[RFC][PATCH 2/3] drm/modes: Make width-mm/height-mm mandatory in of_get_drm_panel_display_mode()

[Noralf Trønnes]

Den 02.04.2022 19.55, skrev Marek Vasut:
> On 4/2/22 19:08, Noralf Trønnes wrote:
>>
>>
>> Den 02.04.2022 18.39, skrev Marek Vasut:
>>> On 4/2/22 09:45, Noralf Trønnes wrote:
>>>>
>>>>
>>>> Den 02.04.2022 06.28, skrev Marek Vasut:
>>>>> On 4/2/22 05:19, Laurent Pinchart wrote:
>>>>>> On Fri, Apr 01, 2022 at 10:36:24PM +0200, Marek Vasut wrote:
>>>>>>> On 4/1/22 20:46, Laurent Pinchart wrote:
>>>>>>>> On Fri, Apr 01, 2022 at 06:37:54PM +0200, Marek Vasut wrote:
>>>>>>>>> Make the width-mm/height-mm panel properties mandatory in
>>>>>>>>> of_get_drm_panel_display_mode(), print error message and
>>>>>>>>> return -ve in case these DT properties are not present.
>>>>>>>>> This is needed to correctly report panel dimensions.
>>>>>>>>
>>>>>>>> Can we guarantee this won't cause a regression ?
>>>>>>>
>>>>>>> For the upstream DTs, I think we can.
>>>>>>> For downstream DTs, we cannot know.
>>>>>>
>>>>>> Are there users of this function whose DT bindings don't require the
>>>>>> width-mm and height-mm properties ?
>>>>>
>>>>> There is literally one user of this function upstream:
>>>>> drivers/gpu/drm/tiny/panel-mipi-dbi.c
>>>>
>>>> Yes, the function was added for that driver since it was so generic in
>>>> nature. What about adding an argument to
>>>> of_get_drm_panel_display_mode()
>>>> that tells if the properties are mandatory or not?
>>>
>>> Sure, we can do that, but maybe the question here is even bigger than
>>> this series.
>>>
>>> Should every panel set mandatory width_mm/height_mm so e.g. the user
>>> space can infer DPI from it and set up scaling accordingly, or should
>>> width_mm/height_mm be optional ?
>>>
>>> I think width_mm/height_mm should be mandatory for all panels.
>>>
>>> Thoughts ?
>>
>> If this had come up during the review of the driver I would have no
>> problem making it mandatory. It makes sense for DPI. Maybe it's possible
>> to get around the ABI break by getting in a change through -fixes before
>> 5.18 is released? I'm fine with that.
> 
> Well that's awesome, the dbi-spi.yaml didn't land in any kernel release
> yet, so we still have a chance to fix it ?

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