Re: videobuf & read/write operation

[Hans Verkuil <hverkuil@xs4all.nl>]

On 11/01/2015 09:13 PM, Ran Shalit wrote:
>> Don't use videobuf! Use videobuf2, just like the skeleton driver.
>>
>> The old videobuf framework is deprecated and you shouldn't use it as it is
>> horrible.
>>
>> Why on earth are you trying to use videobuf if the skeleton driver clearly
>> uses vb2?
>>
> 
> Right,
> I now see that I was examining code which is quite old (2.6.37 from
> SDK I'm using).
> 
> In case we only need read/write operation, do we still need to
> implement all videobuf2 APIs ?

vb2 only got merged in 2.6.39. For what kernel are you doing this? 2.6.37 is ancient.

Anyway, for read/write you implement exactly the same vb2 callbacks as for stream I/O.
Read/write is implemented in the vb2 framework on top of stream I/O.

Typically drivers will have to implement queue_setup, buf_queue and start/stop_streaming
at minimum. The wait_prepare/finish callbacks are also needed, but you can typically use
the vb2_ops_wait_prepare/finish helper functions for that. Again, follow what the skeleton
driver does.

Regards,

	Hans

> 
> 
> Regards,
> Ran
> 
> 
>>
>>> When the documentation refers to " I/O stream" , does it also include
>>> the read/write operation or only streaming I/O method ?
>>>
>>> In case I am using only read/write, do I need to implement all these 4  APIs:
>>>
>>> struct videobuf_queue_ops {
>>>  int (*buf_setup)(struct videobuf_queue *q,
>>>  unsigned int *count, unsigned int *size);
>>>  int (*buf_prepare)(struct videobuf_queue *q,
>>>  struct videobuf_buffer *vb,
>>> enum v4l2_field field);
>>>  void (*buf_queue)(struct videobuf_queue *q,
>>>  struct videobuf_buffer *vb);
>>>  void (*buf_release)(struct videobuf_queue *q,
>>>  struct videobuf_buffer *vb);
>>> };
>>>
>>> Are these APIs relevant for both read/write and streaminf I/O ?
>>>
>>> Best Regards,
>>> Ran
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>>