mbox series

[RFC,00/13] drm/msm: Add Display Stream Compression Support

Message ID 20210521124946.3617862-1-vkoul@kernel.org
Headers show
Series drm/msm: Add Display Stream Compression Support | expand

Message

Vinod Koul May 21, 2021, 12:49 p.m. UTC
Display Stream Compression (DSC) compresses the display stream in host which
is later decoded by panel. This series enables this for Qualcomm msm driver.
This was tested on Google Pixel3 phone which use LGE SW43408 panel.

The changes include adding DT properties for DSC then hardware blocks support
required in DPU1 driver and support in encoder. We also add support in DSI
and introduce required topology changes.

In order for panel to set the DSC parameters we add dsc in drm_panel and set
it from the msm driver.

Complete changes which enable this for Pixel3 along with panel driver (not
part of this series) and DT changes can be found at:
git.linaro.org/people/vinod.koul/kernel.git pixel/dsc_rfc

Comments welcome!

Vinod Koul (13):
  drm/dsc: Add dsc pps header init function
  dt-bindings: msm/dsi: Document Display Stream Compression (DSC)
    parameters
  drm/msm/dsi: add support for dsc data
  drm/msm/disp/dpu1: Add support for DSC
  drm/msm/disp/dpu1: Add support for DSC in pingpong block
  drm/msm/disp/dpu1: Add DSC support in RM
  drm/msm/disp/dpu1: Add DSC for SDM845 to hw_catalog
  drm/msm/disp/dpu1: Add DSC support in hw_ctl
  drm/msm/disp/dpu1: Don't use DSC with mode_3d
  drm/msm/disp/dpu1: Add support for DSC in encoder
  drm/msm/disp/dpu1: Add support for DSC in topology
  drm/msm/dsi: Add support for DSC configuration
  drm/msm/dsi: Pass DSC params to drm_panel

 .../devicetree/bindings/display/msm/dsi.txt   |  15 +
 drivers/gpu/drm/drm_dsc.c                     |  11 +
 drivers/gpu/drm/msm/Makefile                  |   1 +
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c   | 204 +++++++++++-
 .../gpu/drm/msm/disp/dpu1/dpu_encoder_phys.h  |  11 +
 .../drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c  |   2 +
 .../gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c    |  22 ++
 .../gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h    |  26 ++
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_ctl.c    |  12 +-
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_ctl.h    |   2 +
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.c    | 221 +++++++++++++
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.h    |  79 +++++
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_mdss.h   |  13 +
 .../gpu/drm/msm/disp/dpu1/dpu_hw_pingpong.c   |  32 ++
 .../gpu/drm/msm/disp/dpu1/dpu_hw_pingpong.h   |  14 +
 drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h       |   1 +
 drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c        |  32 ++
 drivers/gpu/drm/msm/disp/dpu1/dpu_rm.h        |   1 +
 drivers/gpu/drm/msm/dsi/dsi.xml.h             |  10 +
 drivers/gpu/drm/msm/dsi/dsi_host.c            | 293 +++++++++++++++++-
 drivers/gpu/drm/msm/msm_drv.h                 |  32 ++
 include/drm/drm_dsc.h                         |  16 +
 include/drm/drm_panel.h                       |   7 +
 23 files changed, 1043 insertions(+), 14 deletions(-)
 create mode 100644 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.c
 create mode 100644 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.h

Comments

Vinod Koul May 26, 2021, 5:46 a.m. UTC | #1
Hello Jeff,

On 21-05-21, 08:09, Jeffrey Hugo wrote:
> On Fri, May 21, 2021 at 6:50 AM Vinod Koul <vkoul@kernel.org> wrote:

> >

> > Display Stream Compression (DSC) compresses the display stream in host which

> > is later decoded by panel. This series enables this for Qualcomm msm driver.

> > This was tested on Google Pixel3 phone which use LGE SW43408 panel.

> >

> > The changes include adding DT properties for DSC then hardware blocks support

> > required in DPU1 driver and support in encoder. We also add support in DSI

> > and introduce required topology changes.

