linux-kernel - Printing bitfields in the kernel (Re: [PATCH] drm: Parse Colorimetry data block from EDID)

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Date:   Thu, 27 Aug 2020 10:34:56 +0300
From:   Pekka Paalanen <ppaalanen@...il.com>
To:     Algea Cao <algea.cao@...k-chips.com>
Cc:     mripard@...nel.org, tzimmermann@...e.de,
        linux-kernel@...r.kernel.org, airlied@...ux.ie,
        dri-devel@...ts.freedesktop.org, maarten.lankhorst@...ux.intel.com,
        daniel@...ll.ch, linux-rockchip@...ts.infradead.org
Subject: Printing bitfields in the kernel (Re: [PATCH] drm: Parse
 Colorimetry data block from EDID)

On Wed, 26 Aug 2020 22:23:28 +0800
Algea Cao <algea.cao@...k-chips.com> wrote:

> CEA 861.3 spec adds colorimetry data block for HDMI.
> Parsing the block to get the colorimetry data from
> panel.
> 
> Signed-off-by: Algea Cao <algea.cao@...k-chips.com>
> ---
> 
>  drivers/gpu/drm/drm_edid.c  | 45 +++++++++++++++++++++++++++++++++++++
>  include/drm/drm_connector.h |  3 +++
>  include/drm/drm_edid.h      | 14 ++++++++++++
>  3 files changed, 62 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 31496b6cfc56..67e607c04492 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -3223,6 +3223,7 @@ add_detailed_modes(struct drm_connector *connector, struct edid *edid,
>  #define VIDEO_BLOCK     0x02
>  #define VENDOR_BLOCK    0x03
>  #define SPEAKER_BLOCK	0x04
> +#define COLORIMETRY_DATA_BLOCK		0x5
>  #define HDR_STATIC_METADATA_BLOCK	0x6
>  #define USE_EXTENDED_TAG 0x07
>  #define EXT_VIDEO_CAPABILITY_BLOCK 0x00
> @@ -4309,6 +4310,48 @@ static void fixup_detailed_cea_mode_clock(struct drm_display_mode *mode)
>  	mode->clock = clock;
>  }
>  
> +static bool cea_db_is_hdmi_colorimetry_data_block(const u8 *db)
> +{
> +	if (cea_db_tag(db) != USE_EXTENDED_TAG)
> +		return false;
> +
> +	if (db[1] != COLORIMETRY_DATA_BLOCK)
> +		return false;
> +
> +	if (cea_db_payload_len(db) < 2)
> +		return false;
> +
> +	return true;
> +}
> +
> +static void
> +drm_parse_colorimetry_data_block(struct drm_connector *connector, const u8 *db)
> +{
> +	struct drm_hdmi_info *info = &connector->display_info.hdmi;
> +
> +	if (db[2] & DRM_EDID_CLRMETRY_xvYCC_601)
> +		info->colorimetry |= DRM_EDID_CLRMETRY_xvYCC_601;
> +	if (db[2] & DRM_EDID_CLRMETRY_xvYCC_709)
> +		info->colorimetry |= DRM_EDID_CLRMETRY_xvYCC_709;
> +	if (db[2] & DRM_EDID_CLRMETRY_sYCC_601)
> +		info->colorimetry |= DRM_EDID_CLRMETRY_sYCC_601;
> +	if (db[2] & DRM_EDID_CLRMETRY_ADBYCC_601)
> +		info->colorimetry |= DRM_EDID_CLRMETRY_ADBYCC_601;
> +	if (db[2] & DRM_EDID_CLRMETRY_ADB_RGB)
> +		info->colorimetry |= DRM_EDID_CLRMETRY_ADB_RGB;
> +	if (db[2] & DRM_EDID_CLRMETRY_BT2020_CYCC)
> +		info->colorimetry |= DRM_EDID_CLRMETRY_BT2020_CYCC;
> +	if (db[2] & DRM_EDID_CLRMETRY_BT2020_YCC)
> +		info->colorimetry |= DRM_EDID_CLRMETRY_BT2020_YCC;
> +	if (db[2] & DRM_EDID_CLRMETRY_BT2020_RGB)
> +		info->colorimetry |= DRM_EDID_CLRMETRY_BT2020_RGB;
> +	/* Byte 4 Bit 7: DCI-P3 */
> +	if (db[3] & BIT(7))
> +		info->colorimetry |= DRM_EDID_CLRMETRY_DCI_P3;
> +
> +	DRM_DEBUG_KMS("Supported Colorimetry 0x%x\n", info->colorimetry);

Hi,

taking a tangent here, printing bitfields as hex is hard to read. How
about using something like nvkm_snprintbf()? Of course not literally
that function since it's Nouveau internal, but as an end user I would be
happy to see DRM core or the kernel generics have similar functionality
that actually decodes the bits and prints their proper names.

Does such facility not exist yet?


Thanks,
pq

> +}
> +
>  static bool cea_db_is_hdmi_hdr_metadata_block(const u8 *db)
>  {
>  	if (cea_db_tag(db) != USE_EXTENDED_TAG)
> @@ -4994,6 +5037,8 @@ static void drm_parse_cea_ext(struct drm_connector *connector,
>  			drm_parse_vcdb(connector, db);
>  		if (cea_db_is_hdmi_hdr_metadata_block(db))
>  			drm_parse_hdr_metadata_block(connector, db);
> +		if (cea_db_is_hdmi_colorimetry_data_block(db))
> +			drm_parse_colorimetry_data_block(connector, db);
>  	}
>  }
>  
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index af145608b5ed..d599c3b9e881 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -207,6 +207,9 @@ struct drm_hdmi_info {
>  
>  	/** @y420_dc_modes: bitmap of deep color support index */
>  	u8 y420_dc_modes;
> +
> +	/* @colorimetry: bitmap of supported colorimetry modes */
> +	u16 colorimetry;
>  };
>  
>  /**
> diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
> index cfa4f5af49af..98fa78c2f82d 100644
> --- a/include/drm/drm_edid.h
> +++ b/include/drm/drm_edid.h
> @@ -229,6 +229,20 @@ struct detailed_timing {
>  				    DRM_EDID_YCBCR420_DC_36 | \
>  				    DRM_EDID_YCBCR420_DC_30)
>  
> +/*
> + * Supported Colorimetry from colorimetry data block
> + * as per CEA 861-G spec
> + */
> +#define DRM_EDID_CLRMETRY_xvYCC_601   (1 << 0)
> +#define DRM_EDID_CLRMETRY_xvYCC_709   (1 << 1)
> +#define DRM_EDID_CLRMETRY_sYCC_601    (1 << 2)
> +#define DRM_EDID_CLRMETRY_ADBYCC_601  (1 << 3)
> +#define DRM_EDID_CLRMETRY_ADB_RGB     (1 << 4)
> +#define DRM_EDID_CLRMETRY_BT2020_CYCC (1 << 5)
> +#define DRM_EDID_CLRMETRY_BT2020_YCC  (1 << 6)
> +#define DRM_EDID_CLRMETRY_BT2020_RGB  (1 << 7)
> +#define DRM_EDID_CLRMETRY_DCI_P3      (1 << 15)
> +
>  /* ELD Header Block */
>  #define DRM_ELD_HEADER_BLOCK_SIZE	4
>  


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