intel_alpm_get_error() unconditionally reads DP_RECEIVER_ALPM_STATUS via
AUX from any DP connection that receives a short-pulse interrupt. However,
alpm_dpcd is only populated by intel_edp_init_dpcd(), so it is zero for
all external (non-eDP) DP and DP-MST connections. On such connections the
AUX read fails, producing a spurious
[drm] *ERROR* Error reading ALPM status
and setting sink_alpm_error = true, which is then visible in the ALPM
debug output even on hardware that never enabled ALPM.
intel_alpm_disable() already has the same guard (DISPLAY_VER check plus
!intel_dp->alpm_dpcd); extend the same logic to intel_alpm_get_error() so
it returns early without attempting the AUX transaction when ALPM is not
supported by the sink.
Reproducer: ThinkPad T14 Gen1 (Alder Lake-P / i915 DISPLAY_VER 12) docked
via Lenovo ThinkPad USB-C Dock Gen2 with external DP-MST monitors. On
every DPMS wake the error fires once on the dock's upstream DP port.
Fixes: 2063174c22da ("drm/i915/lobf: Check for sink error and disable LOBF")
Signed-off-by: Stephen J. Fuhry <[email protected]>
---
drivers/gpu/drm/i915/display/intel_alpm.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/gpu/drm/i915/display/intel_alpm.c
b/drivers/gpu/drm/i915/display/intel_alpm.c
index a7350ce8e716..4bb0c00741c4 100644
--- a/drivers/gpu/drm/i915/display/intel_alpm.c
+++ b/drivers/gpu/drm/i915/display/intel_alpm.c
@@ -611,6 +611,9 @@ bool intel_alpm_get_error(struct intel_dp *intel_dp)
u8 val;
int r;
+ if (!intel_dp->alpm_dpcd)
+ return false;
+
r = drm_dp_dpcd_readb(aux, DP_RECEIVER_ALPM_STATUS, &val);
if (r != 1) {
drm_err(display->drm, "Error reading ALPM status\n");
--
2.39.5
