.m. UTC | #1
On Tue, Jul 13, 2021 at 12:22:38PM +0200, Pavel Hofman wrote:
> Hi,
> 
> I am testing the three Ruslan's async feedback patches as modified by Jerome
> and I hit a regression in windows 10 enumeration.
> 
> Ruslan posted an already accepted patch https://github.com/torvalds/linux/commit/789ea77310f0200c84002884ffd628e2baf3ad8a#diff-876615ece7fb56ce8d45fc70623bef9caa2548e810426f217fb785ffa10b33d5

We do not use github for kernel stuff, just reference the git commit id
properly and all is good.

> which allowed win10 enumeration.
> 
> Ruslan's async feedback patchset kept the change: https://patchwork.kernel.org/project/linux-usb/patch/1614603943-11668-5-git-send-email-ruslan.bilovol@gmail.com/

I do not understand this reference at all.


> 
> diff --git a/drivers/usb/gadget/function/f_uac2.c
> b/drivers/usb/gadget/function/f_uac2.c
> index 72b42f8..91b22fb 100644
> --- a/drivers/usb/gadget/function/f_uac2.c
> +++ b/drivers/usb/gadget/function/f_uac2.c
> @@ -506,6 +506,10 @@  static int set_ep_max_packet_size(const struct
> f_uac2_opts *uac2_opts,
> 
>  	max_size_bw = num_channels(chmask) * ssize *
>  		((srate / (factor / (1 << (ep_desc->bInterval - 1)))) + 1);
> +
> +	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))
> +		max_size_bw = max_size_bw * FBACK_FREQ_MAX / 100;
> +
>  	ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,
>  						    max_size_ep));
> 
> 
> Jerome's rebase patch which was accepted recently changed the functionality
> to the original code:
> https://patchwork.kernel.org/project/linux-usb/patch/20210603220104.1216001-4-jbrunet@baylibre.com/
> 
> diff --git a/drivers/usb/gadget/function/f_uac2.c
> b/drivers/usb/gadget/function/f_uac2.c
> index 321e6c05ba93..ae29ff2b2b68 100644
> --- a/drivers/usb/gadget/function/f_uac2.c
> +++ b/drivers/usb/gadget/function/f_uac2.c
> @@ -584,8 +584,11 @@  static int set_ep_max_packet_size(const struct
> f_uac2_opts *uac2_opts,
>  		ssize = uac2_opts->c_ssize;
>  	}
> 
> +	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))
> +		srate = srate * (1000 + uac2_opts->fb_max) / 1000;
> +
>  	max_size_bw = num_channels(chmask) * ssize *
> -		((srate / (factor / (1 << (ep_desc->bInterval - 1)))) + 1);
> +		DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1)));
>  	ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,
>  						    max_size_ep));
> 
> With this version my Win10 does not enumerate the USB AUDIO device, even if
> it has only EP-IN capability (i.e. is_playback = true). For my setup the
> EP-IN wMaxPacketSize is 192bytes vs. 196bytes in Ruslan's version, causing
> win10 reporting "The specified range could not be found in the range list."
> 
> A simple change makes Win10 enumerate both playback-only as well as duplex
> playback/capture async device:
> 
> diff --git a/drivers/usb/gadget/function/f_uac2.c
> b/drivers/usb/gadget/function/f_uac2.c
> index ae29ff2b2b68..5ba778814796 100644
> --- a/drivers/usb/gadget/function/f_uac2.c
> +++ b/drivers/usb/gadget/function/f_uac2.c
> @@ -588,7 +588,7 @@ static int set_ep_max_packet_size(const struct
> f_uac2_opts *uac2_opts,
>                 srate = srate * (1000 + uac2_opts->fb_max) / 1000;
> 
>         max_size_bw = num_channels(chmask) * ssize *
> -               DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval -
> 1)));
> +               (DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval -
> 1))) + 1);
>         ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,
>                                                     max_size_ep));
> 
> 
> I do not know if this is the most correct solution but IMO a similar patch
> should be applied. I can send a proper patch mail if this solution is
> acceptable.

Just send the patch and we will go from there.

thanks,

greg k-h
Felipe Balbi July 13, 2021, 12:32 p.m. UTC | #2
Hi,

Jerome Brunet <jbrunet@baylibre.com> writes:
>> I am testing the three Ruslan's async feedback patches as modified by
>> Jerome and I hit a regression in windows 10 enumeration.
>>
>> Ruslan posted an already accepted patch
>> https://github.com/torvalds/linux/commit/789ea77310f0200c84002884ffd628e2baf3ad8a#diff-876615ece7fb56ce8d45fc70623bef9caa2548e810426f217fb785ffa10b33d5 
>> which allowed win10 enumeration.
>>
>> Ruslan's async feedback patchset kept the change:
>> https://patchwork.kernel.org/project/linux-usb/patch/1614603943-11668-5-git-send-email-ruslan.bilovol@gmail.com/
>>
>> diff --git a/drivers/usb/gadget/function/f_uac2.c
>> b/drivers/usb/gadget/function/f_uac2.c
>> index 72b42f8..91b22fb 100644
>> --- a/drivers/usb/gadget/function/f_uac2.c
>> +++ b/drivers/usb/gadget/function/f_uac2.c
>> @@ -506,6 +506,10 @@  static int set_ep_max_packet_size(const struct
>> f_uac2_opts *uac2_opts,
>>
>>  	max_size_bw = num_channels(chmask) * ssize *
>>  		((srate / (factor / (1 << (ep_desc->bInterval - 1)))) + 1);
>> +
>> +	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))
>> +		max_size_bw = max_size_bw * FBACK_FREQ_MAX / 100;
>> +
>>  	ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,
>>  						    max_size_ep));
>>
>>
>> Jerome's rebase patch which was accepted recently changed the functionality
>> to the original code:
>> https://patchwork.kernel.org/project/linux-usb/patch/20210603220104.1216001-4-jbrunet@baylibre.com/
>>
>> diff --git a/drivers/usb/gadget/function/f_uac2.c
>> b/drivers/usb/gadget/function/f_uac2.c
>> index 321e6c05ba93..ae29ff2b2b68 100644
>> --- a/drivers/usb/gadget/function/f_uac2.c
>> +++ b/drivers/usb/gadget/function/f_uac2.c
>> @@ -584,8 +584,11 @@  static int set_ep_max_packet_size(const struct
>> f_uac2_opts *uac2_opts,
>>  		ssize = uac2_opts->c_ssize;
>>  	}
>>
>> +	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))
>> +		srate = srate * (1000 + uac2_opts->fb_max) / 1000;
>> +
>>  	max_size_bw = num_channels(chmask) * ssize *
>> -		((srate / (factor / (1 << (ep_desc->bInterval - 1)))) + 1);
>> +		DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1)));
>>  	ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,
>>  						    max_size_ep));
>>
>> With this version my Win10 does not enumerate the USB AUDIO device, even if
>> it has only EP-IN capability (i.e. is_playback = true). For my setup the
>> EP-IN wMaxPacketSize is 192bytes vs. 196bytes in Ruslan's version, causing
>> win10 reporting "The specified range could not be found in the range list."
>>
>
> Maybe I am lacking USB expertize, but is there any reason why a 192bytes
> maximum packet size should be considered invalid ? Just from your
> comment, I can't figure it out.

