[PATCH v4] drm/omap: plane zpos/zorder management improvements

[Tomi Valkeinen]

On 08/01/18 10:20, Peter Ujfalusi wrote:
> Hi Laurent,
> 
> On 2018-01-05 16:04, Laurent Pinchart wrote:
>> Hi Peter,
>>
>> Thank you for the patch and sorry for the late review.
>>
>> On Friday, 5 January 2018 13:30:37 EET Peter Ujfalusi wrote:
>>> Use the plane index as default zpos for all planes. Even if the
>>> application is not setting zpos/zorder explicitly we will have unique zpos
>>> for each plane.
>>>
>>> Enforce that all planes must have unique zpos on the given crtc.
>>
>> Could you explain the rationale for that in the commit message, what's wrong 
>> with duplicate zpos values ?
> 
> Planes with identical zpos is only 'valid' _if_ they are not
> overlapping, if they do overlap then it is - imho - not a valid
> configuration anyway (which one should be on top?).

For DSS it's clear. It is an invalid HW configuration to have multiple
planes with the same zpos in the same crtc. I believe the result is
undefined HW behavior.

So we either return an error, or the kernel normalizes zpos'es.
Normalizing means the kernel is guessing what the end result should be,
so I like error better.

 Tomi

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