> >

> > In order for panel to set the DSC parameters we add dsc in drm_panel and set

> > it from the msm driver.

> >

> > Complete changes which enable this for Pixel3 along with panel driver (not

> > part of this series) and DT changes can be found at:

> > git.linaro.org/people/vinod.koul/kernel.git pixel/dsc_rfc

> >

> > Comments welcome!

> 

> This feels backwards to me.  I've only skimmed this series, and the DT

> changes didn't come through for me, so perhaps I have an incomplete

> view.


Not sure why, I see it on lore:
https://lore.kernel.org/dri-devel/20210521124946.3617862-3-vkoul@kernel.org/

> DSC is not MSM specific.  There is a standard for it.  Yet it looks

> like everything is implemented in a MSM specific way, and then pushed

> to the panel.  So, every vendor needs to implement their vendor

> specific way to get the DSC info, and then push it to the panel?

> Seems wrong, given there is an actual standard for this feature.


I have added slice and bpp info in the DT here under the host and then
pass the generic struct drm_dsc_config to panel which allows panel to
write the pps cmd

Nothing above is MSM specific.. It can very well work with non MSM
controllers too.

I didn't envision DSC to be a specific thing, most of
the patches here are hardware enabling ones for DSC bits for MSM
hardware.

> Additionally, we define panel properties (resolution, BPP, etc) at the

> panel, and have the display drivers pull it from the panel.  However,

> for DSC, you do the reverse (define it in the display driver, and push

> it to the panel).  If the argument is that DSC properties can be

> dynamic, well, so can resolution.  Every panel for MSM MTPs supports

> multiple resolutions, yet we define that with the panel in Linux.


I dont have an answer for that right now, to start with yes the
properties are in host but I am okay to discuss this and put wherever we
feel is most correct thing.  I somehow dont like that we should pull
from panel DT and program host with that. Here using struct
drm_dsc_config allows me to configure panel based on resolution passed

> Finally, I haven't seen the DT bits, but I'm concerned about using DT

> for this.  It inherently excludes ACPI systems.  You appear to have

> sdm845 support in this series, but what about ACPI boot on the Lenovo

> C630 for example?  Or any of the 8cx laptops?  We don't read the panel

> resolution, etc from DT, so why the DSC?


But you must read from somewhere like ACPI tables. I think ACPI systems
would have some ACPI table info out there which would help on this.
Yes that is another task which we need to start with once we enable OF
systems.

Thanks
-- 
~Vinod
Jeffrey Hugo May 26, 2021, 3 p.m. UTC | #2
On Tue, May 25, 2021 at 11:46 PM Vinod Koul <vkoul@kernel.org> wrote:
>
> Hello Jeff,
>
> On 21-05-21, 08:09, Jeffrey Hugo wrote:
> > On Fri, May 21, 2021 at 6:50 AM Vinod Koul <vkoul@kernel.org> wrote:
> > >
> > > Display Stream Compression (DSC) compresses the display stream in host which
> > > is later decoded by panel. This series enables this for Qualcomm msm driver.
> > > This was tested on Google Pixel3 phone which use LGE SW43408 panel.
> > >
> > > The changes include adding DT properties for DSC then hardware blocks support
> > > required in DPU1 driver and support in encoder. We also add support in DSI
> > > and introduce required topology changes.
> > >
> > > In order for panel to set the DSC parameters we add dsc in drm_panel and set
> > > it from the msm driver.
> > >
> > > Complete changes which enable this for Pixel3 along with panel driver (not
> > > part of this series) and DT changes can be found at:
> > > git.linaro.org/people/vinod.koul/kernel.git pixel/dsc_rfc
> > >
> > > Comments welcome!
> >
> > This feels backwards to me.  I've only skimmed this series, and the DT
> > changes didn't come through for me, so perhaps I have an incomplete
> > view.
>
> Not sure why, I see it on lore:
> https://lore.kernel.org/dri-devel/20210521124946.3617862-3-vkoul@kernel.org/
>
> > DSC is not MSM specific.  There is a standard for it.  Yet it looks
> > like everything is implemented in a MSM specific way, and then pushed
> > to the panel.  So, every vendor needs to implement their vendor
> > specific way to get the DSC info, and then push it to the panel?
> > Seems wrong, given there is an actual standard for this feature.
>
> I have added slice and bpp info in the DT here under the host and then
> pass the generic struct drm_dsc_config to panel which allows panel to
> write the pps cmd
>
> Nothing above is MSM specific.. It can very well work with non MSM
> controllers too.

