[PATCH v3 2/7] drm/exynos: make zpos property configurable

[Marek Szyprowski]

Hello,

On 2015-12-16 14:28, Daniel Vetter wrote:
> On Wed, Dec 16, 2015 at 01:21:43PM +0100, Marek Szyprowski wrote:
>> This patch adds all infrastructure to make zpos plane property
>> configurable from userspace.
>>
>> Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
> Imo zpos should be a generic atomic property with well-defined semantics
> shared across drivers. So
> - storead (in decoded form) in drm_plane_state
> - common functions to register/attach zpos prop to a plane, with
>    full-blown kerneldoc explaining how it should work
> - generic kms igt to validate that interface
>
> One of the big things that always comes up when we talk about zpos is how
> equal zpos should be handled, and how exactly they should be sorted. I
> think for that we should have a drm function which computes a normalized
> zpos. Or the core check code should reject such nonsense.

IMHO it will be enough to state that the case of equal zpos is HW specific.
This might simplify some driver logic. For example, in case of Exynos Mixer,
equal priority (zpos) means that HW predefined order will be used, so there
is no need to normalize zpos values.

If you want I can move zpos to drm core and add a function to normalize 
zpos,
although for this particular driver normalization is not needed.

It should be quite easy to convert other drivers to use the generic zpos
property. The only problem I see is how to handle omap driver, which use
'zorder' property.

What about some other typical properties related to blending:
- global plane alpha,
- colorkey,
- alpha mode (standard or pre-multiplied) for alpha-enabled modes,
- crtc background color.

Do you also want to handle them as generic or driver-specific properties?

I plan to add support for them to Exynos Mixer and I would like to avoid
doing this twice.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland