linux-kernel - Re: [PATCH] drm/bridge: anx7625: Fix EDID block size at drm_edid

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Message-ID: <45be2cab-d6a3-4ff8-b66e-2424a74328f6@quicinc.com>
Date: Mon, 3 Nov 2025 16:04:27 +0530
From: Ayushi Makhija <quic_amakhija@...cinc.com>
To: Xin Ji <xji@...logixsemi.com>, 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>,
        "Maarten
 Lankhorst" <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard
	<mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie
	<airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Jani Nikula
	<jani.nikula@...el.com>,
        Dmitry Baryshkov
	<dmitry.baryshkov@....qualcomm.com>,
        Konrad Dybcio
	<konrad.dybcio@....qualcomm.com>,
        <quic_rajeevny@...cinc.com>
CC: <bliang@...logixsemi.com>, <qwen@...logixsemi.com>,
        <treapking@...omium.org>,
        <jason-jh.lin@...iatek.corp-partner.google.com>,
        <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/bridge: anx7625: Fix EDID block size at
 drm_edid_alloc() calling

On 8/8/2025 12:16 PM, Xin Ji wrote:
> Since DRM validates the all of EDID blocks, allocates drm_edid data
> structure based on the actually block count returned by the sink
> monitor at drm_edid_alloc() calling.
> 
> Fixes: 7c585f9a71aa ("drm/bridge: anx7625: use struct drm_edid more")
> 
> Signed-off-by: Xin Ji <xji@...logixsemi.com>
> ---
>  drivers/gpu/drm/bridge/analogix/anx7625.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/analogix/anx7625.c b/drivers/gpu/drm/bridge/analogix/anx7625.c
> index c0ad8f59e483..4b5a74e9785e 100644
> --- a/drivers/gpu/drm/bridge/analogix/anx7625.c
> +++ b/drivers/gpu/drm/bridge/analogix/anx7625.c
> @@ -1801,7 +1801,7 @@ static const struct drm_edid *anx7625_edid_read(struct anx7625_data *ctx)
>  		return NULL;
>  	}
>  
> -	ctx->cached_drm_edid = drm_edid_alloc(edid_buf, FOUR_BLOCK_SIZE);
> +	ctx->cached_drm_edid = drm_edid_alloc(edid_buf, edid_num * EDID_LENGTH);
>  	kfree(edid_buf);
>  
>  out:

I applied https://lore.kernel.org/all/20250808064613.2623732-1-xji@analogixsemi.com/ on linux-next (next-20250929),
tested on QCS9100 RIDE SX platform.

Before this patch, the ANX7625 bridge driver allocated drm_edid with a fixed 512 bytes (FOUR_BLOCK_SIZE),
while the connected monitor provides only 256 bytes of EDID (2 blocks; EDID_LENGTH = 128 bytes per block)
(It could vary depending on the number of edid blocks supported by the monitor). This mismatch caused
drm_edid_valid() to fail and the system to boot into a fail safe mode.

With this patch, the allocation uses edid_num * EDID_LENGTH, matching the actual number of EDID blocks from
the monitor, and the issue is no longer reproducible.

Tested-by: Ayushi Makhija <quic_amakhija@...cinc.com>

Thanks,
Ayushi