Re: [linux-sunxi] [PATCH v2 2/2] media: cedrus: Add H264 decoding support

[Maxime Ripard]

On Tue, Nov 27, 2018 at 05:30:00PM +0100, Jernej Åkrabec wrote:
> > > > +static void _cedrus_write_ref_list(struct cedrus_ctx *ctx,
> > > > +				   struct cedrus_run *run,
> > > > +				   const u8 *ref_list, u8 num_ref,
> > > > +				   enum cedrus_h264_sram_off sram)
> > > > +{
> > > > +	const struct v4l2_ctrl_h264_decode_param *decode =
> > > > run->h264.decode_param; +	struct vb2_queue *cap_q =
> > > > &ctx->fh.m2m_ctx->cap_q_ctx.q;
> > > > +	struct cedrus_dev *dev = ctx->dev;
> > > > +	u32 sram_array[CEDRUS_MAX_REF_IDX / sizeof(u32)];
> > > > +	unsigned int size, i;
> > > > +
> > > > +	memset(sram_array, 0, sizeof(sram_array));
> > > > +
> > > > +	for (i = 0; i < num_ref; i += 4) {
> > > > +		unsigned int j;
> > > > +
> > > > +		for (j = 0; j < 4; j++) {
> > > 
> > > I don't think you have to complicate with two loops here.
> > > cedrus_h264_write_sram() takes void* and it aligns to 4 anyway. So as long
> > > input buffer is multiple of 4 (u8[CEDRUS_MAX_REF_IDX] qualifies for that),
> > > you can use single for loop with "u8 sram_array[CEDRUS_MAX_REF_IDX]".
> > > This should make code much more readable.
> > 
> > This wasn't really about the alignment, but in order to get the
> > offsets in the u32 and the array more easily.
> > 
> > Breaking out the loop will make that computation less easy on the eye,
> > so I guess it's very subjective.
> > 
> 
> For some strange reason, code below fixes decoding issue from one of my test 
> samples. This is what I actually meant with 1 loop approach:

Do you have that test sample somewhere accessible?

> static void _cedrus_write_ref_list(struct cedrus_ctx *ctx,
> 				   struct cedrus_run *run,
> 				   const u8 *ref_list, u8 num_ref,
> 				   enum cedrus_h264_sram_off sram)
> {
> 	const struct v4l2_ctrl_h264_decode_param *decode = run->h264.decode_param;
> 	struct vb2_queue *cap_q = &ctx->fh.m2m_ctx->cap_q_ctx.q;
> 	struct cedrus_dev *dev = ctx->dev;
> 	u8 sram_array[CEDRUS_MAX_REF_IDX];
> 	unsigned int i;
> 
> 	memset(sram_array, 0, sizeof(sram_array));
> 	num_ref = min(num_ref, (u8)CEDRUS_MAX_REF_IDX);
> 
> 	for (i = 0; i < num_ref; i++) {
> 		const struct v4l2_h264_dpb_entry *dpb;
> 		const struct cedrus_buffer *cedrus_buf;
> 		const struct vb2_v4l2_buffer *ref_buf;
> 		unsigned int position;
> 		int buf_idx;
> 		u8 dpb_idx;
> 
> 		dpb_idx = ref_list[i];
> 		dpb = &decode->dpb[dpb_idx];
> 
> 		if (!(dpb->flags & V4L2_H264_DPB_ENTRY_FLAG_ACTIVE))
> 			continue;
> 
> 		buf_idx = vb2_find_tag(cap_q, dpb->tag, 0);
> 		if (buf_idx < 0)
> 			continue;
> 
> 		ref_buf = to_vb2_v4l2_buffer(ctx->dst_bufs[buf_idx]);
> 		cedrus_buf = vb2_v4l2_to_cedrus_buffer(ref_buf);
> 		position = cedrus_buf->codec.h264.position;
> 
> 		sram_array[i] |= position << 1;
> 		if (ref_buf->field == V4L2_FIELD_BOTTOM)
> 			sram_array[i] |= BIT(0);
> 	}
> 
> 	cedrus_h264_write_sram(dev, sram, &sram_array, num_ref);
> }
> 
> IMO this code is easier to read.

INdeed, thanks!

> > > > +			const struct v4l2_h264_dpb_entry *dpb;
> > > > +			const struct cedrus_buffer *cedrus_buf;
> > > > +			const struct vb2_v4l2_buffer *ref_buf;
> > > > +			unsigned int position;
> > > > +			int buf_idx;
> > > > +			u8 ref_idx = i + j;
> > > > +			u8 dpb_idx;
> > > > +
> > > > +			if (ref_idx >= num_ref)
> > > > +				break;
> > > > +
> > > > +			dpb_idx = ref_list[ref_idx];
> > > > +			dpb = &decode->dpb[dpb_idx];
> > > > +
> > > > +			if (!(dpb->flags & V4L2_H264_DPB_ENTRY_FLAG_ACTIVE))
> > > > +				continue;
> > > > +
> > > > +			buf_idx = vb2_find_tag(cap_q, dpb->tag, 0);
> > > > +			if (buf_idx < 0)
> > > > +				continue;
> > > > +
> > > > +			ref_buf = to_vb2_v4l2_buffer(ctx->dst_bufs[buf_idx]);
> > > > +			cedrus_buf = vb2_v4l2_to_cedrus_buffer(ref_buf);
> > > > +			position = cedrus_buf->codec.h264.position;
> > > > +
> > > > +			sram_array[i] |= position << (j * 8 + 1);
> > > > +			if (ref_buf->field == V4L2_FIELD_BOTTOM)
> > > 
> > > You newer set above flag to buffer so this will be always false.
> > 
> > As far as I know, the field is supposed to be set by the userspace.
> 
> How? I thought that only flags at queueing buffers can be set and there is no 
> bottom/top flag.

https://linuxtv.org/downloads/v4l-dvb-apis/uapi/v4l/buffer.html#c.v4l2_buffer

"Indicates the field order of the image in the buffer, see
v4l2_field. This field is not used when the buffer contains VBI
data. Drivers must set it when type refers to a capture stream,
applications when it refers to an output stream."

My understanding is that the application should set it, since we'll
use the output stream's buffer here. But I might very well be wrong
about it :/

Maxime

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

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