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

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Date:	Fri, 4 Oct 2013 16:16:38 +0200
From:	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
To:	Hans Verkuil <hverkuil@...all.nl>
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 <linux-media@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vb2: Allow STREAMOFF for io emulator

Hello Hans

I am implementing a test application for our camera, think of
v4l2-compliance but for testing the hardware (average of pixels,
rotation...) . I am implementing it using python (because of numpy and
matplotlib).

I dont really care about perferomance, I only care about the data
correctness, so the fileio fits perfectly my needs.

On the fileio api we dont have a way to tell the camera to stop, this
was an attempt to solve this "issue". But if it is only an issue for
me we can forget about it :).

BTW, do you know about a complete v4l2 library for python? I am using
https://pypi.python.org/pypi/v4l2 , but it is quite old.

Thanks!


On Fri, Oct 4, 2013 at 4:09 PM, Hans Verkuil <hverkuil@...all.nl> wrote:
> 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.
>>
>



-- 
Ricardo Ribalda
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