I disagree.

The DT bindings you defined (thanks for the direct link) are MSM
specific.  I'm not talking (yet) about the properties you defined, but
purely from the stand point that you defined the binding within the
scope of the MSM dsi binding.  No other vendor can use those bindings.
Of course, if we look at the properties themselves, they are prefixed
with "qcom", which is vendor specific.

So, purely on the face of it, this is MSM specific.

Assuming we want a DT solution for DSC, I think it should be something
like Documentation/devicetree/bindings/clock/clock-bindings.txt (the
first example that comes to mind), which is a non-vendor specific
generic set of properties that each vendor/device specific binding can
inherit.  Panel has similar things.

Specific to the properties, I don't much like that you duplicate BPP,
which is already associated with the panel (although perhaps not in
the scope of DT).  What if the panel and your DSC bindings disagree?
Also, I guess I need to ask, have you read the DSC spec?  Last I
looked, there were something like 3 dozen properties that could be
configured.  You have five in your proposed binding.  To me, this is
not a generic DSC solution, this is MSM specific (and frankly I don't
think this supports all the configuration the MSM hardware can do,
either).

I'm surprised Rob Herring didn't have more to say on this.

> I didn't envision DSC to be a specific thing, most of
> the patches here are hardware enabling ones for DSC bits for MSM
> hardware.
>
> > Additionally, we define panel properties (resolution, BPP, etc) at the
> > panel, and have the display drivers pull it from the panel.  However,
> > for DSC, you do the reverse (define it in the display driver, and push
> > it to the panel).  If the argument is that DSC properties can be
> > dynamic, well, so can resolution.  Every panel for MSM MTPs supports
> > multiple resolutions, yet we define that with the panel in Linux.
>
> I dont have an answer for that right now, to start with yes the
> properties are in host but I am okay to discuss this and put wherever we
> feel is most correct thing.  I somehow dont like that we should pull
> from panel DT and program host with that. Here using struct
> drm_dsc_config allows me to configure panel based on resolution passed

I somewhat agree that pulling from the panel and programing the host
based on that is an odd solution, but we have it currently.  Have a
look at Documentation/devicetree/bindings/display/panel in particular
panel-timing.  All of that ends up informing the mdss programing
anyways (particularly the dsi and its phy).  So my problem is that we
currently have a solution that seems to just need to be extended, and
instead you have proposed a completely different solution which is
arguably contradictory.

However, I'd like to see thoughts from Rob Clark, David, and any
others that typically handle this stuff (maybe Sam Ravenborg from the
panel side?).  I consider them to be the experts, and if they think
your solution is the way to go, I'll shut up.  I consider myself to be
a novice that has dabbled in this area, and while this currently
doesn't make sense to me, maybe I need some education here to see the
light.

> > Finally, I haven't seen the DT bits, but I'm concerned about using DT
> > for this.  It inherently excludes ACPI systems.  You appear to have
> > sdm845 support in this series, but what about ACPI boot on the Lenovo
> > C630 for example?  Or any of the 8cx laptops?  We don't read the panel
> > resolution, etc from DT, so why the DSC?
>
> But you must read from somewhere like ACPI tables. I think ACPI systems
> would have some ACPI table info out there which would help on this.
> Yes that is another task which we need to start with once we enable OF
> systems.

