Re: [PATCHv2 2/2] v4l: vsp1: Add HGT support

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Niklas,

Thank you for the patch.

On Tuesday 06 Sep 2016 16:38:56 Niklas Söderlund wrote:
> The HGT is a Histogram Generator Two-Dimensions. It computes a weighted
> frequency histograms for hue and saturation areas over a configurable
> region of the image with optional subsampling.
> 
> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
> ---
>  drivers/media/platform/vsp1/Makefile      |   2 +-
>  drivers/media/platform/vsp1/vsp1.h        |   3 +
>  drivers/media/platform/vsp1/vsp1_drv.c    |  33 ++++-
>  drivers/media/platform/vsp1/vsp1_entity.c |  33 +++--
>  drivers/media/platform/vsp1/vsp1_entity.h |   1 +
>  drivers/media/platform/vsp1/vsp1_hgt.c    | 217 +++++++++++++++++++++++++++
>  drivers/media/platform/vsp1/vsp1_hgt.h    |  42 ++++++
>  drivers/media/platform/vsp1/vsp1_pipe.c   |  16 +++
>  drivers/media/platform/vsp1/vsp1_pipe.h   |   2 +
>  drivers/media/platform/vsp1/vsp1_regs.h   |   9 ++
>  drivers/media/platform/vsp1/vsp1_video.c  |  10 +-
>  11 files changed, 352 insertions(+), 16 deletions(-)
>  create mode 100644 drivers/media/platform/vsp1/vsp1_hgt.c
>  create mode 100644 drivers/media/platform/vsp1/vsp1_hgt.h

[snip]

> diff --git a/drivers/media/platform/vsp1/vsp1_hgt.c
> b/drivers/media/platform/vsp1/vsp1_hgt.c new file mode 100644
> index 0000000..4e3f762
> --- /dev/null
> +++ b/drivers/media/platform/vsp1/vsp1_hgt.c

[snip]

> +/* ------------------------------------------------------------------------
> + * Controls
> + */
> +
> +#define V4L2_CID_VSP1_HGT_HUE_AREAS	(V4L2_CID_USER_BASE | 0x1001)
> +
> +static int hgt_hue_areas_s_ctrl(struct v4l2_ctrl *ctrl)
> +{
> +	struct vsp1_hgt *hgt = container_of(ctrl->handler, struct vsp1_hgt,
> +					    ctrls);
> +	u8 *value = ctrl->p_new.p_u8;

Nitpicking, I'd call the variable values.

> +	unsigned int i;
> +	bool ok = true;
> +
> +	/*
> +	 * Make sure values meet one of two possible hardware constrains

s/constrains/constraints./

> +	 * 0L <= 0U <= 1L <= 1U <= 2L <= 2U <= 3L <= 3U <= 4L <= 4U <= 5L <= 
5U
> +	 * 0U <= 1L <= 1U <= 2L <= 2U <= 3L <= 3U <= 4L <= 4U <= 5L <= 5U <= 
0L
> +	 */
> +
> +	if ((value[0] > value[1]) && (value[11] > value[0]))
> +		ok = false;
> +	for (i = 1; i < (HGT_NUM_HUE_AREAS * 2) - 1; ++i)
> +		if (value[i] > value[i+1])
> +			ok = false;
> +
> +	/* Values do not match hardware, adjust to valid settings. */
> +	if (!ok) {
> +		for (i = 0; i < (HGT_NUM_HUE_AREAS * 2) - 1; ++i) {
> +			if (value[i] > value[i+1])
> +				value[i] = value[i+1];
> +		}
> +	}

I'm afraid this won't work. Let's assume value[0] = 100, value[1] = 50, 
value[2] = 25. The loop will unroll to

	if (value[0] /* 100 */ > value[1] /* 50 */)
		value[0] = value[1] /* 50 */;
	if (value[1] /* 50 */ > value[2] /* 25 */)
		value[1] = value[2] /* 25 */;

You will end up with value[0] = 50, value[1] = 25, value[2] = 25, which 
doesn't match the hardware constraints.

How about the following, which tests and fixes the values in a single 
operation ?

static int hgt_hue_areas_s_ctrl(struct v4l2_ctrl *ctrl)
{
	struct vsp1_hgt *hgt = container_of(ctrl->handler, struct vsp1_hgt,
					    ctrls);
	u8 *values = ctrl->p_new.p_u8;
	unsigned int i;
        
	/*
	 * Adjust the values if they don't meet the hardware constraints:
	 *
	 * 0U <= 1L <= 1U <= 2L <= 2U <= 3L <= 3U <= 4L <= 4U <= 5L <= 5U
	 */ 
	for (i = 1; i < (HGT_NUM_HUE_AREAS * 2) - 1; ++i) {
		if (values[i] > values[i+1])
			values[i+1] = values[i];
	}
        
	/* 0L <= 0U or 5U <= 0L */
	if (values[0] > values[1] && values[11] > values[0])
		values[0] = values[1];
        
	memcpy(hgt->hue_areas, ctrl->p_new.p_u8, sizeof(hgt->hue_areas));

	return 0;
}

I'm also beginning to wonder whether it wouldn't make sense to return -EINVAL 
when the values don't match the constraints instead of trying to fix them.

> +	memcpy(hgt->hue_areas, ctrl->p_new.p_u8, sizeof(hgt->hue_areas));
> +
> +	return 0;
> +}

[snip]

-- 
Regards,

Laurent Pinchart