diff mbox series

[5/8] dt_bindings: rs485: Correct delay values

Message ID 20220622154659.8710-6-LinoSanfilippo@gmx.de
State Superseded
Headers show
Series None | expand

Commit Message

Lino Sanfilippo June 22, 2022, 3:46 p.m. UTC 
From: Lino Sanfilippo <l.sanfilippo@kunbus.com>

The maximum allowed delay for RTS before and RTS after send is 100 ms.
Adjust the documentation accordingly.

Signed-off-by: Lino Sanfilippo <l.sanfilippo@kunbus.com>
---
 Documentation/devicetree/bindings/serial/rs485.yaml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Lino Sanfilippo June 29, 2022, 11:50 p.m. UTC | #1 
On 28.06.22 12:03, Andy Shevchenko wrote:
> On Thu, Jun 23, 2022 at 10:17:06PM +0200, Lino Sanfilippo wrote:
>> On 23.06.22 at 18:29, Andy Shevchenko wrote:
>>> On Wed, Jun 22, 2022 at 05:46:56PM +0200, Lino Sanfilippo wrote:
>>>>
>>>> The maximum allowed delay for RTS before and RTS after send is 100 ms.
>>>> Adjust the documentation accordingly.
>>>
>>> Is it only documentation issue? If the code allows this to be set higher
>>> than 100, we may not change the documentation since this an ABI (from
>>> firmware <--> kernel perspective) we need to support old variants.
>>
>> Well currently the documentation claims that a maximum of 1000 msecs is allowed but
>> nothing actually checks the values read from device tree/ACPI and so it is possible
>> to set much higher values (note that the UART drivers dont check the delays read from
>> DT/ACPI either, the only exception I found is max310x which clamps it to 15 ms).
>>
>> We already have a maximum of 100 ms defined for RTS delays set via TIOCSRS485. To be
>> consistent with TIOCSRS485 the same limit is used for DT/ACPI values in this patch.
>>
>> I am aware that this changes the firmware/kernel ABI. But we had a similar situation when
>> the sanity checks for TIOCSRS485 were introduced
>> (see https://lore.kernel.org/all/20220410104642.32195-2-LinoSanfilippo@gmx.de/)
>> since before we did not have those limits for all drivers (some drivers clamped the
>> values itself but many did not care).
>> Furthermore 100 ms is already a very high value for RTS delays (which are usually rather
>> in usecs range). So IMHO the risk is very low to break anything when values are clamped
>> that are higher than that.
>
> You need to elaborate all this in the commit message to justify the change.
>

OK, I see. I will rewrite the commit message then to hopefully make the rationale behind
the time reduction more clear.

Thanks,
Lino
diff mbox series

Patch

diff --git a/Documentation/devicetree/bindings/serial/rs485.yaml b/Documentation/devicetree/bindings/serial/rs485.yaml
index f2c9c9fe6aa7..90a1bab40f05 100644
--- a/Documentation/devicetree/bindings/serial/rs485.yaml
+++ b/Documentation/devicetree/bindings/serial/rs485.yaml
@@ -22,12 +22,12 @@  properties:
         - description: Delay between rts signal and beginning of data sent in
             milliseconds. It corresponds to the delay before sending data.
           default: 0
-          maximum: 1000
+          maximum: 100
         - description: Delay between end of data sent and rts signal in milliseconds.
             It corresponds to the delay after sending data and actual release
             of the line.
           default: 0
-          maximum: 1000
+          maximum: 100
 
   rs485-rts-active-low:
     description: drive RTS low when sending (default is high).