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

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Message-ID: <6cde344a-9e93-07b0-862b-aa401e6c64fb@collabora.com>
Date:   Wed, 20 Sep 2023 10:24:39 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Ying Liu <victor.liu@....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] drm/bridge: panel: Fix device link for
 DRM_BRIDGE_ATTACH_NO_CONNECTOR

Il 19/09/23 03:45, Ying Liu ha scritto:
> Hi Angelo,
> 
> Thank you for the patch.
> 
> On Monday, September 18, 2023 11:01 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>
>> ---
>>   drivers/gpu/drm/bridge/panel.c | 16 ++++++++--------
>>   1 file changed, 8 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/panel.c
>> b/drivers/gpu/drm/bridge/panel.c
>> index e00d2e94c751..8c507dfd589e 100644
>> --- a/drivers/gpu/drm/bridge/panel.c
>> +++ b/drivers/gpu/drm/bridge/panel.c
>> @@ -67,14 +67,6 @@ static int panel_bridge_attach(struct drm_bridge
>> *bridge,
>>   	struct drm_device *drm_dev = bridge->dev;
>>   	int ret;
>>
>> -	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
>> -		return 0;
>> -
>> -	if (!bridge->encoder) {
>> -		DRM_ERROR("Missing encoder\n");
>> -		return -ENODEV;
>> -	}
>> -
>>   	panel_bridge->link = device_link_add(drm_dev->dev, panel->dev,
>>   					     DL_FLAG_STATELESS);
>>   	if (!panel_bridge->link) {
>> @@ -83,6 +75,14 @@ static int panel_bridge_attach(struct drm_bridge
>> *bridge,
>>   		return -EINVAL;
>>   	}
>>
>> +	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
>> +		return 0;
>> +
>> +	if (!bridge->encoder) {
>> +		DRM_ERROR("Missing encoder\n");
> 
> Shouldn't the device link be deleted in case of error?
> 

Whoops! Yes, that's right. I'm sending a v2 right now.

Thanks!
Angelo

> Regards,
> Liu Ying
> 
>> +		return -ENODEV;
>> +	}
>> +
>>   	drm_connector_helper_add(connector,
>>   				 &panel_bridge_connector_helper_funcs);
>>
>> --
>> 2.42.0
>