linux-kernel - Re: [PATCH] drm/sun4i: Fix blend route/enable register corruption for DE2.0/DE3.0

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Date:   Mon, 30 May 2022 15:22:32 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Roman Stratiienko <r.stratiienko@...il.com>
Cc:     wens@...e.org, jernej.skrabec@...il.com, airlied@...ux.ie,
        daniel@...ll.ch, samuel@...lland.org,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org, megi@....cz,
        Roman Stratiienko <roman.o.stratiienko@...ballogic.com>
Subject: Re: [PATCH] drm/sun4i: Fix blend route/enable register corruption
 for DE2.0/DE3.0

Hi Roman,

On Wed, May 25, 2022 at 11:54:45AM +0000, Roman Stratiienko wrote:
> By this commit 2 related issues are solved:
> 
>   Issue #1. Corruption in blend route/enable register:
> 
> Register corruption happens after using old_state->zpos to disable layer
> state. Blend route/enable registers are shared with other layers
> and other layers may have already assigned this PIPE to valid value.
> 
> Solution: Do not use old_state->zpos to disable the plane pipe in
> blend registers.
> 
>   Issue #2. Remove disabled layer from blend route/enable registers:
> 
> Since sun4i/drm are using normalized_zpos, .atomic_update() will setup
> blend route/enable pipes starting from PIPE0 to PIPEX, where X+1 is a
> number of layers used by the CRTC in this frame.
> 
> Remaining pipes (PIPE[X+1] - PIPE[MAX]) can have old data that MUST be
> updated.
> 
> new_state->normalized_zpos can't be used, since drm helpers won't update
> it for disabled planes.
> 
> Solution:
> 
> 1. Track the number of total used planes for crtc.
> 2. Use this number instead of zpos to disable unused blend pipes.
> 
> Signed-off-by: Roman Stratiienko <roman.o.stratiienko@...ballogic.com>

If there's two issues, and two solutions, it should be two patches.

Maxime