linux-kernel - RE: [PATCH v2] drm/bridge: panel: Fix device link for DRM_BRIDGE_ATTACH_NO

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Date:   Wed, 20 Sep 2023 09:30:02 +0000
From:   Ying Liu <victor.liu@....com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        "andrzej.hajda@...el.com" <andrzej.hajda@...el.com>
CC:     "neil.armstrong@...aro.org" <neil.armstrong@...aro.org>,
        "rfoss@...nel.org" <rfoss@...nel.org>,
        "Laurent.pinchart@...asonboard.com" 
        <Laurent.pinchart@...asonboard.com>,
        "jonas@...boo.se" <jonas@...boo.se>,
        "jernej.skrabec@...il.com" <jernej.skrabec@...il.com>,
        "airlied@...il.com" <airlied@...il.com>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel@...labora.com" <kernel@...labora.com>,
        "ehristev@...labora.com" <ehristev@...labora.com>,
        "wenst@...omium.org" <wenst@...omium.org>
Subject: RE: [PATCH v2] drm/bridge: panel: Fix device link for
 DRM_BRIDGE_ATTACH_NO_CONNECTOR

On Wednesday, September 20, 2023 4:27 PM AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com> wrote:
> When external bridges are attached with
> DRM_BRIDGE_ATTACH_NO_CONNECTOR,
> the panel bridge may also get the same flag, but in the .attach()
> callback for the panel bridge a device link is added only when this
> flag is not present; To make things worse, the .detach() callback
> tries to delete the device link unconditionally and without checking
> if it was created in the first place, crashing the kernel with a NULL
> pointer kernel panic upon calling panel_bridge_detach().
> 
> Fix that by moving the device_link_add() call before checking if the
> DRM_BRIDGE_ATTACH_NO_CONNECTOR flag is present.
> 
> Fixes: 199cf07ebd2b ("drm/bridge: panel: Add a device link between drm
> device and panel device")
> Signed-off-by: AngeloGioacchino Del Regno
> <angelogioacchino.delregno@...labora.com>
> ---
> 
> Changes in v2:
>  - Added device_link_del() for (!bridge->encoder) error condition
> 
>  drivers/gpu/drm/bridge/panel.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)

Reviewed-by: Liu Ying <victor.liu@....com>