linux-kernel - [RFC v5 03/11] [media] vb2: add 'ordered_in

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Date:   Wed, 15 Nov 2017 15:10:49 -0200
From:   Gustavo Padovan <gustavo@...ovan.org>
To:     linux-media@...r.kernel.org
Cc:     Hans Verkuil <hverkuil@...all.nl>,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        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: [RFC v5 03/11] [media] vb2: add 'ordered_in_driver' property to queues

From: Gustavo Padovan <gustavo.padovan@...labora.com>

We use ordered_in_driver property to optimize for the case where
the driver can deliver the buffers in an ordered fashion. When it
is ordered we can use the same fence context for all fences, but
when it is not we need to a new context for each out-fence.

So the ordered_in_driver flag will help us with identifying the queues
that can be optimized and use the same fence context.

v4: make the property a vector for optimization and not a mandatory thing
that drivers need to set if they want to use explicit synchronization.

v3: improve doc (Hans Verkuil)

v2: rename property to 'ordered_in_driver' to avoid confusion

Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.com>
---
 include/media/videobuf2-core.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index ef9b64398c8c..38b9c8dd42c6 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -440,6 +440,12 @@ struct vb2_buf_ops {
  * @fileio_read_once:		report EOF after reading the first buffer
  * @fileio_write_immediately:	queue buffer after each write() call
  * @allow_zero_bytesused:	allow bytesused == 0 to be passed to the driver
+ * @ordered_in_driver: if the driver can guarantee that the queue will be
+ *		ordered or not, i.e., the buffers are dequeued from the driver
+ *		in the same order they are queued to the driver. The default
+ *		is not ordered unless the driver sets this flag. Setting it
+ *		when ordering can be guaranted helps to optimize explicit
+ *		fences.
  * @quirk_poll_must_check_waiting_for_buffers: Return POLLERR at poll when QBUF
  *              has not been called. This is a vb1 idiom that has been adopted
  *              also by vb2.
@@ -510,6 +516,7 @@ struct vb2_queue {
 	unsigned			fileio_read_once:1;
 	unsigned			fileio_write_immediately:1;
 	unsigned			allow_zero_bytesused:1;
+	unsigned			ordered_in_driver:1;
 	unsigned		   quirk_poll_must_check_waiting_for_buffers:1;
 
 	struct mutex			*lock;
-- 
2.13.6