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

1 files changed, 39 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 5890e0ba2eb9..404bc0ba9475 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/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);