it sounds to me like one part of the descriptor claims 192 while another
claims 196, then there is a mismatch and Windows is ignoring the
interface. A quick dump of the descriptors would prove this.
Pavel Hofman July 13, 2021, 1:28 p.m. UTC | #3
Dne 13. 07. 21 v 15:16 Pavel Hofman napsal(a):
> 
> 
> Dne 13. 07. 21 v 14:05 Jerome Brunet napsal(a):
>>
>> On Tue 13 Jul 2021 at 12:22, Pavel Hofman <pavel.hofman@ivitera.com> 
>> wrote:
>>
>>> Hi,
>>>
>>> I am testing the three Ruslan's async feedback patches as modified by
>>> Jerome and I hit a regression in windows 10 enumeration.
>>>
>>> Ruslan posted an already accepted patch
>>> https://github.com/torvalds/linux/commit/789ea77310f0200c84002884ffd628e2baf3ad8a#diff-876615ece7fb56ce8d45fc70623bef9caa2548e810426f217fb785ffa10b33d5 
>>>
>>> which allowed win10 enumeration.
>>>
>>> Ruslan's async feedback patchset kept the change:
>>> https://patchwork.kernel.org/project/linux-usb/patch/1614603943-11668-5-git-send-email-ruslan.bilovol@gmail.com/ 
>>>
>>>
>>> diff --git a/drivers/usb/gadget/function/f_uac2.c
>>> b/drivers/usb/gadget/function/f_uac2.c
>>> index 72b42f8..91b22fb 100644
>>> --- a/drivers/usb/gadget/function/f_uac2.c
>>> +++ b/drivers/usb/gadget/function/f_uac2.c
>>> @@ -506,6 +506,10 @@  static int set_ep_max_packet_size(const struct
>>> f_uac2_opts *uac2_opts,
>>>
>>>       max_size_bw = num_channels(chmask) * ssize *
>>>           ((srate / (factor / (1 << (ep_desc->bInterval - 1)))) + 1);
>>> +
>>> +    if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))
>>> +        max_size_bw = max_size_bw * FBACK_FREQ_MAX / 100;
>>> +
>>>       ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,
>>>                               max_size_ep));
>>>
>>>
>>> Jerome's rebase patch which was accepted recently changed the 
>>> functionality
>>> to the original code:
>>> https://patchwork.kernel.org/project/linux-usb/patch/20210603220104.1216001-4-jbrunet@baylibre.com/ 
>>>
>>>
>>> diff --git a/drivers/usb/gadget/function/f_uac2.c
>>> b/drivers/usb/gadget/function/f_uac2.c
>>> index 321e6c05ba93..ae29ff2b2b68 100644
>>> --- a/drivers/usb/gadget/function/f_uac2.c
>>> +++ b/drivers/usb/gadget/function/f_uac2.c
>>> @@ -584,8 +584,11 @@  static int set_ep_max_packet_size(const struct
>>> f_uac2_opts *uac2_opts,
>>>           ssize = uac2_opts->c_ssize;
>>>       }
>>>
>>> +    if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))
>>> +        srate = srate * (1000 + uac2_opts->fb_max) / 1000;
>>> +
>>>       max_size_bw = num_channels(chmask) * ssize *
>>> -        ((srate / (factor / (1 << (ep_desc->bInterval - 1)))) + 1);
>>> +        DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1)));
>>>       ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,
>>>                               max_size_ep));
>>>
>>> With this version my Win10 does not enumerate the USB AUDIO device, 
>>> even if
>>> it has only EP-IN capability (i.e. is_playback = true). For my setup the
>>> EP-IN wMaxPacketSize is 192bytes vs. 196bytes in Ruslan's version, 
>>> causing
>>> win10 reporting "The specified range could not be found in the range 
>>> list."
>>>
>>
>> Maybe I am lacking USB expertize, but is there any reason why a 192bytes
>> maximum packet size should be considered invalid ? Just from your
>> comment, I can't figure it out.
>>
>> It would help if you could detail the parameters you started your gadget
>> with (rate, format, channel number)
>>
>> IIRC, Ruslan initial patchset reserved a fixed additional bandwidth
>> (around 20% I think) to deal with the explicit feedback.
>>
>> The idea is that, 99.9% of the time, all you need is the ability to fit
>> one more sample in each packet. This is should be what the default
>> setting provides (up to 192kHz). If it does not do that, I made mistake.
>>
>> The setting configurable because I was trying to avoid wasting USB
>> bandwith but still support poor quality platforms where 1 extra sample
>> is not enough (I think Ruslan mentioned having seen such system)
> 
> I am absolutely no USB expert. What I did was testing Jerome's patchset 
> and win10 refused to enumerate, even with the most trivial configuration 
> c_srate=p_srate=48000, 16bits, capture 2ch, playback 0ch which 
> configures no EP-OUT and  no feedback EP-IN. To find the cause I went 
> back one patch (HEAD^) and win10 happily enumerated this no-EP-OUT 
> configuration. So I compared the usb config dump - see attached files 
> from Theosycon USB Descriptor Dumper - see the two attached files, named 
> after commit IDs.
> 
> The dumps differ in only one parameter EP-IN 1 wMaxPacketSize, for both 
> HS and the dumped "Other Speed Configuration Descriptor" i.e. FS:
> 
> diff 650f7f40dc1691a8ab4d1dc411f8f327b36e8d14.txt 
> cb1c270600b2c6f55f55f227775aaddf2cc78bed.txt
> 185c185
> < 0x00C4    wMaxPacketSize    (1 x 196 bytes)
> ---
>  > 0x00C0    wMaxPacketSize    (1 x 192 bytes)
> 339c339
> < 0x00C4    wMaxPacketSize    (1 x 196 bytes)
> ---
>  > 0x00C0    wMaxPacketSize    (1 x 192 bytes)
> 
> So I looked at the patch and saw the changed wMaxPacketSize calculation. 
> Adding +1 yielded what the original Ruslan's code yielded - one more 
> sample (i.e. 196 bytes instead of 192bytes). Therefore I put it in the 
> patch here. This value is accepted by win10.
> 
> I do not know how windows uac2 driver verifies validity of 
> wMaxPacketSize but clearly 196bytes (+1 sample) is accepted while 
> 192bytes is refused. Linux does not care, just like Ruslan described in 
> his commit 789ea77310f020.
> 
> I checked duplex with EP-OUT enabled (i.e. with the feedback EP-IN), the 
> "new" calculation works OK in win10 (while the Jerome's values were 
> refused).
> 
> I really do not know the correct code for calculating the wMaxPacketSize 
> to satisfy the windows driver, but what I am posting works. I'll be 
> happy if someone knowledgeable fixes my layman quickfix.
> 

