drm/i915/dp_link_caps: Re-enable link configurations after sink caps change

Re-enable link configurations after sink capabilities change or the link
got reset before updating the link capabilities (due to an RX_CAP_CHANGED
HPD IRQ for the currently connected sink, or a new sink getting
connected).

This makes resetting the link explicitly by calling
intel_dp_link_caps_reset() subsequently redundant; keep the existing
behavior wrt. this for now, adding only a TODO: to remove the explicit
reset.

While at it add documentation for intel_dp_link_caps_update().

Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260701153204.4124150-10-imre.deak@intel.com

3 files changed, 43 insertions, 5 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 64090a106847..6e855131d1de 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -701,7 +701,8 @@ static bool intel_dp_set_common_link_params(struct intel_dp *intel_dp)
 	intel_dp_get_common_rates(intel_dp, common_rates, &num_common_rates);
 	if (intel_dp_link_caps_update(intel_dp->link.caps,
 				      common_rates, num_common_rates,
-				      intel_dp_get_max_common_lane_count(intel_dp)))
+				      intel_dp_get_max_common_lane_count(intel_dp),
+				      intel_dp->reset_link_params))
 		params_changed = true;
 
 	return params_changed;
@@ -3613,6 +3614,11 @@ void intel_dp_set_link_params(struct intel_dp *intel_dp,
 
 void intel_dp_reset_link_params(struct intel_dp *intel_dp)
 {
+	/*
+	 * TODO: Remove the following reset of link capabilities, as
+	 * this isn't needed after intel_dp_link_caps_update(reset=true)
+	 * was called.
+	 */
 	intel_dp_link_caps_reset(intel_dp->link.caps);
 	intel_dp->link.mst_probed_lane_count = 0;
 	intel_dp->link.mst_probed_rate = 0;
diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_caps.c b/drivers/gpu/drm/i915/display/intel_dp_link_caps.c
index 667d2e55cea1..de520bd423d5 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_caps.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_caps.c
@@ -709,14 +709,42 @@ static int link_config_cmp_by_lane_rate(const void *a, const void *b, const void
 	return lce_a->link_rate_idx - lce_b->link_rate_idx;
 }
 
-/* Return %true if the supported link parameters have changed. */
+/**
+ * intel_dp_link_caps_update - rebuild the supported link configuration state
+ * @link_caps: link capabilities state
+ * @rates: supported common link rates
+ * @num_rates: number of entries in @rates
+ * @max_lane_count: supported maximum lane count
+ * @reset: reset limits and disabled configs
+ *
+ * Rebuild the supported link configuration state from @rates and
+ * @max_lane_count.
+ *
+ * If @reset is %true, reset the maximum link limits to the maximum
+ * supported rate and lane count, and re-enable all configurations.
+ *
+ * This function is called regularly, at least after a sink is connected,
+ * but it may also be called later whenever the sink capabilities may have
+ * changed, for example in response to HPD IRQ / RX_CAP_CHANGED signaling.
+ *
+ * In the Intel driver this function is currently called whenever the
+ * connector detect handler runs, after reading the sink capabilities. This
+ * may change if those capabilities are cached until the sink is
+ * disconnected, or until RX_CAP_CHANGED is signaled. In any case, this
+ * function should be called whenever the sink capabilities were read out
+ * and may have changed.
+ *
+ * Returns:
+ * - %true if the link capabilities have changed, %false otherwise.
+ */
 bool intel_dp_link_caps_update(struct intel_dp_link_caps *link_caps,
-			       const int *rates, int num_rates, int max_lane_count)
+			       const int *rates, int num_rates, int max_lane_count,
+			       bool reset)
 {
 	struct intel_dp *intel_dp = link_caps->dp;
 	struct intel_display *display = to_intel_display(intel_dp);
 	struct intel_dp_link_config_entry *lce;
-	bool link_params_changed = false;
+	bool link_params_changed = reset;
 	int num_common_lane_configs;
 	int i;
 	int j;
@@ -778,6 +806,9 @@ bool intel_dp_link_caps_update(struct intel_dp_link_caps *link_caps,
 	       link_config_cmp_by_lane_rate, NULL,
 	       link_caps);
 
+	if (link_params_changed)
+		reset_max_link_limits_reenable_all(link_caps);
+
 	return link_params_changed;
 }
 
diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_caps.h b/drivers/gpu/drm/i915/display/intel_dp_link_caps.h
index 79aca74ad9ee..dcbde890809b 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_caps.h
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_caps.h
@@ -147,7 +147,8 @@ bool intel_dp_link_caps_set_max_limits(struct intel_dp_link_caps *link_caps,
 void intel_dp_link_caps_reset_max_limits(struct intel_dp_link_caps *link_caps);
 
 bool intel_dp_link_caps_update(struct intel_dp_link_caps *link_caps,
-			       const int *rates, int num_rates, int max_lane_count);
+			       const int *rates, int num_rates, int max_lane_count,
+			       bool reset);
 void intel_dp_link_caps_reset(struct intel_dp_link_caps *link_caps);
 
 void intel_dp_link_caps_debugfs_add(struct intel_connector *connector);