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SubjectRe: [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@siol.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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