The original Ruslan's patch (in the mainline branch 
https://github.com/torvalds/linux/commit/789ea77310f0200c84002884ffd628e2baf3ad8a 
) explains the reasoning.
Jerome Brunet July 15, 2021, 9:39 a.m. UTC | #4
On Tue 13 Jul 2021 at 15:16, Pavel Hofman <pavel.hofman@ivitera.com> wrote:

> Dne 13. 07. 21 v 14:05 Jerome Brunet napsal(a):

>> 

>> On Tue 13 Jul 2021 at 12:22, Pavel Hofman <pavel.hofman@ivitera.com> wrote:

>> 

>>> Hi,

>>>

>>> I am testing the three Ruslan's async feedback patches as modified by

>>> Jerome and I hit a regression in windows 10 enumeration.

>>>

>>> Ruslan posted an already accepted patch

>>> https://github.com/torvalds/linux/commit/789ea77310f0200c84002884ffd628e2baf3ad8a#diff-876615ece7fb56ce8d45fc70623bef9caa2548e810426f217fb785ffa10b33d5

>>> which allowed win10 enumeration.

>>>

>>> Ruslan's async feedback patchset kept the change:

>>> https://patchwork.kernel.org/project/linux-usb/patch/1614603943-11668-5-git-send-email-ruslan.bilovol@gmail.com/

>>>

>>> diff --git a/drivers/usb/gadget/function/f_uac2.c

>>> b/drivers/usb/gadget/function/f_uac2.c

>>> index 72b42f8..91b22fb 100644

>>> --- a/drivers/usb/gadget/function/f_uac2.c

>>> +++ b/drivers/usb/gadget/function/f_uac2.c

>>> @@ -506,6 +506,10 @@  static int set_ep_max_packet_size(const struct

>>> f_uac2_opts *uac2_opts,

>>>

>>>   	max_size_bw = num_channels(chmask) * ssize *

>>>   		((srate / (factor / (1 << (ep_desc->bInterval - 1)))) + 1);

>>> +

>>> +	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))

>>> +		max_size_bw = max_size_bw * FBACK_FREQ_MAX / 100;

>>> +

>>>   	ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,

>>>   						    max_size_ep));

>>>

>>>

>>> Jerome's rebase patch which was accepted recently changed the functionality

>>> to the original code:

>>> https://patchwork.kernel.org/project/linux-usb/patch/20210603220104.1216001-4-jbrunet@baylibre.com/

>>>

>>> diff --git a/drivers/usb/gadget/function/f_uac2.c

>>> b/drivers/usb/gadget/function/f_uac2.c

>>> index 321e6c05ba93..ae29ff2b2b68 100644

>>> --- a/drivers/usb/gadget/function/f_uac2.c

>>> +++ b/drivers/usb/gadget/function/f_uac2.c

>>> @@ -584,8 +584,11 @@  static int set_ep_max_packet_size(const struct

>>> f_uac2_opts *uac2_opts,

>>>   		ssize = uac2_opts->c_ssize;

>>>   	}

>>>

>>> +	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))

>>> +		srate = srate * (1000 + uac2_opts->fb_max) / 1000;

>>> +

>>>   	max_size_bw = num_channels(chmask) * ssize *

>>> -		((srate / (factor / (1 << (ep_desc->bInterval - 1)))) + 1);

>>> +		DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1)));

>>>   	ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,

>>>   						    max_size_ep));

>>>

>>> With this version my Win10 does not enumerate the USB AUDIO device, even if

>>> it has only EP-IN capability (i.e. is_playback = true). For my setup the

>>> EP-IN wMaxPacketSize is 192bytes vs. 196bytes in Ruslan's version, causing

>>> win10 reporting "The specified range could not be found in the range list."

>>>

>> 

>> Maybe I am lacking USB expertize, but is there any reason why a 192bytes

>> maximum packet size should be considered invalid ? Just from your

>> comment, I can't figure it out.

>> 

>> It would help if you could detail the parameters you started your gadget

>> with (rate, format, channel number)

>> 

>> IIRC, Ruslan initial patchset reserved a fixed additional bandwidth

>> (around 20% I think) to deal with the explicit feedback.

>> 

>> The idea is that, 99.9% of the time, all you need is the ability to fit

>> one more sample in each packet. This is should be what the default

>> setting provides (up to 192kHz). If it does not do that, I made mistake.

