Re: [RESEND][PATCH v3 0/4] drm/ast: Disable HW cursor when switching modes

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Sep 14, 2020 at 09:22:32AM +0200, Thomas Zimmermann wrote:
> Since converting the ast driver to atomic modesetting, modesetting
> occationally locks up the graphics hardware and turns the display
> permanently dark. This happens once or twice per 10 mode switches.
> Investigation shows that the ast hardware presumably requires the HW
> cursor to be disabled while the modeswitch takes place.
> 
> This patchset fixes the problem by disabling planes before programming
> the CRTC mode. After the switch, the planes gets re-enabled if they were
> enabled before. For mere pageflip operations, nothing changes.
> 
> Patches #1 makes format changes work as intended: format registers are
> only updated if necessary. They used to be changed on each pageflip.
> 
> Patches #2 to #4 change the modesetting logic such that planes will be
> disabled with the CRTC, then the CRTC's new mode is being programmed,
> and finally planes are reenabled. The primary plane is enabled before
> the cursor plane. With this setup, the cursor plane always has a valid
> mode and framebuffer available.
> 
> Tested on AST2100 HW. The issue is not 100% reproducible, but does not
> show up after applying the patchset. I think the problem has been fixed.
> 
> Thomas Zimmermann (4):
>   drm/ast: Set format registers in primary plane's update
>   drm/ast: Disable planes while switching display modes
>   drm/ast: Program display mode in CRTC's atomic_enable()
>   drm/ast: Enable CRTC before planes

Ofc I can't check all the details, but I think this is using atomic
helpers a lot more like they're intended to be used. So definitely a good
cleanup. On the series:

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
>  drivers/gpu/drm/ast/ast_drv.h  |   2 +
>  drivers/gpu/drm/ast/ast_mode.c | 103 ++++++++++++++++++++-------------
>  2 files changed, 64 insertions(+), 41 deletions(-)
> 
> --
> 2.28.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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