[PATCH 0/3] drm/exynos: add support for dynamic zpos in DECON and FIMD

[Inki Dae]

Hi Andrzej,

18. 12. 10. 오후 4:35에 Andrzej Hajda 이(가) 쓴 글:
> Hi Inki,
> 
> On 10.12.2018 03:25, Inki Dae wrote:
>> Hi Andrzej,
>>
>> 18. 12. 6. 오후 6:38에 Andrzej Hajda 이(가) 쓴 글:
>>> Hi Inki,
>>>
>>> This small patchset adds dynamic zpos support for DECON and FIMD.
>> This patch will allow user space to change zpos. However, DECON and FIMD devices have fixed priority of HW overlays.
>> This would mean that zpos change by user space doesn't guarantee correct HW overlay priority.
>>
>> Why do you want to support mutable zpos?
> 
> 
> Practically you have patches which proves it works, you can see that
> changing zpos value results in adequate change in displayed image.
> 
> Conceptually it is just a matter of disconnecting hardware windows
> present in DECON and FIMD from DRM planes which are software entities.
> 
> You can reason about it this way:
> 
> - drm plane is a framebuffer plus informations how it should be
> transformed/displayed on DECON/FIMD,
> 
> - hw window in DECON/FIMD is just a channel through which plane is send
> to the display.
> 
> DECON and FIMD has fixed hw windows order - windows with lower numbers
> are displayed below windows with higher number. To display planes in
> given z-order you just need to send them via windows with appropriate
> index - farthest plane should go always via win0, closer one via win1,
> ..., till the last plane.
> 
> So for example if you have three planes and want to display them in
> following order (first one farthest, last one closest):
> 
> plane2, plane1, plane3
> 
> you should map them to planes as follow:
> 
> plane2 -> win0, plane1 -> win1, plane3 -> win2
> 
> then for example plane2 is disabled, we will have following mapping:
> 
> plane1 -> win0, plane3 -> win1, win2 - disabled

Plane1 is displayed below Plane3.

> 
> then if you change zorder of planes to: plane3, plane1:
> 
> plane3 -> win0, plane1 -> win1

Plane3 is displayed below Plane1 because DECON/FIMD HW aren't able to change HW overlay priroty.
However, user space wanted that Plane1 is displayed below Plane3. Like this, zpos change by user space doesn't guarantee correct HW overlay priority.
And there is no any reason to change zpos in user space excepting Mixer device which supports HW overlay priority change.
In fact, we supported mutable zpos before but changed it to immutable with same reason.

Lastly, your patch made real user broken.

Thanks,
Inki Dae

> 
> 
> As you see there is no relation between plane number and window number,
> but window number is equal to plane's position in zpos-ordered list of
> planes and this is exact value of normalized_zpos field in drm_plane_state.
> 
> 
> I hope this extended explanation will clarify things.
> 
> 
> Regards
> 
> Andrzej
> 
> 
> 
>>
>> Thanks,
>> Inki Dae
>>
>>> It was tested on tm2 and trats2.
>>>
>>> Regards
>>> Andrzej
>>>
>>>
>>> Andrzej Hajda (3):
>>>   drm/exynos/decon5433: add dynamic zpos support
>>>   drm/exynos/fimd: create local helper for disabling hardware window
>>>   drm/exynos/fimd: add dynamic zpos support
>>>
>>>  drivers/gpu/drm/exynos/exynos5433_drm_decon.c | 23 +++++-----
>>>  drivers/gpu/drm/exynos/exynos_drm_fimd.c      | 42 ++++++++-----------
>>>  2 files changed, 29 insertions(+), 36 deletions(-)
>>>
>>
> 
> 
>