[PATCH v4] drm/i915/display/lspcon: Increase LSPCON mode settle timeout

[Niko Tsirakis]

This is to eliminate all cases of "*ERROR* LSPCON mode hasn't settled",
followed by link training errors. Intel engineers recommended increasing
this timeout and that does resolve the issue.

On some CometLake-based device designs the Parade PS175 takes more than
400ms to settle in PCON mode. 100 reboot trials on one device resulted
in a median settle time of 440ms and a maximum of 444ms. Even after
increasing the timeout to 500ms, 2% of devices still had this error. So
this increases the timeout to 800ms.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/9443
Signed-off-by: Pablo Ceballos <pceballos at google.com>
Signed-off-by: Niko Tsirakis <ntsirakis at google.com>
---
 drivers/gpu/drm/i915/display/intel_lspcon.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_lspcon.c b/drivers/gpu/drm/i915/display/intel_lspcon.c
index dc1b35559afd..92536482e657 100644
--- a/drivers/gpu/drm/i915/display/intel_lspcon.c
+++ b/drivers/gpu/drm/i915/display/intel_lspcon.c
@@ -116,6 +116,18 @@ static enum drm_lspcon_mode lspcon_get_current_mode(struct intel_lspcon *lspcon)
 	return current_mode;
 }
 
+static int lspcon_get_mode_settle_timeout(struct intel_lspcon *lspcon)
+{
+	/*
+	 * On some CometLake-based device designs the Parade PS175 takes more
+	 * than 400ms to settle in PCON mode. 100 reboot trials on one device
+	 * resulted in a median settle time of 440ms and a maximum of 444ms.
+	 * Even after increasing the timeout to 500ms, 2% of devices still had
+	 * this error. So this sets the timeout to 800ms.
+	 */
+	return lspcon->vendor == LSPCON_VENDOR_PARADE ? 800 : 400;
+}
+
 static enum drm_lspcon_mode lspcon_wait_mode(struct intel_lspcon *lspcon,
 					     enum drm_lspcon_mode mode)
 {
@@ -128,7 +140,8 @@ static enum drm_lspcon_mode lspcon_wait_mode(struct intel_lspcon *lspcon,
 	DRM_DEBUG_KMS("Waiting for LSPCON mode %s to settle\n",
 		      lspcon_mode_name(mode));
 
-	wait_for((current_mode = lspcon_get_current_mode(lspcon)) == mode, 400);
+	wait_for((current_mode = lspcon_get_current_mode(lspcon)) == mode,
+		lspcon_get_mode_settle_timeout(lspcon));
 	if (current_mode != mode)
 		DRM_ERROR("LSPCON mode hasn't settled\n");
 
-- 
2.42.0.582.g8ccd20d70d-goog