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

[Marek Vasut]

On 4/4/22 18:01, Rob Herring wrote:
> On Sat, Apr 02, 2022 at 07:55:59PM +0200, Marek Vasut wrote:
>> 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 ? Rob ?
> 
> Yes, it can be fixed. And the binding, not the kernel, is the place to
> enforce it being mandatory IMO.

All right, I sent 1/3 separately with Fixes: tag, so it can be applied .