linux-kernel - [RFC][PATCHv2 01/12] videobuf2: add cache management members

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Message-Id: <20200204025641.218376-2-senozhatsky@chromium.org>
Date:   Tue,  4 Feb 2020 11:56:30 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Hans Verkuil <hans.verkuil@...co.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Sakari Ailus <sakari.ailus@....fi>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Pawel Osciak <posciak@...omium.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [RFC][PATCHv2 01/12] videobuf2: add cache management members

Extend vb2_buffer and vb2_queue structs with cache management
members.

V4L2 UAPI already contains two buffer flags which user-space,
supposedly, can use to control buffer cache sync:

- V4L2_BUF_FLAG_NO_CACHE_INVALIDATE
- V4L2_BUF_FLAG_NO_CACHE_CLEAN

None of these, however, do anything at the moment. This patch
set is intended to change it.

Since user-space cache management hints are supposed to be
implemented on a per-buffer basis we need to extend vb2_buffer
struct with two new memebers ->need_cache_sync_on_prepare and
->need_cache_sync_on_finish, which will store corresponding
user-space hints.

In order to preserve the existing behaviour, user-space cache
managements flags will be handled only by those drivers that
permit user-space cache hints. That's the purpose of vb2_queue
->allow_cache_hints member. Driver must set ->allow_cache_hints
during queue initialisation to enable cache management hints
mechanism.

Only drivers that set ->allow_cache_hints during queue initialisation
will handle user-space cache management hints. Otherwise hints
will be ignored.

Change-Id: I52beec2a0d021b7a3715b4f6ae4bfd9dc5e94f0d
Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
---
 include/media/videobuf2-core.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index a2b2208b02da..026004180440 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -263,6 +263,10 @@ struct vb2_buffer {
 	 *			after the 'buf_finish' op is called.
 	 * copied_timestamp:	the timestamp of this capture buffer was copied
 	 *			from an output buffer.
+	 * need_cache_sync_on_prepare: do not sync/invalidate cache from
+	 * 			buffer's ->prepare() callback.
+	 * need_cache_sync_on_finish: do not sync/invalidate cache from buffer's
+	 * 			->finish() callback.
 	 * queued_entry:	entry on the queued buffers list, which holds
 	 *			all buffers queued from userspace
 	 * done_entry:		entry on the list that stores all buffers ready
@@ -273,6 +277,8 @@ struct vb2_buffer {
 	unsigned int		synced:1;
 	unsigned int		prepared:1;
 	unsigned int		copied_timestamp:1;
+	unsigned int		need_cache_sync_on_prepare:1;
+	unsigned int		need_cache_sync_on_finish:1;
 
 	struct vb2_plane	planes[VB2_MAX_PLANES];
 	struct list_head	queued_entry;
@@ -491,6 +497,9 @@ struct vb2_buf_ops {
  * @uses_requests: requests are used for this queue. Set to 1 the first time
  *		a request is queued. Set to 0 when the queue is canceled.
  *		If this is 1, then you cannot queue buffers directly.
+ * @allow_cache_hints: when set user-space can pass cache management hints in
+ * 		order to skip cache flush/invalidation on ->prepare() or/and
+ * 		->finish().
  * @lock:	pointer to a mutex that protects the &struct vb2_queue. The
  *		driver can set this to a mutex to let the v4l2 core serialize
  *		the queuing ioctls. If the driver wants to handle locking
@@ -564,6 +573,7 @@ struct vb2_queue {
 	unsigned			requires_requests:1;
 	unsigned			uses_qbuf:1;
 	unsigned			uses_requests:1;
+	unsigned			allow_cache_hints:1;
 
 	struct mutex			*lock;
 	void				*owner;
-- 
2.25.0.341.g760bfbb309-goog