linux-kernel - Re: [PATCH 1/2] media: stm32-dcmi: create video dev within notifier bound

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Message-ID: <31ca9ccc-77d4-4368-1024-db70e8e1e7f2@xs4all.nl>
Date:   Wed, 19 Aug 2020 15:52:40 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Alain Volmat <alain.volmat@...com>, hugues.fruchet@...com,
        mchehab@...nel.org
Cc:     mcoquelin.stm32@...il.com, alexandre.torgue@...com,
        yannick.fertre@...com, hans.verkuil@...co.com,
        linux-media@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] media: stm32-dcmi: create video dev within notifier
 bound

On 28/07/2020 08:37, Alain Volmat wrote:
> In case of an error during the initialization of the sensor,
> the video device is still available since created at the
> probe of the dcmi driver. Moreover the device wouldn't
> be released even when removing the module since the release
> is performed as part of the notifier unbind callback
> (not called if no sensor is properly initialized).
> 
> This patch move the video device creation with the v4l2 notifier
> bound handler in order to avoid having a video device created when
> an error happen during the pipe (dcmi - sensor) initialization.
> 
> This also makes the video device creation symmetric with the
> release which is already done within the notifier unbind handler.
> 
> Fixes: 37404f91ef8b ("[media] stm32-dcmi: STM32 DCMI camera interface driver")
> Signed-off-by: Alain Volmat <alain.volmat@...com>
> ---
>  drivers/media/platform/stm32/stm32-dcmi.c | 23 ++++++++++++-----------
>  1 file changed, 12 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/media/platform/stm32/stm32-dcmi.c b/drivers/media/platform/stm32/stm32-dcmi.c
> index b8931490b83b..5e60d4c6eeeb 100644
> --- a/drivers/media/platform/stm32/stm32-dcmi.c
> +++ b/drivers/media/platform/stm32/stm32-dcmi.c
> @@ -1747,6 +1747,15 @@ static int dcmi_graph_notify_bound(struct v4l2_async_notifier *notifier,
>  
>  	dev_dbg(dcmi->dev, "Subdev \"%s\" bound\n", subdev->name);
>  
> +	ret = video_register_device(dcmi->vdev, VFL_TYPE_VIDEO, -1);
> +	if (ret) {
> +		dev_err(dcmi->dev, "Failed to register video device\n");
> +		return ret;
> +	}

Why in the bound callback? The video device is typically created in the complete
callback, since that's the point where everything is ready.

You should not create a video device unless it is ready for use, and that's only
valid at the end of the complete callback.

Regards,

	Hans

> +
> +	dev_dbg(dcmi->dev, "Device registered as %s\n",
> +		video_device_node_name(dcmi->vdev));
> +
>  	/*
>  	 * Link this sub-device to DCMI, it could be
>  	 * a parallel camera sensor or a bridge
> @@ -1759,10 +1768,11 @@ static int dcmi_graph_notify_bound(struct v4l2_async_notifier *notifier,
>  				    &dcmi->vdev->entity, 0,
>  				    MEDIA_LNK_FL_IMMUTABLE |
>  				    MEDIA_LNK_FL_ENABLED);
> -	if (ret)
> +	if (ret) {
>  		dev_err(dcmi->dev, "Failed to create media pad link with subdev \"%s\"\n",
>  			subdev->name);
> -	else
> +		video_unregister_device(dcmi->vdev);
> +	} else
>  		dev_dbg(dcmi->dev, "DCMI is now linked to \"%s\"\n",
>  			subdev->name);
>  
> @@ -1974,15 +1984,6 @@ static int dcmi_probe(struct platform_device *pdev)
>  	}
>  	dcmi->vdev->entity.flags |= MEDIA_ENT_FL_DEFAULT;
>  
> -	ret = video_register_device(dcmi->vdev, VFL_TYPE_VIDEO, -1);
> -	if (ret) {
> -		dev_err(dcmi->dev, "Failed to register video device\n");
> -		goto err_media_entity_cleanup;
> -	}
> -
> -	dev_dbg(dcmi->dev, "Device registered as %s\n",
> -		video_device_node_name(dcmi->vdev));
> -
>  	/* Buffer queue */
>  	q->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
>  	q->io_modes = VB2_MMAP | VB2_READ | VB2_DMABUF;
>