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Date:   Fri, 4 Sep 2020 06:03:36 +0300
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Adam Goode <agoode@google.com>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] media: uvcvideo: Convey full colorspace information
 to V4L2
Message-ID: <20200904030336.GG9369@pendragon.ideasonboard.com>
References: <20200828032752.3229698-1-agoode@google.com>
 <20200902200617.1720599-1-agoode@google.com>
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Hi Adam,

Thank you for the patch.

On Wed, Sep 02, 2020 at 04:06:17PM -0400, Adam Goode wrote:
> The Color Matching Descriptor has been present in USB cameras since
> the original version of UVC, but it has never been fully exposed
> in Linux.
> 
> This change informs V4L2 of all of the UVC colorspace parameters:
> color primaries, transfer characteristics, and YCbCr encoding.
> videodev2.h doesn't have values for all the possible UVC color settings,
> so it is mapped as closely as possible.
> 
> Signed-off-by: Adam Goode <agoode@google.com>
> ---
> 
> Changes in v3:
>  - Remove quantization changes completely.
> 
>  drivers/media/usb/uvc/uvc_driver.c | 64 ++++++++++++++++++++++++++++--
>  drivers/media/usb/uvc/uvc_v4l2.c   |  4 ++
>  drivers/media/usb/uvc/uvcvideo.h   |  4 +-
>  3 files changed, 67 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index 431d86e1c94b..8682c7ad6949 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -248,10 +248,10 @@ static struct uvc_format_desc *uvc_format_by_guid(const u8 guid[16])
>  	return NULL;
>  }
>  
> -static u32 uvc_colorspace(const u8 primaries)
> +static enum v4l2_colorspace uvc_colorspace(const u8 primaries)
>  {
> -	static const u8 colorprimaries[] = {
> -		0,
> +	static const enum v4l2_colorspace colorprimaries[] = {
> +		V4L2_COLORSPACE_DEFAULT,  /* Unspecified */
>  		V4L2_COLORSPACE_SRGB,
>  		V4L2_COLORSPACE_470_SYSTEM_M,
>  		V4L2_COLORSPACE_470_SYSTEM_BG,
> @@ -262,7 +262,61 @@ static u32 uvc_colorspace(const u8 primaries)
>  	if (primaries < ARRAY_SIZE(colorprimaries))
>  		return colorprimaries[primaries];
>  
> -	return 0;
> +	return V4L2_COLORSPACE_DEFAULT;  /* Reserved */
> +}
> +
> +static enum v4l2_xfer_func uvc_xfer_func(const u8 transfer_characteristics)
> +{
> +	/* V4L2 currently does not currently have definitions for all

A single "currently" should be enough :-) I'll fix this when applying.

> +	 * possible values of UVC transfer characteristics. If
> +	 * v4l2_xfer_func is extended with new values, the mapping
> +	 * below should be updated.
> +	 *
> +	 * Substitutions are taken from the mapping given for
> +	 * V4L2_XFER_FUNC_DEFAULT documented in videodev2.h.
> +	 */
> +	static const enum v4l2_xfer_func xfer_funcs[] = {
> +		V4L2_XFER_FUNC_DEFAULT,    /* Unspecified */
> +		V4L2_XFER_FUNC_709,
> +		V4L2_XFER_FUNC_709,        /* Substitution for BT.470-2 M */
> +		V4L2_XFER_FUNC_709,        /* Substitution for BT.470-2 B, G */
> +		V4L2_XFER_FUNC_709,        /* Substitution for SMPTE 170M */
> +		V4L2_XFER_FUNC_SMPTE240M,
> +		V4L2_XFER_FUNC_NONE,
> +		V4L2_XFER_FUNC_SRGB,
> +	};
> +
> +	if (transfer_characteristics < ARRAY_SIZE(xfer_funcs))
> +		return xfer_funcs[transfer_characteristics];
> +
> +	return V4L2_XFER_FUNC_DEFAULT;  /* Reserved */
> +}
> +
> +static enum v4l2_ycbcr_encoding uvc_ycbcr_enc(const u8 matrix_coefficients)
> +{
> +	/* V4L2 currently does not currently have definitions for all

Same here.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> +	 * possible values of UVC matrix coefficients. If
> +	 * v4l2_ycbcr_encoding is extended with new values, the
> +	 * mapping below should be updated.
> +	 *
> +	 * Substitutions are taken from the mapping given for
> +	 * V4L2_YCBCR_ENC_DEFAULT documented in videodev2.h.
> +	 *
> +	 * FCC is assumed to be close enough to 601.
> +	 */
> +	static const enum v4l2_ycbcr_encoding ycbcr_encs[] = {
> +		V4L2_YCBCR_ENC_DEFAULT,  /* Unspecified */
> +		V4L2_YCBCR_ENC_709,
> +		V4L2_YCBCR_ENC_601,      /* Substitution for FCC */
> +		V4L2_YCBCR_ENC_601,      /* Substitution for BT.470-2 B, G */
> +		V4L2_YCBCR_ENC_601,
> +		V4L2_YCBCR_ENC_SMPTE240M,
> +	};
> +
> +	if (matrix_coefficients < ARRAY_SIZE(ycbcr_encs))
> +		return ycbcr_encs[matrix_coefficients];
> +
> +	return V4L2_YCBCR_ENC_DEFAULT;  /* Reserved */
>  }
>  
>  /* Simplify a fraction using a simple continued fraction decomposition. The
> @@ -704,6 +758,8 @@ static int uvc_parse_format(struct uvc_device *dev,
>  		}
>  
>  		format->colorspace = uvc_colorspace(buffer[3]);
> +		format->xfer_func = uvc_xfer_func(buffer[4]);
> +		format->ycbcr_enc = uvc_ycbcr_enc(buffer[5]);
>  
>  		buflen -= buffer[0];
>  		buffer += buffer[0];
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index 0335e69b70ab..dee65e89d6c2 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -253,6 +253,8 @@ static int uvc_v4l2_try_format(struct uvc_streaming *stream,
>  	fmt->fmt.pix.bytesperline = uvc_v4l2_get_bytesperline(format, frame);
>  	fmt->fmt.pix.sizeimage = probe->dwMaxVideoFrameSize;
>  	fmt->fmt.pix.colorspace = format->colorspace;
> +	fmt->fmt.pix.xfer_func = format->xfer_func;
> +	fmt->fmt.pix.ycbcr_enc = format->ycbcr_enc;
>  
>  	if (uvc_format != NULL)
>  		*uvc_format = format;
> @@ -289,6 +291,8 @@ static int uvc_v4l2_get_format(struct uvc_streaming *stream,
>  	fmt->fmt.pix.bytesperline = uvc_v4l2_get_bytesperline(format, frame);
>  	fmt->fmt.pix.sizeimage = stream->ctrl.dwMaxVideoFrameSize;
>  	fmt->fmt.pix.colorspace = format->colorspace;
> +	fmt->fmt.pix.xfer_func = format->xfer_func;
> +	fmt->fmt.pix.ycbcr_enc = format->ycbcr_enc;
>  
>  done:
>  	mutex_unlock(&stream->mutex);
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index 6ab972c643e3..eb5f3ffc0222 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -370,7 +370,9 @@ struct uvc_format {
>  	u8 type;
>  	u8 index;
>  	u8 bpp;
> -	u8 colorspace;
> +	enum v4l2_colorspace colorspace;
> +	enum v4l2_xfer_func xfer_func;
> +	enum v4l2_ycbcr_encoding ycbcr_enc;
>  	u32 fcc;
>  	u32 flags;
>  

-- 
Regards,

Laurent Pinchart