[PATCH v4 1/4] [media] exynos-gsc: Use 576p instead 720p as a threshold for colorspaces

[Thibault Saunier <thibault.saunier@osg.samsung.com>]

From: Javier Martinez Canillas <javier@osg.samsung.com>

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_REC709. 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@osg.samsung.com>
Signed-off-by: Thibault Saunier <thibault.saunier@osg.samsung.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>

---

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@samsung.com>'

Changes in v2: None

 drivers/media/platform/exynos-gsc/gsc-core.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/media/platform/exynos-gsc/gsc-core.c b/drivers/media/platform/exynos-gsc/gsc-core.c
index 59a634201830..db7d9883861b 100644
--- a/drivers/media/platform/exynos-gsc/gsc-core.c
+++ b/drivers/media/platform/exynos-gsc/gsc-core.c
@@ -472,7 +472,7 @@ 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 */
+	if (pix_mp->width > 720 && pix_mp->height > 576) /* HD */
 		pix_mp->colorspace = V4L2_COLORSPACE_REC709;
 	else /* SD */
 		pix_mp->colorspace = V4L2_COLORSPACE_SMPTE170M;
@@ -519,9 +519,13 @@ 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;
-- 
2.11.1