linux-kernel - Re: [PATCH] media: rkisp1: allow non-coherent video capture buffers

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Message-ID: <20250103152326.GP554@pendragon.ideasonboard.com>
Date: Fri, 3 Jan 2025 17:23:26 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Mikhail Rudenko <mike.rudenko@...il.com>
Cc: Dafna Hirschfeld <dafna@...tmail.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Heiko Stuebner <heiko@...ech.de>, linux-media@...r.kernel.org,
	linux-rockchip@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: rkisp1: allow non-coherent video capture buffers

On Thu, Jan 02, 2025 at 06:35:00PM +0300, Mikhail Rudenko wrote:
> 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. CPU usage also decreases accordingly.

What's the time taken by the cache management operations ?

> 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,
> 
> ---
> base-commit: 40ed9e9b2808beeb835bd0ed971fb364c285d39c
> change-id: 20241231-b4-rkisp-noncoherent-ad6e7c7a68ba

-- 
Regards,

Laurent Pinchart