videobuf & read/write operation

videobuf & read/write operation

[Ran Shalit]

Hello,

I'm trying to understand how to imeplement v4l driver using videobuf.
The videobuf documentation if very helpful.
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

Re: videobuf & read/write operation

[Hans Verkuil]

On 11/01/2015 08:21 PM, Ran Shalit wrote:
> Hello,
> 
> I'm trying to understand how to imeplement v4l driver using videobuf.
> The videobuf documentation if very helpful.

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?

Regards,

	Hans

> 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
> --
> To unsubscribe from this list: send the line "unsubscribe linux-media" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: videobuf & read/write operation

[Ran Shalit]

> 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 ?


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
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-media" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>

Re: videobuf & read/write operation

[Hans Verkuil]

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
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-media" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>>