[PATCH AUTOSEL 5.18 12/93] drm/amd/display: Detect dpcd_rev when hotplug mst monitor

Sasha Levin
2022-08-11T15:52:52Z

From: Wayne Lin <Wayne.Lin@amd.com>

[ Upstream commit 453b0016a054df0f442fda8a145b97a33816cab9 ]

[Why]
Once mst topology is constructed, later on new connected monitors
are reported to source by CSN message. Within CSN, there is no
carried info of DPCD_REV comparing to LINK_ADDRESS reply. As the
result, we might leave some ports connected to DP but without DPCD
revision number which will affect us determining the capability of
the DP Rx.

[How]
Send out remote DPCD read when the port's dpcd_rev is 0x0 in
detect_ctx(). Firstly, read out the value from DPCD 0x2200. If the
return value is 0x0, it's likely the DP1.2 DP Rx then we reques
revision from DPCD 0x0 again.

Reviewed-by: Hersen Wu <hersenwu@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
.../display/amdgpu_dm/amdgpu_dm_mst_types.c | 38 ++++++++++++++++++-
1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
index d864cae1af67..bcbb6f6f8c82 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
@@ -363,12 +363,48 @@ dm_dp_mst_detect(struct drm_connector *connector,
{
struct amdgpu_dm_connector *aconnector = to_amdgpu_dm_connector(connector);
struct amdgpu_dm_connector *master = aconnector->mst_port;
+ struct drm_dp_mst_port *port = aconnector->port;
+ int connection_status;

if (drm_connector_is_unregistered(connector))
return connector_status_disconnected;

- return drm_dp_mst_detect_port(connector, ctx, &master->mst_mgr,
+ connection_status = drm_dp_mst_detect_port(connector, ctx, &master->mst_mgr,
aconnector->port);
+
+ if (port->pdt != DP_PEER_DEVICE_NONE && !port->dpcd_rev) {
+ uint8_t dpcd_rev;
+ int ret;
+
+ ret = drm_dp_dpcd_readb(&port->aux, DP_DP13_DPCD_REV, &dpcd_rev);
+
+ if (ret == 1) {
+ port->dpcd_rev = dpcd_rev;
+
+ /* Could be DP1.2 DP Rx case*/
+ if (!dpcd_rev) {
+ ret = drm_dp_dpcd_readb(&port->aux, DP_DPCD_REV, &dpcd_rev);
+
+ if (ret == 1)
+ port->dpcd_rev = dpcd_rev;
+ }
+
+ if (!dpcd_rev)
+ DRM_DEBUG_KMS("Can't decide DPCD revision number!");
+ }
+
+ /*
+ * Could be legacy sink, logical port etc on DP1.2.
+ * Will get Nack under these cases when issue remote
+ * DPCD read.
+ */
+ if (ret != 1)
+ DRM_DEBUG_KMS("Can't access DPCD");
+ } else if (port->pdt == DP_PEER_DEVICE_NONE) {
+ port->dpcd_rev = 0;
+ }
+
+ return connection_status;
}

static int dm_dp_mst_atomic_check(struct drm_connector *connector,
--
2.35.1