>> 

>> The setting configurable because I was trying to avoid wasting USB

>> bandwith but still support poor quality platforms where 1 extra sample

>> is not enough (I think Ruslan mentioned having seen such system)

>

> I am absolutely no USB expert. What I did was testing Jerome's patchset 

> and win10 refused to enumerate, even with the most trivial configuration 

> c_srate=p_srate=48000, 16bits, capture 2ch, playback 0ch which 

> configures no EP-OUT and  no feedback EP-IN. To find the cause I went 

> back one patch (HEAD^) and win10 happily enumerated this no-EP-OUT 

> configuration. So I compared the usb config dump - see attached files 

> from Theosycon USB Descriptor Dumper - see the two attached files, named 

> after commit IDs.


So 48kHz / 2ch / 16bits. Let's assume USB_SPEED_FULL for example (result
is the same for the other speeds).

In such condition, the nominal packet size is 192B but to accomodate an
extra sample, the maximum should indeed be 196B.

	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))
		srate = srate * (1000 + uac2_opts->fb_max) / 1000;

with fb_max being 5 by default, srate should be 48240 after this.


	max_size_bw = num_channels(chmask) * ssize *
		DIV_ROUND_UP(srate, factor / (1 << (bInterval - 1)));

With USB_SPEED_FULL, bInterval is 1 and factor is 1000 so:
=> DIV_ROUND_UP(48240, 1000 / 1) should give 49;

Then
=> max_size_bw = 2 * 2 * 49 = 196

So the end result should be 196 with current code. I tried on an ARM64
platform. Here is what I get:

[   26.241946] set_ep_max_packet_size: speed is USB_SPEED_FULL 
[   26.243208] set_ep_max_packet_size: intermediate Playback srate 48000
[   26.249758] set_ep_max_packet_size: max_size_bw 192
[   26.254559] set_ep_max_packet_size: speed is USB_SPEED_FULL 
[   26.260130] set_ep_max_packet_size: intermediate Capture srate 48240
[   26.266401] set_ep_max_packet_size: max_size_bw 196
[   26.271209] set_ep_max_packet_size: speed is USB_SPEED_HIGH 
[   26.276873] set_ep_max_packet_size: intermediate Playback srate 48000
[   26.283165] set_ep_max_packet_size: max_size_bw 192
[   26.288015] set_ep_max_packet_size: speed is USB_SPEED_HIGH 
[   26.293691] set_ep_max_packet_size: intermediate Capture srate 48240
[   26.299965] set_ep_max_packet_size: max_size_bw 196
[   26.304753] set_ep_max_packet_size: speed is USB_SPEED_SUPER 
[   26.310426] set_ep_max_packet_size: intermediate Playback srate 48000
[   26.316805] set_ep_max_packet_size: max_size_bw 192
[   26.321625] set_ep_max_packet_size: speed is USB_SPEED_SUPER 
[   26.327309] set_ep_max_packet_size: intermediate Capture srate 48240
[   26.333613] set_ep_max_packet_size: max_size_bw 196

All seems OK and as expected with what's in mainline ATM.
So I'm not quite sure why you would get a different result. It would be
great if you could check further.

>

> The dumps differ in only one parameter EP-IN 1 wMaxPacketSize, for both 

> HS and the dumped "Other Speed Configuration Descriptor" i.e. FS:

>

> diff 650f7f40dc1691a8ab4d1dc411f8f327b36e8d14.txt 

> cb1c270600b2c6f55f55f227775aaddf2cc78bed.txt

> 185c185

> < 0x00C4	wMaxPacketSize    (1 x 196 bytes)

> ---

>  > 0x00C0	wMaxPacketSize    (1 x 192 bytes)

> 339c339

> < 0x00C4	wMaxPacketSize    (1 x 196 bytes)

> ---

>  > 0x00C0	wMaxPacketSize    (1 x 192 bytes)

>

> So I looked at the patch and saw the changed wMaxPacketSize calculation. 

> Adding +1 yielded what the original Ruslan's code yielded - one more 

> sample (i.e. 196 bytes instead of 192bytes). Therefore I put it in the 

> patch here. This value is accepted by win10.

>

> I do not know how windows uac2 driver verifies validity of 

> wMaxPacketSize but clearly 196bytes (+1 sample) is accepted while 

> 192bytes is refused. Linux does not care, just like Ruslan described in 

> his commit 789ea77310f020.

>

> I checked duplex with EP-OUT enabled (i.e. with the feedback EP-IN), the 

> "new" calculation works OK in win10 (while the Jerome's values were 

> refused).

>

> I really do not know the correct code for calculating the wMaxPacketSize 

> to satisfy the windows driver, but what I am posting works. I'll be 

> happy if someone knowledgeable fixes my layman quickfix.

>

> Best regards,

>

> Pavel.
Pavel Hofman July 15, 2021, 12:36 p.m. UTC | #5
Dne 15. 07. 21 v 11:39 Jerome Brunet napsal(a):
> 

> On Tue 13 Jul 2021 at 15:16, Pavel Hofman <pavel.hofman@ivitera.com> wrote:

> 

>> Dne 13. 07. 21 v 14:05 Jerome Brunet napsal(a):

>>>

>>> On Tue 13 Jul 2021 at 12:22, Pavel Hofman <pavel.hofman@ivitera.com> wrote:

>>>

>>>> Hi,

>>>>

>>>> I am testing the three Ruslan's async feedback patches as modified by

>>>> Jerome and I hit a regression in windows 10 enumeration.

>>>>

>>>> Ruslan posted an already accepted patch

>>>> https://github.com/torvalds/linux/commit/789ea77310f0200c84002884ffd628e2baf3ad8a#diff-876615ece7fb56ce8d45fc70623bef9caa2548e810426f217fb785ffa10b33d5

>>>> which allowed win10 enumeration.

