linux-kernel - Re: [PATCH] drm/sun4i: tcon: Set RGB DCLK min. divider based on hardware model

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Date:   Tue, 7 Jan 2020 16:06:25 +0100
From:   Maxime Ripard <mripard@...nel.org>
To:     Chen-Yu Tsai <wens@...nel.org>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Chen-Yu Tsai <wens@...e.org>, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] drm/sun4i: tcon: Set RGB DCLK min. divider based on
 hardware model

On Tue, Jan 07, 2020 at 03:01:13PM +0800, Chen-Yu Tsai wrote:
> From: Chen-Yu Tsai <wens@...e.org>
>
> In commit 0b8e7bbde5e7 ("drm/sun4i: tcon: Set min division of TCON0_DCLK
> to 1.") it was assumed that all TCON variants support a minimum divider
> of 1 if only DCLK was used.
>
> However, the oldest generation of hardware only supports minimum divider
> of 4 if only DCLK is used. If a divider of 1 was used on this old
> hardware, some scrolling artifact would appear. A divider of 2 seemed
> OK, but a divider of 3 had artifacts as well.
>
> Set the minimum divider when outputing to parallel RGB based on the
> hardware model, with a minimum of 4 for the oldest (A10/A10s/A13/A20)
> hardware, and a minimum of 1 for the rest. A value is not set for the
> TCON variants lacking channel 0.
>
> This fixes the scrolling artifacts seen on my A13 tablet.
>
> Fixes: 0b8e7bbde5e7 ("drm/sun4i: tcon: Set min division of TCON0_DCLK to 1.")
> Cc: <stable@...r.kernel.org> # 5.4.x
> Signed-off-by: Chen-Yu Tsai <wens@...e.org>

Applied, thanks

Maxime

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