linux-kernel - Re: [PATCH] vb2: Allow STREAMOFF for io emulator

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Date:	Fri, 04 Oct 2013 16:09:10 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
CC:	Pawel Osciak <pawel@...iak.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vb2: Allow STREAMOFF for io emulator

Hi Ricardo,

On 10/04/2013 03:49 PM, Ricardo Ribalda Delgado wrote:
> A video device opened and streaming in io emulator mode can only stop
> streamming if its file descriptor is closed.
> 
> There are some parameters that can only be changed if the device is not
> streaming. Also, the power consumption of a device streaming could be
> different than one not streaming.
> 
> With this patch a video device opened in io emulator can be stopped on
> demand.

Why would you want this? If you can call STREAMOFF, why not use stream I/O
all the way? That's much more efficient than read() anyway.

Unless there is a very good use-case, I don't see a good reason for mixing
file I/O with streaming I/O ioctls.

Regards,

	Hans

> 
> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
> ---
>  drivers/media/v4l2-core/videobuf2-core.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index 9fc4bab..097fba8 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -1686,6 +1686,7 @@ int vb2_streamon(struct vb2_queue *q, enum v4l2_buf_type type)
>  }
>  EXPORT_SYMBOL_GPL(vb2_streamon);
>  
> +static int __vb2_cleanup_fileio(struct vb2_queue *q);
>  
>  /**
>   * vb2_streamoff - stop streaming
> @@ -1704,11 +1705,6 @@ EXPORT_SYMBOL_GPL(vb2_streamon);
>   */
>  int vb2_streamoff(struct vb2_queue *q, enum v4l2_buf_type type)
>  {
> -	if (q->fileio) {
> -		dprintk(1, "streamoff: file io in progress\n");
> -		return -EBUSY;
> -	}
> -
>  	if (type != q->type) {
>  		dprintk(1, "streamoff: invalid stream type\n");
>  		return -EINVAL;
> @@ -1719,6 +1715,11 @@ int vb2_streamoff(struct vb2_queue *q, enum v4l2_buf_type type)
>  		return -EINVAL;
>  	}
>  
> +	if (q->fileio) {
> +		__vb2_cleanup_fileio(q);
> +		return 0;
> +	}
> +
>  	/*
>  	 * Cancel will pause streaming and remove all buffers from the driver
>  	 * and videobuf, effectively returning control over them to userspace.
> 

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