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

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Message-ID: <65fc8309-a3b8-4323-9431-8ab77f571d49@nxp.com>
Date: Tue, 19 Nov 2024 10:16:52 +0800
From: Liu Ying <victor.liu@....com>
To: Maxime Ripard <mripard@...nel.org>
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,
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 Laurent.pinchart@...asonboard.com, jonas@...boo.se,
 jernej.skrabec@...il.com, maarten.lankhorst@...ux.intel.com,
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 krzk+dt@...nel.org, conor+dt@...nel.org, quic_jesszhan@...cinc.com,
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 prabhakar.mahadev-lad.rj@...renesas.com, sam@...nborg.org, marex@...x.de,
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Subject: Re: [PATCH v4 03/13] drm/bridge: fsl-ldb: Use clk_round_rate() to
 validate "ldb" clock rate

On 10/31/2024, Liu Ying wrote:
> Hi Maxime,
> 
> On 10/30/2024, Maxime Ripard wrote:
>> 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.
> 
> Since you asked for a description at *somewhere* in another thread[1],
> can you please suggest a place where this could happen?

I have written a description in the cover letter of this patch series(v7):

https://patchwork.freedesktop.org/series/139266/#rev7

If you don't mind, please provide review comments there, thanks.

> 
> [1] https://lore.kernel.org/imx/47d92ae0-c71a-4c18-9ad7-432c0f70a31f@nxp.com/T/#m587e6a25bdab542d5d99abbf01caaca89495b1d5
> 
>>
>> Maxime
> 

-- 
Regards,
Liu Ying