[PATCH] drm: rcar-du: add modifiers support

[Esaki Tomohito]

Hi Daniel-san,

On 2021/11/30 22:20, Daniel Stone wrote:
> On Tue, 30 Nov 2021 at 08:44, Esaki Tomohito <etom at igel.co.jp> wrote:
>> On 2021/11/18 23:05, Laurent Pinchart wrote:
>>> On Thu, Nov 18, 2021 at 01:02:11PM +0000, Daniel Stone wrote:
>>>> Laurent's concern is that the DRM core should handle this rather than
>>>> open-coding in every driver, which I agree with. Some drivers (e.g.
>>>> radeon, maybe legacy NV?) do not support modifiers, and _also_ do
>>>> magic inference of the actual layout of the underlying buffer.
>>>> However, these drivers are legacy and we do not accept any new
>>>> addition of inferring layout without modifiers.
>>>>
>>>> I think the best way forward here is:
>>>>     - add a new mode_config.cannot_support_modifiers flag, and enable
>>>> this in radeon (plus any other drivers in the same boat)
>>>
>>> Is there an easy way to identify the drivers that need this ?
>>
>> Should I find a driver that has not use drm_plane_funcs?
> 
> I don't think there's a good way to systematically audit it. The only
> two I know are radeon (i.e. pre-amdgpu) and nouveau (pre-nv50), both
> of which pass no modifiers to drm_universal_plane_init(), but do have
> magic back channels to communicate tiling information. If anyone knows
> of any others, well, I guess we'll find out. :)
Thanks for the information.
I checked the driver code with the tiling keyword, and it seems that 
these are the only two drivers that require cannot_support_modifiers.
I will start creating patches for these two drivers first.

-- 
Best Regards
Tomohito Esaki