>>>>

>>>> Ruslan's async feedback patchset kept the change:

>>>> https://patchwork.kernel.org/project/linux-usb/patch/1614603943-11668-5-git-send-email-ruslan.bilovol@gmail.com/

>>>>

>>>> diff --git a/drivers/usb/gadget/function/f_uac2.c

>>>> b/drivers/usb/gadget/function/f_uac2.c

>>>> index 72b42f8..91b22fb 100644

>>>> --- a/drivers/usb/gadget/function/f_uac2.c

>>>> +++ b/drivers/usb/gadget/function/f_uac2.c

>>>> @@ -506,6 +506,10 @@  static int set_ep_max_packet_size(const struct

>>>> f_uac2_opts *uac2_opts,

>>>>

>>>>    	max_size_bw = num_channels(chmask) * ssize *

>>>>    		((srate / (factor / (1 << (ep_desc->bInterval - 1)))) + 1);

>>>> +

>>>> +	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))

>>>> +		max_size_bw = max_size_bw * FBACK_FREQ_MAX / 100;

>>>> +

>>>>    	ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,

>>>>    						    max_size_ep));

>>>>

>>>>

>>>> Jerome's rebase patch which was accepted recently changed the functionality

>>>> to the original code:

>>>> https://patchwork.kernel.org/project/linux-usb/patch/20210603220104.1216001-4-jbrunet@baylibre.com/

>>>>

>>>> diff --git a/drivers/usb/gadget/function/f_uac2.c

>>>> b/drivers/usb/gadget/function/f_uac2.c

>>>> index 321e6c05ba93..ae29ff2b2b68 100644

>>>> --- a/drivers/usb/gadget/function/f_uac2.c

>>>> +++ b/drivers/usb/gadget/function/f_uac2.c

>>>> @@ -584,8 +584,11 @@  static int set_ep_max_packet_size(const struct

>>>> f_uac2_opts *uac2_opts,

>>>>    		ssize = uac2_opts->c_ssize;

>>>>    	}

>>>>

>>>> +	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))

>>>> +		srate = srate * (1000 + uac2_opts->fb_max) / 1000;

>>>> +

>>>>    	max_size_bw = num_channels(chmask) * ssize *

>>>> -		((srate / (factor / (1 << (ep_desc->bInterval - 1)))) + 1);

>>>> +		DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1)));

>>>>    	ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,

>>>>    						    max_size_ep));

>>>>

>>>> With this version my Win10 does not enumerate the USB AUDIO device, even if

>>>> it has only EP-IN capability (i.e. is_playback = true). For my setup the

>>>> EP-IN wMaxPacketSize is 192bytes vs. 196bytes in Ruslan's version, causing

>>>> win10 reporting "The specified range could not be found in the range list."

>>>>

>>>

>>> Maybe I am lacking USB expertize, but is there any reason why a 192bytes

>>> maximum packet size should be considered invalid ? Just from your

>>> comment, I can't figure it out.

>>>

>>> It would help if you could detail the parameters you started your gadget

>>> with (rate, format, channel number)

>>>

>>> IIRC, Ruslan initial patchset reserved a fixed additional bandwidth

>>> (around 20% I think) to deal with the explicit feedback.

>>>

>>> The idea is that, 99.9% of the time, all you need is the ability to fit

>>> one more sample in each packet. This is should be what the default

>>> setting provides (up to 192kHz). If it does not do that, I made mistake.

>>>

>>> The setting configurable because I was trying to avoid wasting USB

>>> bandwith but still support poor quality platforms where 1 extra sample

>>> is not enough (I think Ruslan mentioned having seen such system)

>>

>> I am absolutely no USB expert. What I did was testing Jerome's patchset

>> and win10 refused to enumerate, even with the most trivial configuration

>> c_srate=p_srate=48000, 16bits, capture 2ch, playback 0ch which

>> configures no EP-OUT and  no feedback EP-IN. To find the cause I went

>> back one patch (HEAD^) and win10 happily enumerated this no-EP-OUT

>> configuration. So I compared the usb config dump - see attached files

>> from Theosycon USB Descriptor Dumper - see the two attached files, named

>> after commit IDs.

> 

> So 48kHz / 2ch / 16bits. Let's assume USB_SPEED_FULL for example (result

> is the same for the other speeds).

> 

> In such condition, the nominal packet size is 192B but to accomodate an

> extra sample, the maximum should indeed be 196B.

> 

> 	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))

> 		srate = srate * (1000 + uac2_opts->fb_max) / 1000;

> 

> with fb_max being 5 by default, srate should be 48240 after this.

> 

> 

> 	max_size_bw = num_channels(chmask) * ssize *

> 		DIV_ROUND_UP(srate, factor / (1 << (bInterval - 1)));

> 

> With USB_SPEED_FULL, bInterval is 1 and factor is 1000 so:

> => DIV_ROUND_UP(48240, 1000 / 1) should give 49;

> 

> Then

> => max_size_bw = 2 * 2 * 49 = 196

> 

> So the end result should be 196 with current code. I tried on an ARM64

> platform. Here is what I get:

> 

> [   26.241946] set_ep_max_packet_size: speed is USB_SPEED_FULL

> [   26.243208] set_ep_max_packet_size: intermediate Playback srate 48000

> [   26.249758] set_ep_max_packet_size: max_size_bw 192

> [   26.254559] set_ep_max_packet_size: speed is USB_SPEED_FULL

> [   26.260130] set_ep_max_packet_size: intermediate Capture srate 48240

> [   26.266401] set_ep_max_packet_size: max_size_bw 196

> [   26.271209] set_ep_max_packet_size: speed is USB_SPEED_HIGH

> [   26.276873] set_ep_max_packet_size: intermediate Playback srate 48000

> [   26.283165] set_ep_max_packet_size: max_size_bw 192

> [   26.288015] set_ep_max_packet_size: speed is USB_SPEED_HIGH

> [   26.293691] set_ep_max_packet_size: intermediate Capture srate 48240

> [   26.299965] set_ep_max_packet_size: max_size_bw 196

> [   26.304753] set_ep_max_packet_size: speed is USB_SPEED_SUPER

> [   26.310426] set_ep_max_packet_size: intermediate Playback srate 48000

> [   26.316805] set_ep_max_packet_size: max_size_bw 192

> [   26.321625] set_ep_max_packet_size: speed is USB_SPEED_SUPER

> [   26.327309] set_ep_max_packet_size: intermediate Capture srate 48240

> [   26.333613] set_ep_max_packet_size: max_size_bw 196

> 

> All seems OK and as expected with what's in mainline ATM.

