[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 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.

Noralf.