[PATCH] drm/i915/dp_mst: Work around Thunderbolt sink disconnect after SINK_COUNT_ESI read

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

Due to a problem in the iTBT DP-in adapter's firmware the sink on a TBT
link may get disconnected inadvertently if the SINK_COUNT_ESI and the
DP_LINK_SERVICE_IRQ_VECTOR_ESI0 registers are read in a single AUX
transaction. Work around the issue by reading these registers in
separate transactions.

The issue affects MTL+ platforms and will be fixed in the DP-in adapter
firmware, however releasing that firmware fix may take some time and is
not guaranteed to be available for all systems. Based on this apply the
workaround on affected platforms.

See HSD #13013007775.

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13760
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14147
Cc: stable@vger.kernel.org
Signed-off-by: Imre Deak <imre.deak@intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 21297bc4cc00d..208a953b04a2f 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -4538,6 +4538,23 @@ intel_dp_mst_disconnect(struct intel_dp *intel_dp)
 static bool
 intel_dp_get_sink_irq_esi(struct intel_dp *intel_dp, u8 *esi)
 {
+	struct intel_display *display = to_intel_display(intel_dp);
+
+	/*
+	 * Display WA for HSD #13013007775: mtl/arl/lnl
+	 * Read the sink count and link service IRQ registers in separate
+	 * transactions to prevent disconnecting the sink on a TBT link
+	 * inadvertently.
+	 */
+	if (IS_DISPLAY_VER(display, 14, 20) && !display->platform.battlemage) {
+		if (drm_dp_dpcd_read(&intel_dp->aux, DP_SINK_COUNT_ESI, esi, 3) != 3)
+			return false;
+
+		/* DP_SINK_COUNT_ESI + 3 == DP_LINK_SERVICE_IRQ_VECTOR_ESI0 */
+		return drm_dp_dpcd_readb(&intel_dp->aux, DP_LINK_SERVICE_IRQ_VECTOR_ESI0,
+					 &esi[3]) == 1;
+	}
+
 	return drm_dp_dpcd_read(&intel_dp->aux, DP_SINK_COUNT_ESI, esi, 4) == 4;
 }
 
-- 
2.44.2