> So I'm not quite sure why you would get a different result. It would be

> great if you could check further.

> 


The problem is max_size_bw=192 for the Playback (i.e. is_playback = 
true). If only capture direction is activated (p_chmask=0), only EP-OUT 
with max_size_bw=196 is generated and Win10 enumerates the playback-only 
audio device. Once the other direction with max_size_bw=192 is activated 
(either duplex or capture-only), Win10 refuses to enumerate.

This generates 196bytes for each direction and works OK in Win10:

diff --git a/drivers/usb/gadget/function/f_uac2.c 
b/drivers/usb/gadget/function/f_uac2.c
index ae29ff2b2b68..f6ccc21972bf 100644
--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -584,11 +584,15 @@ static int set_ep_max_packet_size(const struct 
f_uac2_opts *uac2_opts,
                 ssize = uac2_opts->c_ssize;
         }

-       if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))
+       if (!is_playback && (uac2_opts->c_sync == 
USB_ENDPOINT_SYNC_ASYNC)) {
                 srate = srate * (1000 + uac2_opts->fb_max) / 1000;
+    max_size_bw = num_channels(chmask) * ssize *
+      DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1)));
+       } else {
+           max_size_bw = num_channels(chmask) * ssize *
+        (DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1))) 
+ 1);
+       }

-       max_size_bw = num_channels(chmask) * ssize *
-               DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 
1)));
         ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,
                                                     max_size_ep));


Tested for samplerate 250kHz 2bytes each direction yielding 1008bytes 
for EP-OUT and 1004 bytes for EP-IN - Win10 enumerates OK.


Pavel.
Jerome Brunet July 15, 2021, 1:53 p.m. UTC | #6
On Thu 15 Jul 2021 at 14:36, Pavel Hofman <pavel.hofman@ivitera.com> wrote:

> Dne 15. 07. 21 v 11:39 Jerome Brunet napsal(a):

>> On Tue 13 Jul 2021 at 15:16, Pavel Hofman <pavel.hofman@ivitera.com>

>> wrote:

>> 


>> So 48kHz / 2ch / 16bits. Let's assume USB_SPEED_FULL for example (result

>> is the same for the other speeds).

>> In such condition, the nominal packet size is 192B but to accomodate an

>> extra sample, the maximum should indeed be 196B.

>> 	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))

>> 		srate = srate * (1000 + uac2_opts->fb_max) / 1000;

>> with fb_max being 5 by default, srate should be 48240 after this.

>> 

>> 	max_size_bw = num_channels(chmask) * ssize *

>> 		DIV_ROUND_UP(srate, factor / (1 << (bInterval - 1)));

>> With USB_SPEED_FULL, bInterval is 1 and factor is 1000 so:

>> => DIV_ROUND_UP(48240, 1000 / 1) should give 49;

>> Then

>> => max_size_bw = 2 * 2 * 49 = 196

>> So the end result should be 196 with current code. I tried on an ARM64

>> platform. Here is what I get:

>> [   26.241946] set_ep_max_packet_size: speed is USB_SPEED_FULL

>> [   26.243208] set_ep_max_packet_size: intermediate Playback srate 48000

>> [   26.249758] set_ep_max_packet_size: max_size_bw 192

>> [   26.254559] set_ep_max_packet_size: speed is USB_SPEED_FULL

>> [   26.260130] set_ep_max_packet_size: intermediate Capture srate 48240

>> [   26.266401] set_ep_max_packet_size: max_size_bw 196

>> [   26.271209] set_ep_max_packet_size: speed is USB_SPEED_HIGH

>> [   26.276873] set_ep_max_packet_size: intermediate Playback srate 48000

>> [   26.283165] set_ep_max_packet_size: max_size_bw 192

>> [   26.288015] set_ep_max_packet_size: speed is USB_SPEED_HIGH

>> [   26.293691] set_ep_max_packet_size: intermediate Capture srate 48240

>> [   26.299965] set_ep_max_packet_size: max_size_bw 196

>> [   26.304753] set_ep_max_packet_size: speed is USB_SPEED_SUPER

>> [   26.310426] set_ep_max_packet_size: intermediate Playback srate 48000

>> [   26.316805] set_ep_max_packet_size: max_size_bw 192

>> [   26.321625] set_ep_max_packet_size: speed is USB_SPEED_SUPER

>> [   26.327309] set_ep_max_packet_size: intermediate Capture srate 48240

>> [   26.333613] set_ep_max_packet_size: max_size_bw 196

>> All seems OK and as expected with what's in mainline ATM.

>> So I'm not quite sure why you would get a different result. It would be

>> great if you could check further.

>> 

>

> The problem is max_size_bw=192 for the Playback (i.e. is_playback =

> true). If only capture direction is activated (p_chmask=0), only EP-OUT 

> with max_size_bw=196 is generated and Win10 enumerates the playback-only

> audio device.


Ok, that was not clear before.

> Once the other direction with max_size_bw=192 is activated 

> (either duplex or capture-only), Win10 refuses to enumerate.


Looking further at the format specification [0] (and crawling the web to
decipher it), it seems that

* For isochronous links: packet size must match the nominal rate.
* For async and adaptative: it must match the nominal rate +/- 1
  packet. That is whether we intend on varying the packet size or not.
  
This has several implication
* In async mode, the device is running of its own clock. It has no
  reason to vary the playback packet size but it should still reserve
  bandwidth for an extra packet to satisfy the spec. This seems to be
  your problem and what Win10 insist on.

  When I tested, I had linux on both sides and apparently it is not too
  picky about that.

* If we apply the spec strictly, like Win10 seems to insist on,
  calculating the maximum packet size based on explicit feedback limits
  is wrong too. Whatever happens, it should be +/- 1 around nominal.

Funny thing, is your change puts a +2 capture compared to nominal but
Win10 is not picky on that ...

I'll send a fix to clean this up. Thanks reporting the problem.

