linux-kernel - Re: [PATCH 3/7] media: cedrus: Fix decoding for some H264 videos

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Date:   Mon, 3 Jun 2019 13:55:36 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Jernej Skrabec <jernej.skrabec@...l.net>
Cc:     paul.kocialkowski@...tlin.com, wens@...e.org, mchehab@...nel.org,
        gregkh@...uxfoundation.org, linux-media@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] media: cedrus: Fix decoding for some H264 videos

Hi,

On Thu, May 30, 2019 at 11:15:12PM +0200, Jernej Skrabec wrote:
> It seems that for some H264 videos at least one bitstream parsing
> trigger must be called in order to be decoded correctly. There is no
> explanation why this helps, but it was observed that two sample videos
> with this fix are now decoded correctly and there is no regression with
> others.
>
> Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> ---
> I have two samples which are fixed by this:
> http://jernej.libreelec.tv/videos/h264/test.mkv
> http://jernej.libreelec.tv/videos/h264/Dredd%20%E2%80%93%20DTS%20Sound%20Check%20DTS-HD%20MA%207.1.m2ts
>
> Although second one also needs support for multi-slice frames, which is not yet implemented here.
>
>  .../staging/media/sunxi/cedrus/cedrus_h264.c  | 22 ++++++++++++++++---
>  1 file changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> index cc8d17f211a1..d0ee3f90ff46 100644
> --- a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> +++ b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> @@ -6,6 +6,7 @@
>   * Copyright (c) 2018 Bootlin
>   */
>
> +#include <linux/delay.h>
>  #include <linux/types.h>
>
>  #include <media/videobuf2-dma-contig.h>
> @@ -289,6 +290,20 @@ static void cedrus_write_pred_weight_table(struct cedrus_ctx *ctx,
>  	}
>  }

We should have a comment here explaining why that is needed

> +static void cedrus_skip_bits(struct cedrus_dev *dev, int num)
> +{
> +	for (; num > 32; num -= 32) {
> +		cedrus_write(dev, VE_H264_TRIGGER_TYPE, 0x3 | (32 << 8));

Using defines here would be great

> +		while (cedrus_read(dev, VE_H264_STATUS) & (1 << 8))
> +			udelay(1);
> +	}

A new line here would be great

> +	if (num > 0) {
> +		cedrus_write(dev, VE_H264_TRIGGER_TYPE, 0x3 | (num << 8));
> +		while (cedrus_read(dev, VE_H264_STATUS) & (1 << 8))
> +			udelay(1);
> +	}

Can't we make that a bit simpler by not duplicating the loop?

Something like:

int current = 0;

while (current < num) {
    int tmp = min(num - current, 32);

    cedrus_write(dev, VE_H264_TRIGGER_TYPE, 0x3 | (current << 8))
    while (...)
       ...

    current += tmp;
}

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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