Frankly, I don't like the MSM ACPI solution that I've seen on the laptops.
The ACPI assumes the entire MDSS (including DSI parts) and GPU is one
device, and ultimately handled by one driver.  That driver needs to
get a value from UEFI (set by the bootloader) that is the "panel id".
Then the driver calls into ACPI (I think its _ROM, but I might be
mistaken, doing this from memory) with that id.  It gets back a binary
blob which is mostly an xml file (format is publicly documented) that
contains the panel timings and such.

Generally we've defined simple-panel entities for these, with the
timings in code (you can see what Bjorn and I have upstreamed), and
just match on the compatible.

In summary, I don't mean to be difficult, I just think this solution
needs more "baking".
Rob Clark May 27, 2021, 11:30 p.m. UTC | #3
On Wed, May 26, 2021 at 8:00 AM Jeffrey Hugo <jeffrey.l.hugo@gmail.com> wrote:
>

> On Tue, May 25, 2021 at 11:46 PM Vinod Koul <vkoul@kernel.org> wrote:

> >

> > Hello Jeff,

> >

> > On 21-05-21, 08:09, Jeffrey Hugo wrote:

> > > On Fri, May 21, 2021 at 6:50 AM Vinod Koul <vkoul@kernel.org> wrote:

> > > >

> > > > Display Stream Compression (DSC) compresses the display stream in host which

> > > > is later decoded by panel. This series enables this for Qualcomm msm driver.

> > > > This was tested on Google Pixel3 phone which use LGE SW43408 panel.

> > > >

> > > > The changes include adding DT properties for DSC then hardware blocks support

> > > > required in DPU1 driver and support in encoder. We also add support in DSI

> > > > and introduce required topology changes.

> > > >

> > > > In order for panel to set the DSC parameters we add dsc in drm_panel and set

> > > > it from the msm driver.

> > > >

> > > > Complete changes which enable this for Pixel3 along with panel driver (not

> > > > part of this series) and DT changes can be found at:

> > > > git.linaro.org/people/vinod.koul/kernel.git pixel/dsc_rfc

> > > >

> > > > Comments welcome!

> > >

> > > This feels backwards to me.  I've only skimmed this series, and the DT

> > > changes didn't come through for me, so perhaps I have an incomplete

> > > view.

> >

> > Not sure why, I see it on lore:

> > https://lore.kernel.org/dri-devel/20210521124946.3617862-3-vkoul@kernel.org/

> >

> > > DSC is not MSM specific.  There is a standard for it.  Yet it looks

> > > like everything is implemented in a MSM specific way, and then pushed

> > > to the panel.  So, every vendor needs to implement their vendor

> > > specific way to get the DSC info, and then push it to the panel?

> > > Seems wrong, given there is an actual standard for this feature.

> >

> > I have added slice and bpp info in the DT here under the host and then

> > pass the generic struct drm_dsc_config to panel which allows panel to

> > write the pps cmd

> >

> > Nothing above is MSM specific.. It can very well work with non MSM

> > controllers too.

>

> I disagree.

>

> The DT bindings you defined (thanks for the direct link) are MSM

> specific.  I'm not talking (yet) about the properties you defined, but

> purely from the stand point that you defined the binding within the

> scope of the MSM dsi binding.  No other vendor can use those bindings.

> Of course, if we look at the properties themselves, they are prefixed

> with "qcom", which is vendor specific.

>

> So, purely on the face of it, this is MSM specific.

>

> Assuming we want a DT solution for DSC, I think it should be something

> like Documentation/devicetree/bindings/clock/clock-bindings.txt (the

> first example that comes to mind), which is a non-vendor specific

> generic set of properties that each vendor/device specific binding can

> inherit.  Panel has similar things.

>

> Specific to the properties, I don't much like that you duplicate BPP,

> which is already associated with the panel (although perhaps not in

> the scope of DT).  What if the panel and your DSC bindings disagree?

> Also, I guess I need to ask, have you read the DSC spec?  Last I

> looked, there were something like 3 dozen properties that could be

> configured.  You have five in your proposed binding.  To me, this is

> not a generic DSC solution, this is MSM specific (and frankly I don't

> think this supports all the configuration the MSM hardware can do,

> either).