[0]: https://www.usb.org/sites/default/files/frmts10.pdf
Pavel Hofman July 15, 2021, 2:22 p.m. UTC | #7
Dne 15. 07. 21 v 15:53 Jerome Brunet napsal(a):
> 

> On Thu 15 Jul 2021 at 14:36, Pavel Hofman <pavel.hofman@ivitera.com> wrote:

> 

>> Dne 15. 07. 21 v 11:39 Jerome Brunet napsal(a):

>>> On Tue 13 Jul 2021 at 15:16, Pavel Hofman <pavel.hofman@ivitera.com>

>>> wrote:

>>>

> 

>>> So 48kHz / 2ch / 16bits. Let's assume USB_SPEED_FULL for example (result

>>> is the same for the other speeds).

>>> In such condition, the nominal packet size is 192B but to accomodate an

>>> extra sample, the maximum should indeed be 196B.

>>> 	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))

>>> 		srate = srate * (1000 + uac2_opts->fb_max) / 1000;

>>> with fb_max being 5 by default, srate should be 48240 after this.

>>>

>>> 	max_size_bw = num_channels(chmask) * ssize *

>>> 		DIV_ROUND_UP(srate, factor / (1 << (bInterval - 1)));

>>> With USB_SPEED_FULL, bInterval is 1 and factor is 1000 so:

>>> => DIV_ROUND_UP(48240, 1000 / 1) should give 49;

>>> Then

>>> => max_size_bw = 2 * 2 * 49 = 196

>>> So the end result should be 196 with current code. I tried on an ARM64

>>> platform. Here is what I get:

>>> [   26.241946] set_ep_max_packet_size: speed is USB_SPEED_FULL

>>> [   26.243208] set_ep_max_packet_size: intermediate Playback srate 48000

>>> [   26.249758] set_ep_max_packet_size: max_size_bw 192

>>> [   26.254559] set_ep_max_packet_size: speed is USB_SPEED_FULL

>>> [   26.260130] set_ep_max_packet_size: intermediate Capture srate 48240

>>> [   26.266401] set_ep_max_packet_size: max_size_bw 196

>>> [   26.271209] set_ep_max_packet_size: speed is USB_SPEED_HIGH

>>> [   26.276873] set_ep_max_packet_size: intermediate Playback srate 48000

>>> [   26.283165] set_ep_max_packet_size: max_size_bw 192

>>> [   26.288015] set_ep_max_packet_size: speed is USB_SPEED_HIGH

>>> [   26.293691] set_ep_max_packet_size: intermediate Capture srate 48240

>>> [   26.299965] set_ep_max_packet_size: max_size_bw 196

>>> [   26.304753] set_ep_max_packet_size: speed is USB_SPEED_SUPER

>>> [   26.310426] set_ep_max_packet_size: intermediate Playback srate 48000

>>> [   26.316805] set_ep_max_packet_size: max_size_bw 192

>>> [   26.321625] set_ep_max_packet_size: speed is USB_SPEED_SUPER

>>> [   26.327309] set_ep_max_packet_size: intermediate Capture srate 48240

>>> [   26.333613] set_ep_max_packet_size: max_size_bw 196

>>> All seems OK and as expected with what's in mainline ATM.

>>> So I'm not quite sure why you would get a different result. It would be

>>> great if you could check further.

>>>

>>

>> The problem is max_size_bw=192 for the Playback (i.e. is_playback =

>> true). If only capture direction is activated (p_chmask=0), only EP-OUT

>> with max_size_bw=196 is generated and Win10 enumerates the playback-only

>> audio device.

> 

> Ok, that was not clear before.

> 

>> Once the other direction with max_size_bw=192 is activated

>> (either duplex or capture-only), Win10 refuses to enumerate.

> 

> Looking further at the format specification [0] (and crawling the web to

> decipher it), it seems that

> 

> * For isochronous links: packet size must match the nominal rate.

> * For async and adaptative: it must match the nominal rate +/- 1

>    packet. That is whether we intend on varying the packet size or not.

>    

> This has several implication

> * In async mode, the device is running of its own clock. It has no

>    reason to vary the playback packet size but it should still reserve

>    bandwidth for an extra packet to satisfy the spec. This seems to be

>    your problem and what Win10 insist on.

> 

>    When I tested, I had linux on both sides and apparently it is not too

>    picky about that.


Linux also accepts the async EP-OUT without the explicit feedback EP-IN, 
unlike Win10. It also supports implicit async feedback, unlike Win10.

But the WASAPI usbaudio2.sys driver in Win10 seems quite OK, I just 
tested 1536kHz/2ch/16bits playback and works OK, also non-standard 
samplerates are supported (I tested 512kHz/2ch/32bit), all with overhead 
of the Win10 running in VMWare Player virtualization.

> 

> * If we apply the spec strictly, like Win10 seems to insist on,

>    calculating the maximum packet size based on explicit feedback limits

>    is wrong too. Whatever happens, it should be +/- 1 around nominal.

> 

> Funny thing, is your change puts a +2 capture compared to nominal but

> Win10 is not picky on that ...


IMO the Win10 driver just makes sure the max packet size is at least the 
maximum in the specs. If it's more, it does not care - more USB 
bandwidth is wasted, but the operation is safe.

> 

> I'll send a fix to clean this up. Thanks reporting the problem.


Thanks a lot,

Pavel.
Jassi Brar July 15, 2021, 5:52 p.m. UTC | #8
On Thu, Jul 15, 2021 at 12:40 PM Jerome Brunet <jbrunet@baylibre.com> wrote:
>

>

> On Thu 15 Jul 2021 at 14:36, Pavel Hofman <pavel.hofman@ivitera.com> wrote:

>

> > Dne 15. 07. 21 v 11:39 Jerome Brunet napsal(a):

> >> On Tue 13 Jul 2021 at 15:16, Pavel Hofman <pavel.hofman@ivitera.com>

> >> wrote:

> >>

>

> >> So 48kHz / 2ch / 16bits. Let's assume USB_SPEED_FULL for example (result

> >> is the same for the other speeds).

> >> In such condition, the nominal packet size is 192B but to accomodate an

> >> extra sample, the maximum should indeed be 196B.

> >>      if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))

> >>              srate = srate * (1000 + uac2_opts->fb_max) / 1000;

> >> with fb_max being 5 by default, srate should be 48240 after this.

