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Date:   Mon, 30 May 2022 15:22:32 +0200
From:   Maxime Ripard <maxime@cerno.tech>
To:     Roman Stratiienko <r.stratiienko@gmail.com>
Cc:     wens@csie.org, jernej.skrabec@gmail.com, airlied@linux.ie,
        daniel@ffwll.ch, samuel@sholland.org,
        dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev,
        linux-kernel@vger.kernel.org, megi@xff.cz,
        Roman Stratiienko <roman.o.stratiienko@globallogic.com>
Subject: Re: [PATCH] drm/sun4i: Fix blend route/enable register corruption
 for DE2.0/DE3.0
Message-ID: <20220530132232.himfp7ubiacbmkpx@penduick>
References: <20220525115445.93500-1-roman.o.stratiienko@globallogic.com>
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Hi Roman,

On Wed, May 25, 2022 at 11:54:45AM +0000, Roman Stratiienko wrote:
> By this commit 2 related issues are solved:
>=20
>   Issue #1. Corruption in blend route/enable register:
>=20
> 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.
>=20
> Solution: Do not use old_state->zpos to disable the plane pipe in
> blend registers.
>=20
>   Issue #2. Remove disabled layer from blend route/enable registers:
>=20
> 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.
>=20
> Remaining pipes (PIPE[X+1] - PIPE[MAX]) can have old data that MUST be
> updated.
>=20
> new_state->normalized_zpos can't be used, since drm helpers won't update
> it for disabled planes.
>=20
> Solution:
>=20
> 1. Track the number of total used planes for crtc.
> 2. Use this number instead of zpos to disable unused blend pipes.
>=20
> Signed-off-by: Roman Stratiienko <roman.o.stratiienko@globallogic.com>

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

Maxime