[PATCH] drm/dp_mst: Clear MSG_RDY flag before sending new message

[Wayne Lin <Wayne.Lin@amd.com>]

[Why & How]
The sequence for collecting down_reply/up_request from source
perspective should be:

Request_n->repeat (get partial reply of Request_n->clear message ready
flag to ack DPRX that the message is received) till all partial
replies for Request_n are received->new Request_n+1.

While assembling partial reply packets, reading out DPCD DOWN_REP
Sideband MSG buffer + clearing DOWN_REP_MSG_RDY flag should be
wrapped up as a complete operation for reading out a reply packet.
Kicking off a new request before clearing DOWN_REP_MSG_RDY flag might
be risky. e.g. If the reply of the new request has overwritten the
DPRX DOWN_REP Sideband MSG buffer before source writing ack to clear
DOWN_REP_MSG_RDY flag, source then unintentionally flushes the reply
for the new request. Should handle the up request in the same way.

In drm_dp_mst_hpd_irq(), we don't clear MSG_RDY flag before caliing
drm_dp_mst_kick_tx(). Fix that.

Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Cc: stable@vger.kernel.org
---
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c |  2 ++
 drivers/gpu/drm/display/drm_dp_mst_topology.c | 22 +++++++++++++++++++
 drivers/gpu/drm/i915/display/intel_dp.c       |  3 +++
 drivers/gpu/drm/nouveau/dispnv50/disp.c       |  2 ++
 4 files changed, 29 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 77277d90b6e2..5313a5656598 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -3166,6 +3166,8 @@ static void dm_handle_mst_sideband_msg(struct amdgpu_dm_connector *aconnector)
 			for (retry = 0; retry < 3; retry++) {
 				uint8_t wret;
 
+				/* MSG_RDY ack is done in drm*/
+				esi[1] &= ~(DP_DOWN_REP_MSG_RDY | DP_UP_REQ_MSG_RDY);
 				wret = drm_dp_dpcd_write(
 					&aconnector->dm_dp_aux.aux,
 					dpcd_addr + 1,
diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index 51a46689cda7..02aad713c67c 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -4054,6 +4054,9 @@ int drm_dp_mst_hpd_irq(struct drm_dp_mst_topology_mgr *mgr, u8 *esi, bool *handl
 {
 	int ret = 0;
 	int sc;
+	const int tosend = 1;
+	int retries = 0;
+	u8 buf = 0;
 	*handled = false;
 	sc = DP_GET_SINK_COUNT(esi[0]);
 
@@ -4072,6 +4075,25 @@ int drm_dp_mst_hpd_irq(struct drm_dp_mst_topology_mgr *mgr, u8 *esi, bool *handl
 		*handled = true;
 	}
 
+	if (*handled) {
+		buf = esi[1] & (DP_DOWN_REP_MSG_RDY | DP_UP_REQ_MSG_RDY);
+		do {
+			ret = drm_dp_dpcd_write(mgr->aux,
+						DP_DEVICE_SERVICE_IRQ_VECTOR_ESI0,
+						&buf,
+						tosend);
+
+			if (ret == tosend)
+				break;
+
+			retries++;
+		} while (retries < 5);
+
+		if (ret != tosend)
+			drm_dbg_kms(mgr->dev, "failed to write dpcd 0x%x\n",
+				    DP_DEVICE_SERVICE_IRQ_VECTOR_ESI0);
+	}
+
 	drm_dp_mst_kick_tx(mgr);
 	return ret;
 }
diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index bf80f296a8fd..abec3de38b66 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -3939,6 +3939,9 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
 		if (!memchr_inv(ack, 0, sizeof(ack)))
 			break;
 
+		/* MSG_RDY ack is done in drm*/
+		ack[1] &= ~(DP_DOWN_REP_MSG_RDY | DP_UP_REQ_MSG_RDY);
+
 		if (!intel_dp_ack_sink_irq_esi(intel_dp, ack))
 			drm_dbg_kms(&i915->drm, "Failed to ack ESI\n");
 	}
diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index edcb2529b402..e905987104ed 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -1336,6 +1336,8 @@ nv50_mstm_service(struct nouveau_drm *drm,
 		if (!handled)
 			break;
 
+		/* MSG_RDY ack is done in drm*/
+		esi[1] &= ~(DP_DOWN_REP_MSG_RDY | DP_UP_REQ_MSG_RDY);
 		rc = drm_dp_dpcd_write(aux, DP_SINK_COUNT_ESI + 1, &esi[1],
 				       3);
 		if (rc != 3) {
-- 
2.37.3