[PATCH v2] drm/i915/psr: clear the Panel Replay error status register

[Jake Steinman]

psr_get_status_and_error_status() selects the DPCD offset to read the error
status from based on whether Panel Replay is enabled:

	offset = intel_dp->psr.panel_replay_enabled ?
		 DP_PANEL_REPLAY_ERROR_STATUS : DP_PSR_ERROR_STATUS;

but intel_psr_short_pulse() acknowledges it unconditionally to the PSR
register. Under Panel Replay the error is therefore read from
DP_PANEL_REPLAY_ERROR_STATUS (0x2020) and the acknowledgement written to
DP_PSR_ERROR_STATUS (0x2006). DP_PANEL_REPLAY_ERROR_STATUS is never written
anywhere in the tree; it appears only in the read above and in its own #define.

The sink's Panel Replay error latch can consequently never be cleared. Once it
latches, every subsequent short pulse re-reads the same errors, so PSR is
disabled with sink_not_reliable set permanently, and until a short pulse
arrives the driver keeps Panel Replay enabled while the sink is reporting
errors it cannot see.

Observed on a Dell XPS 16 DA16260 (Panther Lake, Arc B390, display version
30.00) with the eDP Panel Replay quirk from commit cb8d155b0806 removed
locally so the feature could be exercised. The sink reports a persistently
latched error:

	Sink PANEL-REPLAY status: 0x2 [active, display from RFB]
	Sink PANEL-REPLAY error status: 0x1:
		PANEL-REPLAY Link CRC error

which survives across reads indefinitely, while dmesg stays silent and Panel
Replay Selective Update remains enabled.

Use the same conditional offset when clearing. psr->panel_replay_enabled
cannot be used at that point because intel_psr_disable_locked() clears it
earlier in the same function whenever an error was detected, which is exactly
the case that needs the Panel Replay offset, so save it beforehand.

v2: use a copy of panel_replay_enabled taken before
    intel_psr_disable_locked() clears it. In v1 the condition was evaluated
    after the disable, so it selected DP_PSR_ERROR_STATUS in the error path
    and the patch was a no-op there. Caught by Sashiko AI review.

Signed-off-by: Jake Steinman <j@xxxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/i915/display/intel_psr.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/i915/display/intel_psr.c
+++ b/drivers/gpu/drm/i915/display/intel_psr.c
@@ -3840,6 +3840,7 @@
 	struct intel_display *display = to_intel_display(intel_dp);
 	struct intel_psr *psr = &intel_dp->psr;
 	u8 status, error_status;
+	bool panel_replay_enabled;
 	const u8 errors = DP_PSR_RFB_STORAGE_ERROR |
 			  DP_PSR_VSC_SDP_UNCORRECTABLE_ERROR |
 			  DP_PSR_LINK_CRC_ERROR;
@@ -3860,6 +3861,12 @@
 		goto exit;
 	}
 
+	/*
+	 * Save this before intel_psr_disable_locked() clears it; the error
+	 * status is acknowledged to a different DPCD address depending on it.
+	 */
+	panel_replay_enabled = psr->panel_replay_enabled;
+
 	if ((!psr->panel_replay_enabled && status == DP_PSR_SINK_INTERNAL_ERROR) ||
 	    (error_status & errors)) {
 		intel_psr_disable_locked(intel_dp);
@@ -3885,7 +3892,10 @@
 			"PSR_ERROR_STATUS unhandled errors %x\n",
 			error_status & ~errors);
 	/* clear status register */
-	drm_dp_dpcd_writeb(&intel_dp->aux, DP_PSR_ERROR_STATUS, error_status);
+	drm_dp_dpcd_writeb(&intel_dp->aux,
+			   panel_replay_enabled ?
+			   DP_PANEL_REPLAY_ERROR_STATUS : DP_PSR_ERROR_STATUS,
+			   error_status);
 
 	if (!psr->panel_replay_enabled) {
 		psr_alpm_check(intel_dp);