On Thu, 2026-06-11 at 08:54 -0400, Stephen J. Fuhry wrote:
> 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]>
As intel_alpm.c is not supporting non-eDP ATM for now I think your fix
proposal is ok:
Reviewed-by: Jouni Högander <[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
