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Date:   Tue, 21 Feb 2017 18:19:35 -0800
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Thibault Saunier <thibault.saunier@....samsung.com>,
        linux-kernel@...r.kernel.org
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kukjin Kim <kgene@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Andi Shyti <andi.shyti@...sung.com>,
        linux-media@...r.kernel.org, Shuah Khan <shuahkh@....samsung.com>,
        Javier Martinez Canillas <javier@....samsung.com>,
        linux-samsung-soc@...r.kernel.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Inki Dae <inki.dae@...sung.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        linux-arm-kernel@...ts.infradead.org,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Hans Verkuil <hans.verkuil@...co.com>
Subject: Re: [PATCH v5 1/3] [media] exynos-gsc: Use user configured colorspace
 if provided



On 02/21/2017 11:20 AM, Thibault Saunier wrote:
> Use colorspace provided by the user as we are only doing scaling and
> color encoding conversion, we won't be able to transform the colorspace
> itself and the colorspace won't mater in that operation.
> 
> Also always use output colorspace on the capture side.
> 
> Start using 576p as a threashold to compute the colorspace.
> The media documentation says that the V4L2_COLORSPACE_SMPTE170M colorspace
> should be used for SDTV and V4L2_COLORSPACE_REC709 for HDTV. But drivers
> don't agree on the display resolution that should be used as a threshold.
> 
> From EIA CEA 861B about colorimetry for various resolutions:
> 
>   - 5.1 480p, 480i, 576p, 576i, 240p, and 288p
>     The color space used by the 480-line, 576-line, 240-line, and 288-line
>     formats will likely be based on SMPTE 170M [1].
>   - 5.2 1080i, 1080p, and 720p
>     The color space used by the high definition formats will likely be
>     based on ITU-R BT.709-4
> 
> This indicates that in the case that userspace does not specify what
> colorspace should be used, we should use 576p  as a threshold to set
> V4L2_COLORSPACE_REC709 instead of V4L2_COLORSPACE_SMPTE170M. Even if it is
> only 'likely' and not a requirement it is the best guess we can make.
> 
> The stream should have been encoded with the information and userspace
> has to pass it to the driver if it is not the case, otherwise we won't be
> able to handle it properly anyhow.
> 
> Also, check for the resolution in G_FMT instead unconditionally setting
> the V4L2_COLORSPACE_REC709 colorspace.
> 
> Signed-off-by: Javier Martinez Canillas <javier@....samsung.com>
> Signed-off-by: Thibault Saunier <thibault.saunier@....samsung.com>
> Reviewed-by: Andrzej Hajda <a.hajda@...sung.com>
> 
> ---
> 
> Changes in v5:
> - Squash commit to always use output colorspace on the capture side
>   inside this one
> - Fix typo in commit message
> 
> Changes in v4:
> - Reword commit message to better back our assumptions on specifications
> 
> Changes in v3:
> - Do not check values in the g_fmt functions as Andrzej explained in previous review
> - Added 'Reviewed-by: Andrzej Hajda <a.hajda@...sung.com>'
> 
> Changes in v2: None
> 
>  drivers/media/platform/exynos-gsc/gsc-core.c | 20 +++++++++++++++-----
>  drivers/media/platform/exynos-gsc/gsc-core.h |  1 +
>  2 files changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/media/platform/exynos-gsc/gsc-core.c b/drivers/media/platform/exynos-gsc/gsc-core.c
> index 59a634201830..772599de8c13 100644
> --- a/drivers/media/platform/exynos-gsc/gsc-core.c
> +++ b/drivers/media/platform/exynos-gsc/gsc-core.c
> @@ -454,6 +454,7 @@ int gsc_try_fmt_mplane(struct gsc_ctx *ctx, struct v4l2_format *f)
>  	} else {
>  		min_w = variant->pix_min->target_rot_dis_w;
>  		min_h = variant->pix_min->target_rot_dis_h;
> +		pix_mp->colorspace = ctx->out_colorspace;
>  	}
>  
>  	pr_debug("mod_x: %d, mod_y: %d, max_w: %d, max_h = %d",
> @@ -472,10 +473,15 @@ int gsc_try_fmt_mplane(struct gsc_ctx *ctx, struct v4l2_format *f)
>  
>  	pix_mp->num_planes = fmt->num_planes;
>  
> -	if (pix_mp->width >= 1280) /* HD */
> -		pix_mp->colorspace = V4L2_COLORSPACE_REC709;
> -	else /* SD */
> -		pix_mp->colorspace = V4L2_COLORSPACE_SMPTE170M;
> +	if (pix_mp->colorspace == V4L2_COLORSPACE_DEFAULT) {
> +		if (pix_mp->width > 720 && pix_mp->height > 576) /* HD */

I'd use || instead of && here. Ditto for the next patch.

> +			pix_mp->colorspace = V4L2_COLORSPACE_REC709;
> +		else /* SD */
> +			pix_mp->colorspace = V4L2_COLORSPACE_SMPTE170M;
> +	}

Are you sure this is in fact how it is used? If the source of the video
is the sensor (camera), then the colorspace is typically SRGB. I'm not
really sure you should guess here. All a mem2mem driver should do is to
pass the colorspace etc. information from the output to the capture side,
and not invent things. That simply makes no sense.

We may have to update the documentation or v4l2-compliance test if this
is an issue. The more I think about this, the more I think we shouldn't
do this guessing game.

Regards,

	Hans

> +
> +	if (V4L2_TYPE_IS_OUTPUT(f->type))
> +		ctx->out_colorspace = pix_mp->colorspace;
>  
>  	for (i = 0; i < pix_mp->num_planes; ++i) {
>  		struct v4l2_plane_pix_format *plane_fmt = &pix_mp->plane_fmt[i];
> @@ -519,9 +525,13 @@ int gsc_g_fmt_mplane(struct gsc_ctx *ctx, struct v4l2_format *f)
>  	pix_mp->height		= frame->f_height;
>  	pix_mp->field		= V4L2_FIELD_NONE;
>  	pix_mp->pixelformat	= frame->fmt->pixelformat;
> -	pix_mp->colorspace	= V4L2_COLORSPACE_REC709;
>  	pix_mp->num_planes	= frame->fmt->num_planes;
>  
> +	if (pix_mp->width > 720 && pix_mp->height > 576) /* HD */
> +		pix_mp->colorspace = V4L2_COLORSPACE_REC709;
> +	else /* SD */
> +		pix_mp->colorspace = V4L2_COLORSPACE_SMPTE170M;
> +
>  	for (i = 0; i < pix_mp->num_planes; ++i) {
>  		pix_mp->plane_fmt[i].bytesperline = (frame->f_width *
>  			frame->fmt->depth[i]) / 8;
> diff --git a/drivers/media/platform/exynos-gsc/gsc-core.h b/drivers/media/platform/exynos-gsc/gsc-core.h
> index 696217e9af66..715d9c9d8d30 100644
> --- a/drivers/media/platform/exynos-gsc/gsc-core.h
> +++ b/drivers/media/platform/exynos-gsc/gsc-core.h
> @@ -376,6 +376,7 @@ struct gsc_ctx {
>  	struct v4l2_ctrl_handler ctrl_handler;
>  	struct gsc_ctrls	gsc_ctrls;
>  	bool			ctrls_rdy;
> +	enum v4l2_colorspace out_colorspace;
>  };
>  
>  void gsc_set_prefbuf(struct gsc_dev *gsc, struct gsc_frame *frm);
> 

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