linux-kernel - [PATCH v2 2/2] media: rkisp1: Allow non-coherent video capture buffers

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Message-Id: <20250115-b4-rkisp-noncoherent-v2-2-0853e1a24012@gmail.com>
Date: Wed, 15 Jan 2025 20:25:06 +0300
From: Mikhail Rudenko <mike.rudenko@...il.com>
To: Dafna Hirschfeld <dafna@...tmail.com>, 
 Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
 Mauro Carvalho Chehab <mchehab@...nel.org>, 
 Heiko Stuebner <heiko@...ech.de>, Tomasz Figa <tfiga@...omium.org>, 
 Marek Szyprowski <m.szyprowski@...sung.com>, 
 Hans Verkuil <hverkuil@...all.nl>, 
 Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: linux-media@...r.kernel.org, linux-rockchip@...ts.infradead.org, 
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Mauro Carvalho Chehab <mchehab+huawei@...nel.org>, 
 Mikhail Rudenko <mike.rudenko@...il.com>
Subject: [PATCH v2 2/2] media: rkisp1: Allow non-coherent video capture
 buffers

Currently, the rkisp1 driver always uses coherent DMA allocations for
video capture buffers. However, on some platforms, using non-coherent
buffers can improve performance, especially when CPU processing of
MMAP'ed video buffers is required.

For example, on the Rockchip RK3399 running at maximum CPU frequency,
the time to memcpy a frame from a 1280x720 XRGB32 MMAP'ed buffer to a
malloc'ed userspace buffer decreases from 7.7 ms to 1.1 ms when using
non-coherent DMA allocation. When doing cache management with
DMA_BUF_IOCTL_SYNC, DMA_BUF_SYNC_START and DMA_BUF_SYNC_END operations
take around 270 us each.

This change allows userspace to request the allocation of non-coherent
buffers. Note that the behavior for existing users will remain unchanged
unless they explicitly set the V4L2_MEMORY_FLAG_NON_COHERENT flag when
allocating buffers.

Signed-off-by: Mikhail Rudenko <mike.rudenko@...il.com>
---
 drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c b/drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c
index 6dcefd144d5abe358323e37ac6133c6134ac636e..c94f7d1d73a92646457a27da20726ec6f92e7717 100644
--- a/drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c
+++ b/drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c
@@ -1563,6 +1563,7 @@ static int rkisp1_register_capture(struct rkisp1_capture *cap)
 	q->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
 	q->lock = &node->vlock;
 	q->dev = cap->rkisp1->dev;
+	q->allow_cache_hints = 1;
 	ret = vb2_queue_init(q);
 	if (ret) {
 		dev_err(cap->rkisp1->dev,

-- 
2.47.1