drm/dp_helper: Add helpers to configure PCONs RGB-YCbCr Conversion

DP Specification for DP2.0 to HDMI2.1 Pcon specifies support for conversion
of colorspace from RGB to YCbCr.
https://groups.vesa.org/wg/DP/document/previewpdf/15651

This patch adds the relavant registers and helper functions to
get the capability and set the color conversion bits for rgb->ycbcr
conversion through PCON.

v2: As suggested in review comments:
-Fixed bug in the check condition in a drm_helper as reported by
 Dan Carpenter and Kernel test robot. (Dan Carepenter)
-Modified the color-conversion cap helper function, to accommodate
 BT709 and BT2020 colorspace. (Uma Shankar)
-Added spec details for the new cap for color conversion. (Uma Shankar)
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201218103723.30844-8-ankit.k.nautiyal@intel.com

drivers/gpu/drm/drm_dp_helper.c

@@ -949,6 +949,38 @@ bool drm_dp_downstream_444_to_420_conversion(const u8 dpcd[DP_RECEIVER_CAP_SIZE]
 }
 EXPORT_SYMBOL(drm_dp_downstream_444_to_420_conversion);
 
+/**
+ * drm_dp_downstream_rgb_to_ycbcr_conversion() - determine downstream facing port
+ *                                               RGB->YCbCr conversion capability
+ * @dpcd: DisplayPort configuration data
+ * @port_cap: downstream facing port capabilities
+ * @colorspc: Colorspace for which conversion cap is sought
+ *
+ * Returns: whether the downstream facing port can convert RGB->YCbCr for a given
+ * colorspace.
+ */
+bool drm_dp_downstream_rgb_to_ycbcr_conversion(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
+					       const u8 port_cap[4],
+					       u8 color_spc)
+{
+	if (!drm_dp_is_branch(dpcd))
+		return false;
+
+	if (dpcd[DP_DPCD_REV] < 0x13)
+		return false;
+
+	switch (port_cap[0] & DP_DS_PORT_TYPE_MASK) {
+	case DP_DS_PORT_TYPE_HDMI:
+		if ((dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DETAILED_CAP_INFO_AVAILABLE) == 0)
+			return false;
+
+		return port_cap[3] & color_spc;
+	default:
+		return false;
+	}
+}
+EXPORT_SYMBOL(drm_dp_downstream_rgb_to_ycbcr_conversion);
+
 /**
  * drm_dp_downstream_mode() - return a mode for downstream facing port
  * @dev: DRM device
@@ -3101,3 +3133,32 @@ int drm_dp_pcon_pps_override_param(struct drm_dp_aux *aux, u8 pps_param[6])
 	return 0;
 }
 EXPORT_SYMBOL(drm_dp_pcon_pps_override_param);
+
+/*
+ * drm_dp_pcon_convert_rgb_to_ycbcr() - Configure the PCon to convert RGB to Ycbcr
+ * @aux: displayPort AUX channel
+ * @color_spc: Color-space/s for which conversion is to be enabled, 0 for disable.
+ *
+ * Returns 0 on success, else returns negative error code.
+ */
+int drm_dp_pcon_convert_rgb_to_ycbcr(struct drm_dp_aux *aux, u8 color_spc)
+{
+	int ret;
+	u8 buf;
+
+	ret = drm_dp_dpcd_readb(aux, DP_PROTOCOL_CONVERTER_CONTROL_2, &buf);
+	if (ret < 0)
+		return ret;
+
+	if (color_spc & DP_CONVERSION_RGB_YCBCR_MASK)
+		buf |= (color_spc & DP_CONVERSION_RGB_YCBCR_MASK);
+	else
+		buf &= ~DP_CONVERSION_RGB_YCBCR_MASK;
+
+	ret = drm_dp_dpcd_writeb(aux, DP_PROTOCOL_CONVERTER_CONTROL_2, buf);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_pcon_convert_rgb_to_ycbcr);

include/drm/drm_dp_helper.h

@@ -432,6 +432,17 @@ struct drm_device;
 # define DP_DS_HDMI_YCBCR444_TO_422_CONV    (1 << 3)
 # define DP_DS_HDMI_YCBCR444_TO_420_CONV    (1 << 4)
 
+/*
+ * VESA DP-to-HDMI PCON Specification adds caps for colorspace
+ * conversion in DFP cap DPCD 83h. Sec6.1 Table-3.
+ * Based on the available support the source can enable
+ * color conversion by writing into PROTOCOL_COVERTER_CONTROL_2
+ * DPCD 3052h.
+ */
+# define DP_DS_HDMI_BT601_RGB_YCBCR_CONV    (1 << 5)
+# define DP_DS_HDMI_BT709_RGB_YCBCR_CONV    (1 << 6)
+# define DP_DS_HDMI_BT2020_RGB_YCBCR_CONV   (1 << 7)
+
 #define DP_MAX_DOWNSTREAM_PORTS		    0x10
 
 /* DP Forward error Correction Registers */
@@ -1207,7 +1218,10 @@ struct drm_device;
 # define DP_PCON_ENC_PPS_OVERRIDE_DISABLED      0
 # define DP_PCON_ENC_PPS_OVERRIDE_EN_PARAMS     1
 # define DP_PCON_ENC_PPS_OVERRIDE_EN_BUFFER     2
-
+# define DP_CONVERSION_RGB_YCBCR_MASK	       (7 << 4)
+# define DP_CONVERSION_BT601_RGB_YCBCR_ENABLE  (1 << 4)
+# define DP_CONVERSION_BT709_RGB_YCBCR_ENABLE  (1 << 5)
+# define DP_CONVERSION_BT2020_RGB_YCBCR_ENABLE (1 << 6)
 
 /* PCON Downstream HDMI ERROR Status per Lane */
 #define DP_PCON_HDMI_ERROR_STATUS_LN0          0x3037
@@ -2167,5 +2181,8 @@ int drm_dp_pcon_dsc_bpp_incr(const u8 pcon_dsc_dpcd[DP_PCON_DSC_ENCODER_CAP_SIZE
 int drm_dp_pcon_pps_default(struct drm_dp_aux *aux);
 int drm_dp_pcon_pps_override_buf(struct drm_dp_aux *aux, u8 pps_buf[128]);
 int drm_dp_pcon_pps_override_param(struct drm_dp_aux *aux, u8 pps_param[6]);
+bool drm_dp_downstream_rgb_to_ycbcr_conversion(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
+					       const u8 port_cap[4], u8 color_spc);
+int drm_dp_pcon_convert_rgb_to_ycbcr(struct drm_dp_aux *aux, u8 color_spc);
 
 #endif /* _DRM_DP_HELPER_H_ */