drm/dp_helper: Add support for link failure detection

There are specific DPCDs defined for detecting link failures between
the PCON and HDMI sink and check the link status. In case of link
failure, PCON will communicate the same using an IRQ_HPD to source.
HDMI sink would have indicated the same to PCON using SCDC interrupt
mechanism. While source can always read final HDMI sink's status using
I2C over AUX, it is easier and faster to read the PCONs already read
HDMI sink status registers.

This patch adds the DPCDs required for link failure detection and
provide a helper function for printing error count/lane which might
help in debugging the link failure issues.

v2: Addressed comments from Uma Shankar:
-rephrased the commit message, as per the code.
-fixed styling issues
-added documentation for the helper function.
Signed-off-by: Swati Sharma <swati2.sharma@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
[Jani: Fixed checkpatch PARENTHESIS_ALIGNMENT.]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201218103723.30844-6-ankit.k.nautiyal@intel.com

drivers/gpu/drm/drm_dp_helper.c

@@ -2859,3 +2859,42 @@ int drm_dp_pcon_hdmi_link_mode(struct drm_dp_aux *aux, u8 *frl_trained_mask)
 	return mode;
 }
 EXPORT_SYMBOL(drm_dp_pcon_hdmi_link_mode);
+
+/**
+ * drm_dp_pcon_hdmi_frl_link_error_count() - print the error count per lane
+ * during link failure between PCON and HDMI sink
+ * @aux: DisplayPort AUX channel
+ * @connector: DRM connector
+ * code.
+ **/
+
+void drm_dp_pcon_hdmi_frl_link_error_count(struct drm_dp_aux *aux,
+					   struct drm_connector *connector)
+{
+	u8 buf, error_count;
+	int i, num_error;
+	struct drm_hdmi_info *hdmi = &connector->display_info.hdmi;
+
+	for (i = 0; i < hdmi->max_lanes; i++) {
+		if (drm_dp_dpcd_readb(aux, DP_PCON_HDMI_ERROR_STATUS_LN0 + i, &buf) < 0)
+			return;
+
+		error_count = buf & DP_PCON_HDMI_ERROR_COUNT_MASK;
+		switch (error_count) {
+		case DP_PCON_HDMI_ERROR_COUNT_HUNDRED_PLUS:
+			num_error = 100;
+			break;
+		case DP_PCON_HDMI_ERROR_COUNT_TEN_PLUS:
+			num_error = 10;
+			break;
+		case DP_PCON_HDMI_ERROR_COUNT_THREE_PLUS:
+			num_error = 3;
+			break;
+		default:
+			num_error = 0;
+		}
+
+		DRM_ERROR("More than %d errors since the last read for lane %d", num_error, i);
+	}
+}
+EXPORT_SYMBOL(drm_dp_pcon_hdmi_frl_link_error_count);

include/drm/drm_dp_helper.h

@@ -946,6 +946,11 @@ struct drm_device;
 # define DP_CEC_IRQ                          (1 << 2)
 
 #define DP_LINK_SERVICE_IRQ_VECTOR_ESI0     0x2005   /* 1.2 */
+# define RX_CAP_CHANGED                      (1 << 0)
+# define LINK_STATUS_CHANGED                 (1 << 1)
+# define STREAM_STATUS_CHANGED               (1 << 2)
+# define HDMI_LINK_STATUS_CHANGED            (1 << 3)
+# define CONNECTED_OFF_ENTRY_REQUESTED       (1 << 4)
 
 #define DP_PSR_ERROR_STATUS                 0x2006  /* XXX 1.2? */
 # define DP_PSR_LINK_CRC_ERROR              (1 << 0)
@@ -1120,6 +1125,16 @@ struct drm_device;
 #define DP_PROTOCOL_CONVERTER_CONTROL_2		0x3052 /* DP 1.3 */
 # define DP_CONVERSION_TO_YCBCR422_ENABLE	(1 << 0) /* DP 1.3 */
 
+/* PCON Downstream HDMI ERROR Status per Lane */
+#define DP_PCON_HDMI_ERROR_STATUS_LN0          0x3037
+#define DP_PCON_HDMI_ERROR_STATUS_LN1          0x3038
+#define DP_PCON_HDMI_ERROR_STATUS_LN2          0x3039
+#define DP_PCON_HDMI_ERROR_STATUS_LN3          0x303A
+# define DP_PCON_HDMI_ERROR_COUNT_MASK         (0x7 << 0)
+# define DP_PCON_HDMI_ERROR_COUNT_THREE_PLUS   (1 << 0)
+# define DP_PCON_HDMI_ERROR_COUNT_TEN_PLUS     (1 << 1)
+# define DP_PCON_HDMI_ERROR_COUNT_HUNDRED_PLUS (1 << 2)
+
 /* HDCP 1.3 and HDCP 2.2 */
 #define DP_AUX_HDCP_BKSV		0x68000
 #define DP_AUX_HDCP_RI_PRIME		0x68005
@@ -2036,5 +2051,7 @@ int drm_dp_pcon_frl_enable(struct drm_dp_aux *aux);
 
 bool drm_dp_pcon_hdmi_link_active(struct drm_dp_aux *aux);
 int drm_dp_pcon_hdmi_link_mode(struct drm_dp_aux *aux, u8 *frl_trained_mask);
+void drm_dp_pcon_hdmi_frl_link_error_count(struct drm_dp_aux *aux,
+					   struct drm_connector *connector);
 
 #endif /* _DRM_DP_HELPER_H_ */