[PATCH 4/4] drm/i915/dp: Disable the AUX DPCD probe quirk if it's not required

[Imre Deak]

Reading DPCD registers has side-effects and some of these can cause a
problem for instance during link training. Based on this it's better to
avoid the probing quirk done before each DPCD register read, limiting
this to the monitor which requires it. The only known problematic
monitor is an external SST sink, so keep the quirk disabled always for
eDP and MST sinks. Reenable the quirk after a hotplug event and after
resuming from a power state without hotplug support, until the
subsequent EDID based detection.

Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c      | 11 +++++++++--
 drivers/gpu/drm/i915/display/intel_dp_aux.c  |  2 ++
 drivers/gpu/drm/i915/display/intel_hotplug.c | 10 ++++++++++
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 208a953b04a2f..d65a18fc1aeb9 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -5747,6 +5747,11 @@ intel_dp_set_edid(struct intel_dp *intel_dp)
 	/* Below we depend on display info having been updated */
 	drm_edid_connector_update(&connector->base, drm_edid);
 
+	if (!intel_dp_is_edp(intel_dp))
+		drm_dp_dpcd_set_probe_quirk(&intel_dp->aux,
+					    drm_edid_has_quirk(&connector->base,
+							       DRM_EDID_QUIRK_DP_DPCD_PROBE));
+
 	vrr_capable = intel_vrr_is_capable(connector);
 	drm_dbg_kms(display->drm, "[CONNECTOR:%d:%s] VRR capable: %s\n",
 		    connector->base.base.id, connector->base.name, str_yes_no(vrr_capable));
@@ -5881,6 +5886,7 @@ intel_dp_detect(struct drm_connector *_connector,
 	intel_dp_print_rates(intel_dp);
 
 	if (intel_dp->is_mst) {
+		drm_dp_dpcd_set_probe_quirk(&intel_dp->aux, false);
 		/*
 		 * If we are in MST mode then this connector
 		 * won't appear connected or have anything
@@ -6321,10 +6327,11 @@ intel_dp_hpd_pulse(struct intel_digital_port *dig_port, bool long_hpd)
 	 * complete the DP tunnel BW request for the latter connector/encoder
 	 * waiting for this encoder's DPRX read, perform a dummy read here.
 	 */
-	if (long_hpd)
+	if (long_hpd) {
+		drm_dp_dpcd_set_probe_quirk(&intel_dp->aux, true);
+
 		intel_dp_read_dprx_caps(intel_dp, dpcd);
 
-	if (long_hpd) {
 		intel_dp->reset_link_params = true;
 		intel_dp_invalidate_source_oui(intel_dp);
 
diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
index bf8e8e0cc19c9..410252ba6fd16 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
@@ -835,6 +835,8 @@ void intel_dp_aux_init(struct intel_dp *intel_dp)
 
 	intel_dp->aux.transfer = intel_dp_aux_transfer;
 	cpu_latency_qos_add_request(&intel_dp->pm_qos, PM_QOS_DEFAULT_VALUE);
+
+	drm_dp_dpcd_set_probe_quirk(&intel_dp->aux, !intel_dp_is_edp(intel_dp));
 }
 
 static enum aux_ch default_aux_ch(struct intel_encoder *encoder)
diff --git a/drivers/gpu/drm/i915/display/intel_hotplug.c b/drivers/gpu/drm/i915/display/intel_hotplug.c
index 74fe398663d63..1093c6c3714c0 100644
--- a/drivers/gpu/drm/i915/display/intel_hotplug.c
+++ b/drivers/gpu/drm/i915/display/intel_hotplug.c
@@ -33,6 +33,7 @@
 #include "intel_display_core.h"
 #include "intel_display_rpm.h"
 #include "intel_display_types.h"
+#include "intel_dp.h"
 #include "intel_hdcp.h"
 #include "intel_hotplug.h"
 #include "intel_hotplug_irq.h"
@@ -906,9 +907,18 @@ void intel_hpd_poll_enable(struct intel_display *display)
  */
 void intel_hpd_poll_disable(struct intel_display *display)
 {
+	struct intel_encoder *encoder;
+
 	if (!HAS_DISPLAY(display))
 		return;
 
+	for_each_intel_dp(display->drm, encoder) {
+		struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
+
+		if (!intel_dp_is_edp(intel_dp))
+			drm_dp_dpcd_set_probe_quirk(&intel_dp->aux, true);
+	}
+
 	WRITE_ONCE(display->hotplug.poll_enabled, false);
 
 	spin_lock_irq(&display->irq.lock);
-- 
2.44.2