linux-kernel - Re: [PATCH v4 03/13] drm/bridge: fsl-ldb: Use clk_round

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Message-ID: <20241030-hypersonic-tremendous-tuatara-2bbeb0@houat>
Date: Wed, 30 Oct 2024 11:30:09 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Liu Ying <victor.liu@....com>
Cc: dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org, imx@...ts.linux.dev, 
	linux-arm-kernel@...ts.infradead.org, andrzej.hajda@...el.com, neil.armstrong@...aro.org, 
	rfoss@...nel.org, Laurent.pinchart@...asonboard.com, jonas@...boo.se, 
	jernej.skrabec@...il.com, maarten.lankhorst@...ux.intel.com, tzimmermann@...e.de, 
	airlied@...il.com, simona@...ll.ch, robh@...nel.org, krzk+dt@...nel.org, 
	conor+dt@...nel.org, quic_jesszhan@...cinc.com, mchehab@...nel.org, 
	shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de, 
	festevam@...il.com, catalin.marinas@....com, will@...nel.org, 
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	quic_bjorande@...cinc.com, geert+renesas@...der.be, dmitry.baryshkov@...aro.org, 
	arnd@...db.de, nfraprado@...labora.com, thierry.reding@...il.com, 
	prabhakar.mahadev-lad.rj@...renesas.com, sam@...nborg.org, marex@...x.de, biju.das.jz@...renesas.com
Subject: Re: [PATCH v4 03/13] drm/bridge: fsl-ldb: Use clk_round_rate() to
 validate "ldb" clock rate

On Mon, Oct 28, 2024 at 10:37:30AM +0800, Liu Ying wrote:
> Multiple display modes could be read from a display device's EDID.
> Use clk_round_rate() to validate the "ldb" clock rate for each mode
> in drm_bridge_funcs::mode_valid() to filter unsupported modes out.
> 
> Also, since this driver doesn't directly reference pixel clock, use
> clk_round_rate() to validate the pixel clock rate against the "ldb"
> clock if the "ldb" clock and the pixel clock are sibling in clock
> tree.  This is not done in display controller driver because
> drm_crtc_helper_funcs::mode_valid() may not decide to do the
> validation or not if multiple encoders are connected to the CRTC,
> e.g., i.MX93 LCDIF may connect with MIPI DSI controller, LDB and
> parallel display output simultaneously.
> 
> Signed-off-by: Liu Ying <victor.liu@....com>
> ---
> Note that this patch depends on a patch in shawnguo/imx/fixes:
> https://patchwork.kernel.org/project/linux-arm-kernel/patch/20241017031146.157996-1-marex@denx.de/

I still believe that the root cause of this issue is your clock tree and
driver setup, and since I've asked for explanations and didn't get any,
I don't really see how we can move forward here.

Maxime

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