linux-kernel - Re: [PATCH 3/3] drm/sun4i: Fix layer zpos change/atomic modesetting

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Date: Wed, 21 Feb 2024 14:45:20 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Ondřej Jirman <megi@....cz>
Cc: Chen-Yu Tsai <wens@...e.org>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Samuel Holland <samuel@...lland.org>, 
	dri-devel@...ts.freedesktop.org, linux-arm-kernel@...ts.infradead.org, 
	linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] drm/sun4i: Fix layer zpos change/atomic modesetting

Hi,

On Fri, Feb 16, 2024 at 08:04:26PM +0100, Ondřej Jirman wrote:
> From: Ondrej Jirman <megi@....cz>
> 
> Identical configurations of planes can lead to different (and wrong)
> layer -> pipe routing at HW level, depending on the order of atomic
> plane changes.
> 
> For example:
> 
> - Layer 1 is configured to zpos 0 and thus uses pipe 0. No other layer
>   is enabled. This is a typical situation at boot.
> 
> - When a compositor takes over and layer 3 is enabled,
>   sun8i_ui_layer_enable() will get called with old_zpos=0 zpos=1, which
>   will lead to incorrect disabling of pipe 0 and enabling of pipe 1.
> 
> What happens is that sun8i_ui_layer_enable() function may disable
> blender pipes even if it is no longer assigned to its layer.
> 
> To correct this, move the routing setup out of individual plane's
> atomic_update into crtc's atomic_update, where it can be calculated
> and updated all at once.
> 
> Remove the atomic_disable callback because it is no longer needed.
> 
> Signed-off-by: Ondrej Jirman <megi@....cz>

I don't have enough knowledge about the mixers code to comment on your
patch, so I'll let Jernej review it. However, this feels to me like the
pipe assignment is typically the sort of things that should be dealt
with device-wide, and in atomic_check.

If I'm talking non-sense, it would be great to mention at least why that
can't be an option in the commit log.

Maxime

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