linux-kernel - Re: [PATCH] drm/mediatek: hdmi: Perform NULL pointer check for mtk_hdmi

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Date:   Mon, 13 Dec 2021 11:02:40 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     chunkuang.hu@...nel.org
Cc:     p.zabel@...gutronix.de, airlied@...ux.ie, daniel@...ll.ch,
        matthias.bgg@...il.com, dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        dafna.hirschfeld@...labora.com, kernel@...labora.com
Subject: Re: [PATCH] drm/mediatek: hdmi: Perform NULL pointer check for
 mtk_hdmi_conf

Il 28/10/21 09:43, AngeloGioacchino Del Regno ha scritto:
> In commit 41ca9caaae0b ("drm/mediatek: hdmi: Add check for CEA modes only")
> a check for CEA modes was added to function mtk_hdmi_bridge_mode_valid()
> in order to address possible issues on MT8167; moreover, with commit
> c91026a938c2 ("drm/mediatek: hdmi: Add optional limit on maximal HDMI mode clock")
> another similar check was introduced.
> 
> Unfortunately though, at the time of writing, MT8173 does not provide
> any mtk_hdmi_conf structure and this is crashing the kernel with NULL
> pointer upon entering mtk_hdmi_bridge_mode_valid(), which happens as
> soon as a HDMI cable gets plugged in.
> 
> To fix this regression, add a NULL pointer check for hdmi->conf in the
> said function, restoring HDMI functionality and avoiding NULL pointer
> kernel panics.
> 
> Fixes: 41ca9caaae0b ("drm/mediatek: hdmi: Add check for CEA modes only")
> Fixes: c91026a938c2 ("drm/mediatek: hdmi: Add optional limit on maximal HDMI mode clock")
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> ---
>   drivers/gpu/drm/mediatek/mtk_hdmi.c | 12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_hdmi.c b/drivers/gpu/drm/mediatek/mtk_hdmi.c
> index 5838c44cbf6f..3196189429bc 100644
> --- a/drivers/gpu/drm/mediatek/mtk_hdmi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_hdmi.c
> @@ -1224,12 +1224,14 @@ static int mtk_hdmi_bridge_mode_valid(struct drm_bridge *bridge,
>   			return MODE_BAD;
>   	}
>   
> -	if (hdmi->conf->cea_modes_only && !drm_match_cea_mode(mode))
> -		return MODE_BAD;
> +	if (hdmi->conf) {
> +		if (hdmi->conf->cea_modes_only && !drm_match_cea_mode(mode))
> +			return MODE_BAD;
>   
> -	if (hdmi->conf->max_mode_clock &&
> -	    mode->clock > hdmi->conf->max_mode_clock)
> -		return MODE_CLOCK_HIGH;
> +		if (hdmi->conf->max_mode_clock &&
> +		    mode->clock > hdmi->conf->max_mode_clock)
> +			return MODE_CLOCK_HIGH;
> +	}
>   
>   	if (mode->clock < 27000)
>   		return MODE_CLOCK_LOW;
> 

Hello, friendly ping!

Can I please get a review (or merge) of this commit?

This is an important fix for a null pointer KP and restores HDMI functionality.

Thanks,
- Angelo