linux-kernel - [PATCH v3] drm/i915/display/lspcon: Increase LSPCON mode settle timeout

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Date:   Wed, 16 Aug 2023 04:56:54 +0000
From:   Pablo Ceballos <pceballos@...gle.com>
To:     Ankit K Nautiyal <ankit.k.nautiyal@...el.com>
Cc:     David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        "Ville Syrjälä" 
        <ville.syrjala@...ux.intel.com>,
        Pablo Ceballos <pceballos@...gle.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3] drm/i915/display/lspcon: Increase LSPCON mode settle timeout

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.

Signed-off-by: Pablo Ceballos <pceballos@...gle.com>
---

V2: Added more details in the commit message
V3: Only apply the increased timeout if the vendor is Parade

drivers/gpu/drm/i915/display/intel_lspcon.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_lspcon.c b/drivers/gpu/drm/i915/display/intel_lspcon.c
index bb3b5355a0d9..b07eab84cc63 100644
--- a/drivers/gpu/drm/i915/display/intel_lspcon.c
+++ b/drivers/gpu/drm/i915/display/intel_lspcon.c
@@ -153,6 +153,24 @@ static enum drm_lspcon_mode lspcon_get_current_mode(struct intel_lspcon *lspcon)
 	return current_mode;
 }
 
+static u32 lspcon_get_mode_settle_timeout(struct intel_lspcon *lspcon)
+{
+	u32 timeout_ms = 400;
+
+	/*
+	 * 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.
+	 */
+	if (lspcon->vendor == LSPCON_VENDOR_PARADE)
+		timeout_ms = 800;
+
+	return timeout_ms;
+}
+
+
 static enum drm_lspcon_mode lspcon_wait_mode(struct intel_lspcon *lspcon,
 					     enum drm_lspcon_mode mode)
 {
@@ -167,7 +185,8 @@ static enum drm_lspcon_mode lspcon_wait_mode(struct intel_lspcon *lspcon,
 	drm_dbg_kms(&i915->drm, "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_err(&i915->drm, "LSPCON mode hasn't settled\n");
 
-- 
2.39.2