[PATCH v2 20/21] drm/i915/dp: Read DPRX for all long HPD pulses

[Imre Deak <imre.deak@intel.com>]

The TBT DP tunnel BW request logic in the Thunderbolt Connection Manager
depends on the GFX driver reading out the sink's DPRX capabilities in
response to a long HPD pulse. Since in i915 this read-out can be blocked
by another connector's/encoder's hotplug event handling (which is
serialized by drm_mode_config::connection_mutex), do a dummy DPRX read-out
in the encoder's HPD pulse handler (which is not blocked by other
encoders).

Signed-off-by: Imre Deak <imre.deak@intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 35ef17439038a..f7f8bd5742ad4 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -6162,6 +6162,7 @@ intel_dp_hpd_pulse(struct intel_digital_port *dig_port, bool long_hpd)
 {
 	struct drm_i915_private *i915 = to_i915(dig_port->base.base.dev);
 	struct intel_dp *intel_dp = &dig_port->dp;
+	u8 dpcd[DP_RECEIVER_CAP_SIZE];
 
 	if (dig_port->base.type == INTEL_OUTPUT_EDP &&
 	    (long_hpd || !intel_pps_have_panel_power_or_vdd(intel_dp))) {
@@ -6184,6 +6185,17 @@ intel_dp_hpd_pulse(struct intel_digital_port *dig_port, bool long_hpd)
 		    dig_port->base.base.name,
 		    long_hpd ? "long" : "short");
 
+	/*
+	 * TBT DP tunnels require the GFX driver to read out the DPRX caps in
+	 * response to long HPD pulses. The DP hotplug handler does that,
+	 * however the hotplug handler may be blocked by another
+	 * connector's/encoder's hotplug handler. Since the TBT CM may not
+	 * 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)
+		intel_dp_read_dprx_caps(intel_dp, dpcd);
+
 	if (long_hpd) {
 		intel_dp->reset_link_params = true;
 		return IRQ_NONE;
-- 
2.39.2