Re: [PATCH 7/9] media: hantro: Add core bits to support H264 decoding

[Rasmus Villemoes]

On 19/06/2019 14.15, Boris Brezillon wrote:
> From: Hertz Wong <hertz.wong@xxxxxxxxxxxxxx>
> 
> Add helpers and patch hantro_{drv,v4l2}.c to prepare addition of H264
> decoding support.
> 
> Signed-off-by: Hertz Wong <hertz.wong@xxxxxxxxxxxxxx>
> Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> ---
> +
> +	/*
> +	 * Short term pics in descending pic num order, long term ones in
> +	 * ascending order.
> +	 */
> +	if (!(a->flags & V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM))
> +		return b->frame_num - a->frame_num;
> +
> +	return a->pic_num - b->pic_num;
> +}

Pet peeve: This works because ->frame_num and ->pic_num are u16, so
their difference is guaranteed to fit in an int.

> +static int b0_ref_list_cmp(const void *ptra, const void *ptrb, const void *data)
> +{
> +	const struct hantro_h264_reflist_builder *builder = data;
> +	const struct v4l2_h264_dpb_entry *a, *b;
> +	s32 poca, pocb;
> +	u8 idxa, idxb;
> +
> +	idxa = *((u8 *)ptra);
> +	idxb = *((u8 *)ptrb);
> +	a = &builder->dpb[idxa];
> +	b = &builder->dpb[idxb];
> +
> +	if ((a->flags & V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM) !=
> +	    (b->flags & V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM)) {
> +		/* Short term pics firt. */
> +		if (!(a->flags & V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM))
> +			return -1;
> +		else
> +			return 1;
> +	}
> +
> +	/* Long term pics in ascending pic num order. */
> +	if (a->flags & V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM)
> +		return a->pic_num - b->pic_num;
> +
> +	poca = builder->pocs[idxa];
> +	pocb = builder->pocs[idxb];
> +
> +	/*
> +	 * Short term pics with POC < cur POC first in POC descending order
> +	 * followed by short term pics with POC > cur POC in POC ascending
> +	 * order.
> +	 */
> +	if ((poca < builder->curpoc) != (pocb < builder->curpoc))
> +		return poca - pocb;
> +	else if (poca < builder->curpoc)
> +		return pocb - poca;
> +
> +	return poca - pocb;
> +}

Here, however, poca and pocb are ints. What guarantees that their values
are not more than 2^31 apart? I know absolutely nothing about this code
or what these numbers represent, so it may be obvious that they are
smallish.

Rasmus