linux-kernel - Re: [PATCH] media: ti: j721e-csi2rx: Allow passing cache hints from user-space

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Message-ID: <aFxjWFFLekPp54a2@valkosipuli.retiisi.eu>
Date: Wed, 25 Jun 2025 21:00:08 +0000
From: Sakari Ailus <sakari.ailus@....fi>
To: Devarsh Thakkar <devarsht@...com>
Cc: jai.luthra@...ux.dev, mchehab@...nel.org, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, s-jain1@...com, r-donadkar@...com,
	vigneshr@...com, praneeth@...com, tomi.valkeinen@...asonboard.com,
	y-abhilashchandra@...com
Subject: Re: [PATCH] media: ti: j721e-csi2rx: Allow passing cache hints from
 user-space

Hi Devarsh,

Thanks for the patch.

On Wed, Mar 12, 2025 at 04:51:40PM +0530, Devarsh Thakkar wrote:
> User-space can provide cache hints to enable software managed cache
> operations or skip certain cache operations using memory flags
> and buffer flags. This is useful for SoCs such as AM62px
> which do not support hardware cache coherency.
> 
> This is tested on AM62px with yavta capture by passing
> V4L2_MEMORY_FLAG_NON_COHERENT while using VIDIOC_REQBUFS
> and V4L2_BUF_FLAG_NO_CACHE_CLEAN while using VIDIOC_QBUF
> and ~5x reduction in memcpy time is seen for
> copying captured frame to DDR as shared here [1].

The lines may be up to 75 characters long here. Most editors can handle the
wrapping for you, I've rewrapped the text in this case and edited it a
little, as Jai suggested.

> 
> [1]:
> Link: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1452545/am62p-the-ads6311-radar-camera-has-lost-frame-capture/5580472#5580472
> Signed-off-by: Devarsh Thakkar <devarsht@...com>
> ---
>  drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c b/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
> index 6412a00be8ea..284d33b2a0ec 100644
> --- a/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
> +++ b/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
> @@ -895,6 +895,7 @@ static int ti_csi2rx_init_vb2q(struct ti_csi2rx_dev *csi)
>  	q->dev = dmaengine_get_dma_device(csi->dma.chan);
>  	q->lock = &csi->mutex;
>  	q->min_queued_buffers = 1;
> +	q->allow_cache_hints = 1;
>  
>  	ret = vb2_queue_init(q);
>  	if (ret)

-- 
Regards,

Sakari Ailus