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Message-ID: <X8ENifLanjYuhF/r@jagdpanzerIV.localdomain>
Date: Fri, 27 Nov 2020 23:30:33 +0900
From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To: Hans Verkuil <hverkuil@...all.nl>
Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Tomasz Figa <tfiga@...omium.org>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH] media: vb2: always set buffer cache sync hints
On (20/11/27 13:59), Hans Verkuil wrote:
>
> I think this needs a comment, basically explaining what you said in
> the commit log. It's not obvious from the code that this is a
> workaround.
Something like this?
---
diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index 5499013cf82e..21b2b0ae3629 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -414,6 +414,16 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
vb->index = q->num_buffers + buffer;
vb->type = q->type;
vb->memory = memory;
+ /*
+ * A workaround fix. We need to set these flags here so that
+ * videobuf2 core will always call ->prepare()/->finish()
+ * cache sync/flush on vb2 buffers. Otherwise, for backends
+ * that don't rely on V4L2 (perhaps dvb) these flags will
+ * always be false and, hence, videobuf2 core will skip cache
+ * sync/flush operations.
+ */
+ vb->need_cache_sync_on_prepare = 1;
+ vb->need_cache_sync_on_finish = 1;
for (plane = 0; plane < num_planes; ++plane) {
vb->planes[plane].length = plane_sizes[plane];
vb->planes[plane].min_length = plane_sizes[plane];
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