linux-kernel - Re: [PATCH v6 1/6] [media] vb2: add is

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Date:   Thu, 21 Dec 2017 18:32:03 -0200
From:   Gustavo Padovan <gustavo@...ovan.org>
To:     Mauro Carvalho Chehab <mchehab@....samsung.com>
Cc:     linux-media@...r.kernel.org, Hans Verkuil <hverkuil@...all.nl>,
        Shuah Khan <shuahkh@....samsung.com>,
        Pawel Osciak <pawel@...iak.com>,
        Alexandre Courbot <acourbot@...omium.org>,
        Sakari Ailus <sakari.ailus@....fi>,
        Brian Starkey <brian.starkey@....com>,
        Thierry Escande <thierry.escande@...labora.com>,
        linux-kernel@...r.kernel.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>
Subject: Re: [PATCH v6 1/6] [media] vb2: add is_unordered callback for drivers

2017-12-21 Mauro Carvalho Chehab <mchehab@....samsung.com>:

> Em Mon, 11 Dec 2017 16:27:36 -0200
> Gustavo Padovan <gustavo@...ovan.org> escreveu:
> 
> > From: Gustavo Padovan <gustavo.padovan@...labora.com>
> > 
> > Explicit synchronization benefits a lot from ordered queues, they fit
> > better in a pipeline with DRM for example so create a opt-in way for
> > drivers notify videobuf2 that the queue is unordered.
> > 
> > Drivers don't need implement it if the queue is ordered.
> > 
> > Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.com>
> > ---
> >  include/media/videobuf2-core.h | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> > index ef9b64398c8c..eddb38a2a2f3 100644
> > --- a/include/media/videobuf2-core.h
> > +++ b/include/media/videobuf2-core.h
> > @@ -368,6 +368,9 @@ struct vb2_buffer {
> >   *			callback by calling vb2_buffer_done() with either
> >   *			%VB2_BUF_STATE_DONE or %VB2_BUF_STATE_ERROR; may use
> >   *			vb2_wait_for_all_buffers() function
> > + * @is_unordered:	tell if the queue format is unordered. The default is
> > + *			assumed to be ordered and this function only needs to
> > + *			be implemented for unordered queues.
> >   * @buf_queue:		passes buffer vb to the driver; driver may start
> >   *			hardware operation on this buffer; driver should give
> >   *			the buffer back by calling vb2_buffer_done() function;
> > @@ -391,6 +394,7 @@ struct vb2_ops {
> >  
> >  	int (*start_streaming)(struct vb2_queue *q, unsigned int count);
> >  	void (*stop_streaming)(struct vb2_queue *q);
> > +	int (*is_unordered)(struct vb2_queue *q);
> >  
> >  	void (*buf_queue)(struct vb2_buffer *vb);
> >  };
> > @@ -564,6 +568,7 @@ struct vb2_queue {
> >  	u32				cnt_wait_finish;
> >  	u32				cnt_start_streaming;
> >  	u32				cnt_stop_streaming;
> > +	u32				cnt_is_unordered;
> 
> If I understand, this is just a bit, right?
> 
> if so, better to declare it as:
> 
> 	u32				cnt_is_unordered : 1;

no, is_unordered() is a vb2 callback to ask drivers if their current
queue is not ordered and cnt_is_unordered is the counter of how many
times this callback was called. This happens for all vb2 callbacks, see
the other counters above, so I decided to add one for is_unordered() as
well.

Gustavo