>

> I'm surprised Rob Herring didn't have more to say on this.

>

> > I didn't envision DSC to be a specific thing, most of

> > the patches here are hardware enabling ones for DSC bits for MSM

> > hardware.

> >

> > > Additionally, we define panel properties (resolution, BPP, etc) at the

> > > panel, and have the display drivers pull it from the panel.  However,

> > > for DSC, you do the reverse (define it in the display driver, and push

> > > it to the panel).  If the argument is that DSC properties can be

> > > dynamic, well, so can resolution.  Every panel for MSM MTPs supports

> > > multiple resolutions, yet we define that with the panel in Linux.

> >

> > I dont have an answer for that right now, to start with yes the

> > properties are in host but I am okay to discuss this and put wherever we

> > feel is most correct thing.  I somehow dont like that we should pull

> > from panel DT and program host with that. Here using struct

> > drm_dsc_config allows me to configure panel based on resolution passed

>

> I somewhat agree that pulling from the panel and programing the host

> based on that is an odd solution, but we have it currently.  Have a

> look at Documentation/devicetree/bindings/display/panel in particular

> panel-timing.  All of that ends up informing the mdss programing

> anyways (particularly the dsi and its phy).  So my problem is that we

> currently have a solution that seems to just need to be extended, and

> instead you have proposed a completely different solution which is

> arguably contradictory.

>

> However, I'd like to see thoughts from Rob Clark, David, and any

> others that typically handle this stuff (maybe Sam Ravenborg from the

> panel side?).  I consider them to be the experts, and if they think

> your solution is the way to go, I'll shut up.  I consider myself to be

> a novice that has dabbled in this area, and while this currently

> doesn't make sense to me, maybe I need some education here to see the

> light.

>

> > > Finally, I haven't seen the DT bits, but I'm concerned about using DT

> > > for this.  It inherently excludes ACPI systems.  You appear to have

> > > sdm845 support in this series, but what about ACPI boot on the Lenovo

> > > C630 for example?  Or any of the 8cx laptops?  We don't read the panel

> > > resolution, etc from DT, so why the DSC?

> >

> > But you must read from somewhere like ACPI tables. I think ACPI systems

> > would have some ACPI table info out there which would help on this.

> > Yes that is another task which we need to start with once we enable OF

> > systems.

>

> Frankly, I don't like the MSM ACPI solution that I've seen on the laptops.

> The ACPI assumes the entire MDSS (including DSI parts) and GPU is one

> device, and ultimately handled by one driver.  That driver needs to

> get a value from UEFI (set by the bootloader) that is the "panel id".

> Then the driver calls into ACPI (I think its _ROM, but I might be

> mistaken, doing this from memory) with that id.  It gets back a binary

> blob which is mostly an xml file (format is publicly documented) that

> contains the panel timings and such.


tbh, I kinda suspect that having a single "gpu" device (which also
includes venus, in addition to display, IIRC) in the ACPI tables is a
windowsism, trying to make things look to userspace like a single "GPU
card" in the x86 world.. but either way, I think the ACPI tables on
the windows arm laptops which use dsi->bridge->edp is too much of a
lost cause to even consider here.  Possibly ACPI boot on these devices
would be more feasible on newer devices which have direct eDP out of
the SoC without requiring external bridge/panel glue.

I'd worry more about what makes sense in a DT world, when it comes to
DT bindings.

BR,
-R

> Generally we've defined simple-panel entities for these, with the

> timings in code (you can see what Bjorn and I have upstreamed), and

> just match on the compatible.

>

> In summary, I don't mean to be difficult, I just think this solution

> needs more "baking".
Vinod Koul June 2, 2021, 11:01 a.m. UTC | #4
On 27-05-21, 16:30, Rob Clark wrote:
> On Wed, May 26, 2021 at 8:00 AM Jeffrey Hugo <jeffrey.l.hugo@gmail.com> wrote:

> > On Tue, May 25, 2021 at 11:46 PM Vinod Koul <vkoul@kernel.org> wrote:


> > Frankly, I don't like the MSM ACPI solution that I've seen on the laptops.

