[RFC PATCH 1/3] drm: Introduce color fill properties for drm plane

[Jessica Zhang]

On 11/9/2022 5:59 AM, Daniel Vetter wrote:
> On Wed, Nov 09, 2022 at 04:53:45PM +0300, Dmitry Baryshkov wrote:
>> On 09/11/2022 16:52, Daniel Vetter wrote:
>>> On Tue, Nov 08, 2022 at 06:25:29PM +0000, Simon Ser wrote:
>>>> On Saturday, October 29th, 2022 at 13:23, Dmitry Baryshkov <dmitry.baryshkov at linaro.org> wrote:
>>>>
>>>>> On 29/10/2022 01:59, Jessica Zhang wrote:
>>>>>
>>>>>> Add support for COLOR_FILL and COLOR_FILL_FORMAT properties for
>>>>>> drm_plane. In addition, add support for setting and getting the values
>>>>>> of these properties.
>>>>>>
>>>>>> COLOR_FILL represents the color fill of a plane while COLOR_FILL_FORMAT
>>>>>> represents the format of the color fill. Userspace can set enable solid
>>>>>> fill on a plane by assigning COLOR_FILL to a uint64_t value, assigning
>>>>>> the COLOR_FILL_FORMAT property to a uint32_t value, and setting the
>>>>>> framebuffer to NULL.
>>>>>
>>>>> I suppose that COLOR_FILL should override framebuffer rather than
>>>>> requiring that FB is set to NULL. In other words, if color_filL_format
>>>>> is non-zero, it would make sense to ignore the FB. Then one can use the
>>>>> color_fill_format property to quickly switch between filled plane and
>>>>> FB-backed one.
>>>>
>>>> That would be inconsistent with the rest of the KMS uAPI. For instance,
>>>> the kernel will error out if CRTC has active=0 but a connector is still
>>>> linked to the CRTC. IOW, the current uAPI errors out if the KMS state
>>>> is inconsistent.
>>>
>>> So if the use-case here really is to solid-fill a plane (and not just
>>> provide a background color for the crtc overall), then I guess we could
>>> also extend addfb to make that happen. We've talked in the past about
>>> propertery-fying framebuffer objects, and that would sort out this uapi
>>> wart. And I agree the color fill vs PLANE_ID issue is a bit ugly at least.
>>>
>>> But if the use-cases are all background color then just doing the crtc
>>> background color would be tons simpler (and likely also easier to support
>>> for more hardware).
>>
>> No. The hardware supports multiple color-filled planes, which do not have to
>> cover the whole CRTC.
> 
> The use case here means the userspace use-case. What the hw can do on any
> given chip kinda doesnt matter, which is why I'm asking. KMD uapi is not
> meant to reflect 100% exactly what a specific chip can do, but instead:
> - provide features userspace actually needs. If you want per-plane fill,
>    you need userspace that makes use of per-plane fill, and if all you have
>    is crtc background, then that's it.

Hey Daniel,

The userspace use case we're trying to support is the Android HWC 
SOLID_FILL hint here [1], which is specifying per-plane fill.

Thanks,

Jessica Zhang

[1] 
https://android.googlesource.com/platform/hardware/interfaces/+/refs/heads/master/graphics/composer/aidl/android/hardware/graphics/composer3/Composition.aidl#52

> - we should create uapi with an eye towards what's actually possible on a
>    reasonable set of drivers and hw. Sometimes that means a slightly more
>    restricted set so that it's possible to implement in more places,
>    especially if that restricted feature set still gets the job done for
>    userspace.
> 
> Cheers, Daniel
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch