linux-kernel - Re: [PATCHv4 01/11] videobuf2: add cache management members

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Message-ID: <20200309034411.GA856@jagdpanzerIV.localdomain>
Date:   Mon, 9 Mar 2020 12:44:11 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     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>,
        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 <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCHv4 01/11] videobuf2: add cache management members

On (20/03/09 12:27), Sergey Senozhatsky wrote:
> On (20/03/07 12:47), Hans Verkuil wrote:
> > 
> > Create those tests in v4l2-compliance: that's where they belong.
> >
> > You need these tests:
> > 
> > For non-MMAP modes:
> > 
> > 1) test that V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS is never set.
> > 
> > If V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS is not set, then:
> > 
> > 1) attempting to use V4L2_FLAG_MEMORY_NON_CONSISTENT will clear the flag
> >    upon return (test with both reqbufs and create_bufs).
> > 2) attempting to use V4L2_BUF_FLAG_NO_CACHE_INVALIDATE or V4L2_BUF_FLAG_NO_CACHE_CLEAN
> >    will clear those flags upon return (do we actually do that in the patch series?).
> 
> NO_CACHE_INVALIDATE/NO_CACHE_CLEAN are cleared in vb2_fill_vb2_v4l2_buffer()
> [as was suggested], then the struct is copied back to user. But I think it
> would be better to clear those flags when we clear
> V4L2_FLAG_MEMORY_NON_CONSISTENT. We have 4 places which do something
> like
> 	"if !vb2_queue_allows_cache_hints(q) then clear flags bit".

No. I'll just move NO_CACHE_INVALIDATE/NO_CACHE_CLEAN handling to
set_buffer_cache_hints(). This is where we take care of q->memory
and q->allow_cache_hints, this is where we set/clear the
->need_cache_sync flags, this is where we also can clear v4l2_buffer
->flags. Seems like a better place than vb2_fill_vb2_v4l2_buffer().

---
 .../media/common/videobuf2/videobuf2-v4l2.c   | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
index b4b379f3bf98..0a6bd4a1f58e 100644
--- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
+++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
@@ -199,15 +199,6 @@ static int vb2_fill_vb2_v4l2_buffer(struct vb2_buffer *vb, struct v4l2_buffer *b
 	vbuf->request_fd = -1;
 	vbuf->is_held = false;
 
-	/*
-	 * Clear buffer cache flags if queue does not support user space hints.
-	 * That's to indicate to userspace that these flags won't work.
-	 */
-	if (!vb2_queue_allows_cache_hints(q)) {
-		b->flags &= ~V4L2_BUF_FLAG_NO_CACHE_INVALIDATE;
-		b->flags &= ~V4L2_BUF_FLAG_NO_CACHE_CLEAN;
-	}
-
 	if (V4L2_TYPE_IS_MULTIPLANAR(b->type)) {
 		switch (b->memory) {
 		case VB2_MEMORY_USERPTR:
@@ -368,8 +359,16 @@ static void set_buffer_cache_hints(struct vb2_queue *q,
 	vb->need_cache_sync_on_prepare = 1;
 	vb->need_cache_sync_on_finish = 1;
 
-	if (!vb2_queue_allows_cache_hints(q))
+	if (!vb2_queue_allows_cache_hints(q)) {
+		/*
+		 * Clear buffer cache flags if queue does not support user
+		 * space hints. That's to indicate to userspace that these
+		 * flags won't work.
+		 */
+		b->flags &= ~V4L2_BUF_FLAG_NO_CACHE_INVALIDATE;
+		b->flags &= ~V4L2_BUF_FLAG_NO_CACHE_CLEAN;
 		return;
+	}
 
 	/*
 	 * ->finish() cache sync can be avoided when queue direction is
-- 
2.25.1