linux-kernel - Re: [PATCH] drm: bridge: fsl-ldb: fixup mode on freq mismatch

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Message-ID: <9cc55af202690bad0616bee76430133d@vosn.de>
Date: Mon, 02 Dec 2024 18:03:16 +0100
From: Nikolaus Voss <nv@...n.de>
To: Marek Vasut <marex@...x.de>
Cc: Liu Ying <victor.liu@....nxp.com>, Alexander Stein
 <alexander.stein@...tq-group.com>, Liu Ying <victor.liu@....com>, Luca
 Ceresoli <luca.ceresoli@...tlin.com>, Fabio Estevam <festevam@...x.de>,
 Andrzej Hajda <andrzej.hajda@...el.com>, Neil Armstrong
 <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, Laurent
 Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman
 <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, David Airlie
 <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, Miquel Raynal
 <miquel.raynal@...tlin.com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, nikolaus.voss@...g-streit.com
Subject: Re: [PATCH] drm: bridge: fsl-ldb: fixup mode on freq mismatch

On 02.12.2024 13:56, Marek Vasut wrote:
> On 12/2/24 7:32 AM, Liu Ying wrote:
>> On 11/27/2024, Nikolaus Voss wrote:
>>> LDB clock has to be a fixed multiple of the pixel clock.
>>> As LDB and pixel clock are derived from different clock sources
>>> (at least on imx8mp), this constraint cannot be satisfied for
>>> any pixel clock, which leads to flickering and incomplete
>>> lines on the attached display.
>>> 
>>> To overcome this, check this condition in mode_fixup() and
>>> adapt the pixel clock accordingly.
>>> 
>>> Cc: <stable@...r.kernel.org>
>> 
>> It looks like stable is not effectively Cc'ed.
>> Need a Fixes tag?
> Isn't this fix effectively superseded by series
> 
> [PATCH 0/5] clk: Fix simple video pipelines on i.MX8
> 
> ?

Maybe. I wasn't aware of the series. Looking at it, the change is
rather complex and not suitable for the stable series.

My intention was to get a simple fix which doesn't potentially
break anything. It wouldn't even break the patch series you mentioned.

-- 
Nikolaus Voss