linux-kernel - [PATCH v2 1/5] drm/bridge: it6505: fix link training state HW register reset

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Message-Id: <20250326-fix-link-training-v2-1-756c8306f500@ite.com.tw>
Date: Wed, 26 Mar 2025 13:34:13 +0800
From: Hermes Wu via B4 Relay <devnull+Hermes.wu.ite.com.tw@...nel.org>
To: Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: Pet.Weng@....com.tw, Kenneth.Hung@....com.tw, treapking@...omium.org, 
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 Hermes Wu <Hermes.wu@....com.tw>
Subject: [PATCH v2 1/5] drm/bridge: it6505: fix link training state HW
 register reset

From: Hermes Wu <Hermes.wu@....com.tw>

In order to reset HW link auto training state,
bits FORCE_RETRAIN and MANUAL_TRAIN at REG_TRAIN_CTRL1 must be set
at the same time.

Signed-off-by: Hermes Wu <Hermes.wu@....com.tw>
---
 drivers/gpu/drm/bridge/ite-it6505.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ite-it6505.c b/drivers/gpu/drm/bridge/ite-it6505.c
index 88ef76a37fe6accacdd343839ff2569b31b18ceb..b47042dc06bb1e1dfd92bc0dc6d69dc918a140ba 100644
--- a/drivers/gpu/drm/bridge/ite-it6505.c
+++ b/drivers/gpu/drm/bridge/ite-it6505.c
@@ -1806,7 +1806,9 @@ static bool it6505_link_start_auto_train(struct it6505 *it6505)
 	mutex_lock(&it6505->aux_lock);
 	it6505_set_bits(it6505, REG_TRAIN_CTRL0,
 			FORCE_CR_DONE | FORCE_EQ_DONE, 0x00);
-	it6505_write(it6505, REG_TRAIN_CTRL1, FORCE_RETRAIN);
+	/* reset link state machine and re start training*/
+	it6505_write(it6505, REG_TRAIN_CTRL1,
+		     FORCE_RETRAIN | MANUAL_TRAIN);
 	it6505_write(it6505, REG_TRAIN_CTRL1, AUTO_TRAIN);
 
 	while (timeout > 0) {
@@ -2377,7 +2379,7 @@ static void it6505_stop_link_train(struct it6505 *it6505)
 {
 	it6505->link_state = LINK_IDLE;
 	cancel_work_sync(&it6505->link_works);
-	it6505_write(it6505, REG_TRAIN_CTRL1, FORCE_RETRAIN);
+	it6505_write(it6505, REG_TRAIN_CTRL1, FORCE_RETRAIN | MANUAL_TRAIN);
 }
 
 static void it6505_link_train_ok(struct it6505 *it6505)

-- 
2.34.1