> >>

> >>      max_size_bw = num_channels(chmask) * ssize *

> >>              DIV_ROUND_UP(srate, factor / (1 << (bInterval - 1)));

> >> With USB_SPEED_FULL, bInterval is 1 and factor is 1000 so:

> >> => DIV_ROUND_UP(48240, 1000 / 1) should give 49;

> >> Then

> >> => max_size_bw = 2 * 2 * 49 = 196

> >> So the end result should be 196 with current code. I tried on an ARM64

> >> platform. Here is what I get:

> >> [   26.241946] set_ep_max_packet_size: speed is USB_SPEED_FULL

> >> [   26.243208] set_ep_max_packet_size: intermediate Playback srate 48000

> >> [   26.249758] set_ep_max_packet_size: max_size_bw 192

> >> [   26.254559] set_ep_max_packet_size: speed is USB_SPEED_FULL

> >> [   26.260130] set_ep_max_packet_size: intermediate Capture srate 48240

> >> [   26.266401] set_ep_max_packet_size: max_size_bw 196

> >> [   26.271209] set_ep_max_packet_size: speed is USB_SPEED_HIGH

> >> [   26.276873] set_ep_max_packet_size: intermediate Playback srate 48000

> >> [   26.283165] set_ep_max_packet_size: max_size_bw 192

> >> [   26.288015] set_ep_max_packet_size: speed is USB_SPEED_HIGH

> >> [   26.293691] set_ep_max_packet_size: intermediate Capture srate 48240

> >> [   26.299965] set_ep_max_packet_size: max_size_bw 196

> >> [   26.304753] set_ep_max_packet_size: speed is USB_SPEED_SUPER

> >> [   26.310426] set_ep_max_packet_size: intermediate Playback srate 48000

> >> [   26.316805] set_ep_max_packet_size: max_size_bw 192

> >> [   26.321625] set_ep_max_packet_size: speed is USB_SPEED_SUPER

> >> [   26.327309] set_ep_max_packet_size: intermediate Capture srate 48240

> >> [   26.333613] set_ep_max_packet_size: max_size_bw 196

> >> All seems OK and as expected with what's in mainline ATM.

> >> So I'm not quite sure why you would get a different result. It would be

> >> great if you could check further.

> >>

> >

> > The problem is max_size_bw=192 for the Playback (i.e. is_playback =

> > true). If only capture direction is activated (p_chmask=0), only EP-OUT

> > with max_size_bw=196 is generated and Win10 enumerates the playback-only

> > audio device.

>

> Ok, that was not clear before.

>

> > Once the other direction with max_size_bw=192 is activated

> > (either duplex or capture-only), Win10 refuses to enumerate.

>

> Looking further at the format specification [0] (and crawling the web to

> decipher it), it seems that

>

> * For isochronous links: packet size must match the nominal rate.

> * For async and adaptative: it must match the nominal rate +/- 1

>   packet. That is whether we intend on varying the packet size or not.

>

> This has several implication

> * In async mode, the device is running of its own clock. It has no

>   reason to vary the playback packet size but it should still reserve

>   bandwidth for an extra packet to satisfy the spec. This seems to be

>   your problem and what Win10 insist on.

>

>   When I tested, I had linux on both sides and apparently it is not too

>   picky about that.

>

> * If we apply the spec strictly, like Win10 seems to insist on,

>   calculating the maximum packet size based on explicit feedback limits

>   is wrong too. Whatever happens, it should be +/- 1 around nominal.

>

IIRC, a couple of years ago, Alan proposed a smart scheme to keep the
UAC2 byterate in exact sync with what's expected over time. You may
have to dig into the alsa archives though.

cheers.
diff mbox series

Patch

diff --git a/drivers/usb/gadget/function/f_uac2.c 
b/drivers/usb/gadget/function/f_uac2.c
index 72b42f8..91b22fb 100644
--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -506,6 +506,10 @@   static int set_ep_max_packet_size(const struct 
f_uac2_opts *uac2_opts,

  	max_size_bw = num_channels(chmask) * ssize *
  		((srate / (factor / (1 << (ep_desc->bInterval - 1)))) + 1);
+
+	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))
+		max_size_bw = max_size_bw * FBACK_FREQ_MAX / 100;
+
  	ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,
  						    max_size_ep));


Jerome's rebase patch which was accepted recently changed the 
functionality to the original code:
https://patchwork.kernel.org/project/linux-usb/patch/20210603220104.1216001-4-jbrunet@baylibre.com/

diff --git a/drivers/usb/gadget/function/f_uac2.c 
b/drivers/usb/gadget/function/f_uac2.c
index 321e6c05ba93..ae29ff2b2b68 100644
--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -584,8 +584,11 @@   static int set_ep_max_packet_size(const struct 
f_uac2_opts *uac2_opts,
  		ssize = uac2_opts->c_ssize;
  	}

+	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))
+		srate = srate * (1000 + uac2_opts->fb_max) / 1000;
+
  	max_size_bw = num_channels(chmask) * ssize *
-		((srate / (factor / (1 << (ep_desc->bInterval - 1)))) + 1);
+		DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1)));
  	ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,
  						    max_size_ep));

With this version my Win10 does not enumerate the USB AUDIO device, even 
if it has only EP-IN capability (i.e. is_playback = true). For my setup 
the EP-IN wMaxPacketSize is 192bytes vs. 196bytes in Ruslan's version, 
causing win10 reporting "The specified range could not be found in the 
range list."

A simple change makes Win10 enumerate both playback-only as well as 
duplex playback/capture async device:

diff --git a/drivers/usb/gadget/function/f_uac2.c 
b/drivers/usb/gadget/function/f_uac2.c
index ae29ff2b2b68..5ba778814796 100644
--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -588,7 +588,7 @@  static int set_ep_max_packet_size(const struct 
f_uac2_opts *uac2_opts,
                 srate = srate * (1000 + uac2_opts->fb_max) / 1000;

         max_size_bw = num_channels(chmask) * ssize *
-               DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 
1)));
+               (DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval 
- 1))) + 1);
         ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,