linux-kernel - Re: [PATCH] drm/bridge: anx7625: Zero error variable when panel bridge not present

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Message-ID: <20220613173058.GA132991@elementary>
Date:   Mon, 13 Jun 2022 19:30:58 +0200
From:   José Expósito <jose.exposito89@...il.com>
To:     Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>
Cc:     Robert Foss <robert.foss@...aro.org>, kernel@...labora.com,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Maxime Ripard <maxime@...no.tech>,
        Neil Armstrong <narmstrong@...libre.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Tzung-Bi Shih <tzungbi@...gle.com>,
        Xin Ji <xji@...logixsemi.com>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: anx7625: Zero error variable when panel
 bridge not present

On Mon, Jun 13, 2022 at 12:37:05PM -0400, Nícolas F. R. A. Prado wrote:
> While parsing the DT, the anx7625 driver checks for the presence of a
> panel bridge on endpoint 1. If it is missing, pdata->panel_bridge stores
> the error pointer and the function returns successfully without first
> cleaning that variable. This is an issue since other functions later
> check for the presence of a panel bridge by testing the trueness of that
> variable.
> 
> In order to ensure proper behavior, zero out pdata->panel_bridge before
> returning when no panel bridge is found.
> 
> Fixes: 9e82ea0fb1df ("drm/bridge: anx7625: switch to devm_drm_of_get_bridge")
> Signed-off-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
> 
> ---
> 
>  drivers/gpu/drm/bridge/analogix/anx7625.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/analogix/anx7625.c b/drivers/gpu/drm/bridge/analogix/anx7625.c
> index 53a5da6c49dd..3aed4de16690 100644
> --- a/drivers/gpu/drm/bridge/analogix/anx7625.c
> +++ b/drivers/gpu/drm/bridge/analogix/anx7625.c
> @@ -1657,8 +1657,10 @@ static int anx7625_parse_dt(struct device *dev,
>  
>  	pdata->panel_bridge = devm_drm_of_get_bridge(dev, np, 1, 0);
>  	if (IS_ERR(pdata->panel_bridge)) {
> -		if (PTR_ERR(pdata->panel_bridge) == -ENODEV)
> +		if (PTR_ERR(pdata->panel_bridge) == -ENODEV) {
> +			pdata->panel_bridge = NULL;
>  			return 0;
> +		}
>  
>  		return PTR_ERR(pdata->panel_bridge);
>  	}
> -- 
> 2.36.1
> 

Thanks for spotting this error Nícolas. As you mentioned, prior to
9e82ea0fb1df the "pdata->panel_bridge" pointer was not modified
(i.e. left to NULL) on the ENODEV error branch.

I missed it during the refactor, sorry about that.