Subject: Re: [PATCH v2 1/3] media: cedrus: Fix decoding for some H264 videos

From: Jernej Škrabec <[email-masked]>
Date: Tue, 15 Oct 2019 19:16:32 +0200

Hi!

Sorry for late reponse, technical issues...

Dne sreda, 02. oktober 2019 ob 23:54:47 CEST je Paul Kocialkowski napisal(a):
> Hi,
> 
> On Wed 02 Oct 19, 21:35, 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.
> 
> I understand there might be some magic going on under the hood here, but I
> would be interested in trying to understand what's really going on.

Me too.

> 
> For instance, comparing register dumps of the whole H264 block before/after
> calling the hardware parser could help, and comparing that to using the
> previous code (without hardware parsing).

Please understand that I was working on this on and off for almost half a year 
and checked many times all register values. At one point I tried libvdpau-
sunxi which has no problem with sample video.  Still, all relevant register 
values were the same. In a desperate attempt, I tried with HW header parsing 
which magically solved the issue. After that, I reused values provided in 
controls and then finally I made minimal solution as suggested in this patch. 

> 
> I could try and have a look if you have an available sample for testing the
> erroneous case!

Of course: http://jernej.libreelec.tv/videos/h264/test.mkv

> 
> Another minor thing: do you have some idea of whether the udelay call adds
> significant delay in the process?

I didn't notice any issue with it. Do you have any better idea? I just didn't 
want to make empty loop and udelay is the shortest delay that is provided by 
the kernel API.

Best regards,
Jernej

> 
> Cheers and thanks for the patch!
> 
> Paul
> 
> > Signed-off-by: Jernej Skrabec <[email-masked]>
> > ---
> > 
> >  .../staging/media/sunxi/cedrus/cedrus_h264.c  | 30 +++++++++++++++++--
> >  .../staging/media/sunxi/cedrus/cedrus_regs.h  |  3 ++
> >  2 files changed, 30 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> > b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c index
> > d6a782703c9b..bd848146eada 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 +290,28 @@ static void cedrus_write_pred_weight_table(struct
> > cedrus_ctx *ctx,> 
> >  	}
> >  
> >  }
> > 
> > +/*
> > + * It turns out that using VE_H264_VLD_OFFSET to skip bits is not
> > reliable. In + * rare cases frame is not decoded correctly. However,
> > setting offset to 0 and + * skipping appropriate amount of bits with
> > flush bits trigger always works. + */
> > +static void cedrus_skip_bits(struct cedrus_dev *dev, int num)
> > +{
> > +	int count = 0;
> > +
> > +	while (count < num) {
> > +		int tmp = min(num - count, 32);
> > 
> > +
> > +		cedrus_write(dev, VE_H264_TRIGGER_TYPE,
> > +			     VE_H264_TRIGGER_TYPE_FLUSH_BITS |
> > +			     VE_H264_TRIGGER_TYPE_N_BITS(tmp));
> > +		while (cedrus_read(dev, VE_H264_STATUS) & 
VE_H264_STATUS_VLD_BUSY)
> > +			udelay(1);
> > +
> > +		count += tmp;
> > +	}
> > +}
> > +
> > 
> >  static void cedrus_set_params(struct cedrus_ctx *ctx,
> >  
> >  			      struct cedrus_run *run)
> >  
> >  {
> > 
> > @@ -299,12 +322,11 @@ static void cedrus_set_params(struct cedrus_ctx
> > *ctx,
> > 
> >  	struct vb2_buffer *src_buf = &run->src->vb2_buf;
> >  	struct cedrus_dev *dev = ctx->dev;
> >  	dma_addr_t src_buf_addr;
> > 
> > -	u32 offset = slice->header_bit_size;
> > -	u32 len = (slice->size * 8) - offset;
> > +	u32 len = slice->size * 8;
> > 
> >  	u32 reg;
> >  	
> >  	cedrus_write(dev, VE_H264_VLD_LEN, len);
> > 
> > -	cedrus_write(dev, VE_H264_VLD_OFFSET, offset);
> > +	cedrus_write(dev, VE_H264_VLD_OFFSET, 0);
> > 
> >  	src_buf_addr = vb2_dma_contig_plane_dma_addr(src_buf, 0);
> >  	cedrus_write(dev, VE_H264_VLD_END,
> > 
> > @@ -323,6 +345,8 @@ static void cedrus_set_params(struct cedrus_ctx *ctx,
> > 
> >  	cedrus_write(dev, VE_H264_TRIGGER_TYPE,
> >  	
> >  		     VE_H264_TRIGGER_TYPE_INIT_SWDEC);
> > 
> > +	cedrus_skip_bits(dev, slice->header_bit_size);
> > +
> > 
> >  	if (((pps->flags & V4L2_H264_PPS_FLAG_WEIGHTED_PRED) &&
> >  	
> >  	     (slice->slice_type == V4L2_H264_SLICE_TYPE_P ||
> >  	     
> >  	      slice->slice_type == V4L2_H264_SLICE_TYPE_SP)) ||
> > 
> > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_regs.h
> > b/drivers/staging/media/sunxi/cedrus/cedrus_regs.h index
> > 3329f9aaf975..b52926a54025 100644
> > --- a/drivers/staging/media/sunxi/cedrus/cedrus_regs.h
> > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_regs.h
> > @@ -538,13 +538,16 @@
> > 
> >  					 
VE_H264_CTRL_SLICE_DECODE_INT)
> >  
> >  #define VE_H264_TRIGGER_TYPE		0x224
> > 
> > +#define VE_H264_TRIGGER_TYPE_N_BITS(x)		(((x) & 0x3f) << 8)
> > 
> >  #define VE_H264_TRIGGER_TYPE_AVC_SLICE_DECODE	(8 << 0)
> >  #define VE_H264_TRIGGER_TYPE_INIT_SWDEC		(7 << 0)
> > 
> > +#define VE_H264_TRIGGER_TYPE_FLUSH_BITS		(3 << 0)
> > 
> >  #define VE_H264_STATUS			0x228
> >  #define VE_H264_STATUS_VLD_DATA_REQ_INT		
VE_H264_CTRL_VLD_DATA_REQ_INT
> >  #define VE_H264_STATUS_DECODE_ERR_INT		
VE_H264_CTRL_DECODE_ERR_INT
> >  #define VE_H264_STATUS_SLICE_DECODE_INT		
VE_H264_CTRL_SLICE_DECODE_INT
> > 
> > +#define VE_H264_STATUS_VLD_BUSY			BIT(8)
> > 
> >  #define VE_H264_STATUS_INT_MASK			
VE_H264_CTRL_INT_MASK

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