> > The ACPI assumes the entire MDSS (including DSI parts) and GPU is one

> > device, and ultimately handled by one driver.  That driver needs to

> > get a value from UEFI (set by the bootloader) that is the "panel id".

> > Then the driver calls into ACPI (I think its _ROM, but I might be

> > mistaken, doing this from memory) with that id.  It gets back a binary

> > blob which is mostly an xml file (format is publicly documented) that

> > contains the panel timings and such.

> 

> tbh, I kinda suspect that having a single "gpu" device (which also

> includes venus, in addition to display, IIRC) in the ACPI tables is a

> windowsism, trying to make things look to userspace like a single "GPU

> card" in the x86 world.. but either way, I think the ACPI tables on

> the windows arm laptops which use dsi->bridge->edp is too much of a

> lost cause to even consider here.  Possibly ACPI boot on these devices

> would be more feasible on newer devices which have direct eDP out of

> the SoC without requiring external bridge/panel glue.


yeah that is always a very different world. although it might make sense
to use information in tables and try to deduce information about the
system can be helpful...

> I'd worry more about what makes sense in a DT world, when it comes to

> DT bindings.


And do you have thoughts on that..?

-- 
~Vinod
Abhinav Kumar June 3, 2021, 11:40 p.m. UTC | #5
On 2021-06-02 04:01, Vinod Koul wrote:
> On 27-05-21, 16:30, Rob Clark wrote:
>> On Wed, May 26, 2021 at 8:00 AM Jeffrey Hugo 
>> <jeffrey.l.hugo@gmail.com> wrote:
>> > On Tue, May 25, 2021 at 11:46 PM Vinod Koul <vkoul@kernel.org> wrote:
> 
>> > Frankly, I don't like the MSM ACPI solution that I've seen on the laptops.
>> > The ACPI assumes the entire MDSS (including DSI parts) and GPU is one
>> > device, and ultimately handled by one driver.  That driver needs to
>> > get a value from UEFI (set by the bootloader) that is the "panel id".
>> > Then the driver calls into ACPI (I think its _ROM, but I might be
>> > mistaken, doing this from memory) with that id.  It gets back a binary
>> > blob which is mostly an xml file (format is publicly documented) that
>> > contains the panel timings and such.
>> 
>> tbh, I kinda suspect that having a single "gpu" device (which also
>> includes venus, in addition to display, IIRC) in the ACPI tables is a
>> windowsism, trying to make things look to userspace like a single "GPU
>> card" in the x86 world.. but either way, I think the ACPI tables on
>> the windows arm laptops which use dsi->bridge->edp is too much of a
>> lost cause to even consider here.  Possibly ACPI boot on these devices
>> would be more feasible on newer devices which have direct eDP out of
>> the SoC without requiring external bridge/panel glue.
> 
> yeah that is always a very different world. although it might make 
> sense
> to use information in tables and try to deduce information about the
> system can be helpful...
> 
>> I'd worry more about what makes sense in a DT world, when it comes to
>> DT bindings.
> 
> And do you have thoughts on that..?

At the moment, I will comment on the bindings first and my idea on how 
to proceed.
The bindings mentioned here: 
https://lore.kernel.org/dri-devel/20210521124946.3617862-3-vkoul@kernel.org/ 
seem to be just
taken directly from downstream which was not the plan.

I think all of these should be part of the generic panel bindings as 
none of these are QC specific:

@@ -188,6 +195,14 @@ Example:
  		qcom,master-dsi;
  		qcom,sync-dual-dsi;

+		qcom,mdss-dsc-enabled;
+		qcom,mdss-slice-height = <16>;
+		qcom,mdss-slice-width = <540>;
+		qcom,mdss-slice-per-pkt = <1>;
+		qcom,mdss-bit-per-component = <8>;
+		qcom,mdss-bit-per-pixel = <8>;
+		qcom,mdss-block-prediction-enable;
+

How about having a panel-dsc.yaml which will have these properties and 
have a panel-dsc node to have this information?

