linux-kernel - Re: [PATCH] media: imx: prpencvf: enable double write reduction

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Date:   Sat, 22 Jul 2017 15:04:57 -0700
From:   Steve Longerbeam <slongerbeam@...il.com>
To:     Philipp Zabel <p.zabel@...gutronix.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-media@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: imx: prpencvf: enable double write reduction

Hi Philipp,

This is the same as your patch to CSI, applied to ic-prpencvf.

I'm not really sure what this cpmem bit is doing. The U/V planes
in memory are already subsampled by 2 in both width and height.
This must be referring to what the IDMAC is transferring on the bus,
but why would it place duplicate U/V samples on the bus in the first
place?

Anyway, thanks for the heads-up on this.

Steve


On 07/22/2017 02:21 PM, Steve Longerbeam wrote:
> For the write channels with 4:2:0 subsampled YUV formats, avoid chroma
> overdraw by only writing chroma for even lines. Reduces necessary write
> memory bandwidth by at least 25% (more with rotation enabled).
>
> Signed-off-by: Steve Longerbeam<steve_longerbeam@...tor.com>
> ---
>   drivers/staging/media/imx/imx-ic-prpencvf.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
>
> diff --git a/drivers/staging/media/imx/imx-ic-prpencvf.c b/drivers/staging/media/imx/imx-ic-prpencvf.c
> index ed363fe..42c5045 100644
> --- a/drivers/staging/media/imx/imx-ic-prpencvf.c
> +++ b/drivers/staging/media/imx/imx-ic-prpencvf.c
> @@ -374,6 +374,17 @@ static int prp_setup_channel(struct prp_priv *priv,
>   	image.phys0 = addr0;
>   	image.phys1 = addr1;
>   
> +	if (channel == priv->out_ch || channel == priv->rot_out_ch) {
> +		switch (image.pix.pixelformat) {
> +		case V4L2_PIX_FMT_YUV420:
> +		case V4L2_PIX_FMT_YVU420:
> +		case V4L2_PIX_FMT_NV12:
> +			/* Skip writing U and V components to odd rows */
> +			ipu_cpmem_skip_odd_chroma_rows(channel);
> +			break;
> +		}
> +	}
> +
>   	ret = ipu_cpmem_set_image(channel, &image);
>   	if (ret)
>   		return ret;