RE: [PATCHv3] drm/i915/dp: On DPCD init wake the DPRx for eDP

-----Original Message-----
From: Murthy, Arun R <[email protected]> 
Sent: 25 February 2026 11:41
To: [email protected]; [email protected]
Cc: Deak, Imre <[email protected]>; Kandpal, Suraj <[email protected]>; Nikula, Jani <[email protected]>; [email protected]; Murthy, Arun R <[email protected]>
Subject: [PATCHv3] drm/i915/dp: On DPCD init wake the DPRx for eDP

Its observed that on AUX_CH failure, even if the retry is increased to 1000, it does not succeed. Either the command might be wrong or sink in an unknown/sleep state can cause this. So try waking the sink device.
Before reading the DPCD caps wake the sink for eDP.

v2: Use poll_timeout_us (Jani N)
    Add the reason, why this change is required (Ville)
v3: Wake sink only for eDP
    Remove the dpcd probe set to true/false in wake_sink (Imre)

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/4391
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16654
Signed-off-by: Arun R Murthy <[email protected]>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 34 +++++++++++++++++++++++++  drivers/gpu/drm/i915/display/intel_dp.h |  1 +
 2 files changed, 35 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 025e906b63a9..38ea4aad74de 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -4705,6 +4705,38 @@ intel_edp_set_sink_rates(struct intel_dp *intel_dp)
 	intel_edp_set_data_override_rates(intel_dp);
 }
 
+/* Spec says to try for 3 times, its doubled to add the software overhead */
+#define AUX_CH_WAKE_RETRY	6
+
+void intel_dp_wake_sink(struct intel_dp *intel_dp) {
+	u8 value = 0;
+	int ret = 0;
+
+	/*
+	 * Wake the sink device
+	 * Spec DP2.1 section 2.3.1.2 if AUX CH is powered down by writing 0x02
+	 * to DP_SET_POWER dpcd reg, 1ms time would be required to wake it up
+	 */
+	ret = poll_timeout_us(ret = drm_dp_dpcd_readb(&intel_dp->aux, DP_SET_POWER, &value),
+			      ret > 0,
+			      1000, AUX_CH_WAKE_RETRY * 1000, true);
+
+	/*
+	 * If sink is in D3 then it may not respond to the AUX tx so
+	 * wake it up to D3_AUX_ON state
+	 * If the above poll_timeout_us fails, try waking the sink.
+	 */
+	if (value == DP_SET_POWER_D3 || ret < 0) {
+		/* After setting to D0 need a min of 1ms to wake(Spec DP2.1 sec 2.3.1.2) */
+		drm_dp_dpcd_writeb(&intel_dp->aux, DP_SET_POWER,
+				   DP_SET_POWER_D0);
+		fsleep(1000);
+		drm_dp_dpcd_writeb(&intel_dp->aux, DP_SET_POWER,
+				   DP_SET_POWER_D3_AUX_ON);
+	}
+}
+
 static bool
 intel_edp_init_dpcd(struct intel_dp *intel_dp, struct intel_connector *connector)  { @@ -4713,6 +4745,8 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp, struct intel_connector *connector
 	/* this function is meant to be called only once */
 	drm_WARN_ON(display->drm, intel_dp->dpcd[DP_DPCD_REV] != 0);
 
+	intel_dp_wake_sink(intel_dp);
+
 	if (drm_dp_read_dpcd_caps(&intel_dp->aux, intel_dp->dpcd) != 0)
 		return false;
 
diff --git a/drivers/gpu/drm/i915/display/intel_dp.h b/drivers/gpu/drm/i915/display/intel_dp.h
index b0bbd5981f57..3f16077c0cc7 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.h
+++ b/drivers/gpu/drm/i915/display/intel_dp.h
@@ -232,6 +232,7 @@ bool intel_dp_dotclk_valid(struct intel_display *display,  bool intel_dp_joiner_candidate_valid(struct intel_connector *connector,
 				     int hdisplay,
 				     int num_joined_pipes);
+void intel_dp_wake_sink(struct intel_dp *intel_dp);
 
 #define for_each_joiner_candidate(__connector, __mode, __num_joined_pipes) \
 	for ((__num_joined_pipes) = 1; (__num_joined_pipes) <= (I915_MAX_PIPES); (__num_joined_pipes)++) \
--
2.25.1