I would like to hear the feedback on this proposal then the series can 
be reworked.

Thanks

Abhinav
Rob Clark June 4, 2021, 2:36 a.m. UTC | #6
On Wed, Jun 2, 2021 at 4:01 AM Vinod Koul <vkoul@kernel.org> wrote:
>
> On 27-05-21, 16:30, Rob Clark wrote:
> > On Wed, May 26, 2021 at 8:00 AM Jeffrey Hugo <jeffrey.l.hugo@gmail.com> wrote:
> > > On Tue, May 25, 2021 at 11:46 PM Vinod Koul <vkoul@kernel.org> wrote:
>
> > > Frankly, I don't like the MSM ACPI solution that I've seen on the laptops.
> > > The ACPI assumes the entire MDSS (including DSI parts) and GPU is one
> > > device, and ultimately handled by one driver.  That driver needs to
> > > get a value from UEFI (set by the bootloader) that is the "panel id".
> > > Then the driver calls into ACPI (I think its _ROM, but I might be
> > > mistaken, doing this from memory) with that id.  It gets back a binary
> > > blob which is mostly an xml file (format is publicly documented) that
> > > contains the panel timings and such.
> >
> > tbh, I kinda suspect that having a single "gpu" device (which also
> > includes venus, in addition to display, IIRC) in the ACPI tables is a
> > windowsism, trying to make things look to userspace like a single "GPU
> > card" in the x86 world.. but either way, I think the ACPI tables on
> > the windows arm laptops which use dsi->bridge->edp is too much of a
> > lost cause to even consider here.  Possibly ACPI boot on these devices
> > would be more feasible on newer devices which have direct eDP out of
> > the SoC without requiring external bridge/panel glue.
>
> yeah that is always a very different world. although it might make sense
> to use information in tables and try to deduce information about the
> system can be helpful...
>
> > I'd worry more about what makes sense in a DT world, when it comes to
> > DT bindings.
>
> And do you have thoughts on that..?

Only that I wouldn't get too hung up on existing snapdragon ACPI
tables.. not sure if there is prior art as far as ACPI tables for this
on x86 systems, if so that *might* be a thing to consider, but
otherwise it does sound a bit like we want less qcom specific bindings
here.  But other than that I'll leave it to folks who spend more time
thinking about bindings.. left to my own devices I'd come up with a
point solution and go back to working on mesa, so that probably isn't
the opinion you want to follow ;-)

BR,
-R
Vinod Koul June 17, 2021, 8:06 a.m. UTC | #7
On 03-06-21, 16:40, abhinavk@codeaurora.org wrote:
> On 2021-06-02 04:01, Vinod Koul wrote:
> > On 27-05-21, 16:30, Rob Clark wrote:
> > 
> > yeah that is always a very different world. although it might make sense
> > to use information in tables and try to deduce information about the
> > system can be helpful...
> > 
> > > I'd worry more about what makes sense in a DT world, when it comes to
> > > DT bindings.
> > 
> > And do you have thoughts on that..?
> 
> At the moment, I will comment on the bindings first and my idea on how to
> proceed.
> The bindings mentioned here:
> https://lore.kernel.org/dri-devel/20210521124946.3617862-3-vkoul@kernel.org/
> seem to be just
> taken directly from downstream which was not the plan.
> 
> I think all of these should be part of the generic panel bindings as none of
> these are QC specific:

Okay so we have discussed this w/ Bjorn and Abhinav and here are the
conclusions and recommendations for binding

1. the properties are generic and not msm specific
2. The host supports multiple formats but the one we choose depends
mostly upon panel. Notably host runs the config which the panel supports.

So the recommendations is to add a table of dsc properties in the panel
driver. No DT binding here.

I should also note that for DP we should be able to calculate these
values from EDID like the i915 driver seems to do

With this I will drop the binding patch and move dsc properties to panel
driver

Thanks