Re: [PATCH 03/11] drm: of: drm_of_find_panel_or_bridge: prioritize the bridge, not the panel

[Luca Ceresoli]

Hi Maxime,

On Mon Aug 24, 2026 at 10:16 AM CEST, Maxime Ripard wrote:
> On Mon, Aug 17, 2026 at 02:23:05PM +0200, Luca Ceresoli wrote:
>> > That being said, if we do create a panel_bridge for every panel, why do
>> > we still need drm_of_find_panel_or_bridge()? We'll only really need
>> > of_drm_find_bridge(), no?
>>
>> Yes, in the long term we can get rid of drm_of_find_panel_or_bridge(), but
>> not in the short term due to the above mentioned drivers, and others which
>> use it in "creative" ways.
>>
>> The point is about the transition. This patch was an attempt to convert at
>> once all the many drivers which use the most common pattern:
>>
>>       | drm_of_find_panel_or_bridge(..., &panel, &bridge);
>>       | if (panel)
>>       |     bridge = drm_panel_bridge_add();
>>
>> to then fix manually the remaining drivers (patches 6-11).
>>
>> But this approach doesn't fly due to the legacy users of
>> drm_of_find_panel_or_bridge() as mentioned above.
>>
>> So what about this other approach instead:
>>
>>  1. leave drm_of_find_panel_or_bridge() as is (it's already deprecated anyway)
>>  2. keep patch 5 (which "breaks" mayt drivers which would create an additional
>>     panel_bridge)
>>  3. perhaps add a warning when an additional bridge is created for the
>>     some panel
>>  4. *in the same series*, manually convert *all* drivers to use
>>     of_drm_find_bridge() or of_drm_get_bridge_by_endpoint() -- like patches
>>     6-11, but done on all drivers
>>  5. apply the series atomically, because it wouldn't be bisectable between
>>     items 2 and 4
>>
>> Your opinion?
>
> If we look at the drivers causing us troubles, fsl-ldb, samsung-dsim,
> tc358767 and waveshare-dsi can be converted directly to
> devm_drm_of_get_bridge().
>
> mcde-dsi is a mess and would be hard to fix indeed, but since it's the
> only really troublesome one, maybe we can just duplicate the code in the
> driver and drop / rewrite the common code however we see fit.

Note there are many more drivers than those converted by patches 6-11 of
this series (see cover letter). So it would be a lot more work.

But based on your reply I assume you approve the 5-point plan above. Please
let me know if my understanding is incorrect.

Also note my plan is to try converting all drivers, definitely removing all
calls to drm_panel_bridge_add() and variants but not necessarily
drm_of_find_panel_or_bridge(), which then might exist for a longer
time. I'll see how things go as I look at drivers one my one.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com