linux-kernel - Re: [PATCH v2 05/10] media: hantro: Reduce H264 extra space for motion vectors

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Date:   Thu, 31 Oct 2019 10:50:25 +0100
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Jonas Karlman <jonas@...boo.se>
Cc:     Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Hans Verkuil <hverkuil@...all.nl>,
        Tomasz Figa <tfiga@...omium.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 05/10] media: hantro: Reduce H264 extra space for
 motion vectors

On Tue, 29 Oct 2019 01:24:50 +0000
Jonas Karlman <jonas@...boo.se> wrote:

> A decoded 8-bit 4:2:0 frame need memory for up to 448 bytes per
> macroblock with additional 32 bytes on multi-core variants.
> 
> Memory layout is as follow:
> 
> +---------------------------+
> | Y-plane   256 bytes x MBs |
> +---------------------------+
> | UV-plane  128 bytes x MBs |
> +---------------------------+
> | MV buffer  64 bytes x MBs |
> +---------------------------+
> | MC sync          32 bytes |
> +---------------------------+

As for patch 4, can we point this diagram as a comment in the code too?

> 
> Reduce the extra space allocated now that motion vector buffer offset no
> longer is based on the extra space.
> 
> Only allocate extra space for 64 bytes x MBs of motion vector buffer
> and 32 bytes for multi-core sync.
> 
> Fixes: a9471e25629b ("media: hantro: Add core bits to support H264 decoding")
> Signed-off-by: Jonas Karlman <jonas@...boo.se>

Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>

> ---
> Changes in v2:
>   - updated commit message
> ---
>  drivers/staging/media/hantro/hantro_v4l2.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/media/hantro/hantro_v4l2.c b/drivers/staging/media/hantro/hantro_v4l2.c
> index 3dae52abb96c..b3a4368b37de 100644
> --- a/drivers/staging/media/hantro/hantro_v4l2.c
> +++ b/drivers/staging/media/hantro/hantro_v4l2.c
> @@ -242,12 +242,12 @@ static int vidioc_try_fmt(struct file *file, void *priv, struct v4l2_format *f,
>  		/*
>  		 * The H264 decoder needs extra space on the output buffers
>  		 * to store motion vectors. This is needed for reference
> -		 * frames.
> +		 * frames. 32 extra bytes is used for multi-core sync.
>  		 */
>  		if (ctx->vpu_src_fmt->fourcc == V4L2_PIX_FMT_H264_SLICE)
>  			pix_mp->plane_fmt[0].sizeimage +=
> -				128 * DIV_ROUND_UP(pix_mp->width, 16) *
> -				      DIV_ROUND_UP(pix_mp->height, 16);
> +				64 * MB_WIDTH(pix_mp->width) *
> +				     MB_WIDTH(pix_mp->height) + 32;
>  	} else if (!pix_mp->plane_fmt[0].sizeimage) {
>  		/*
>  		 * For coded formats the application can specify