linux-kernel - [PATCH v3 1/5] drm/bridge: it6505: fix link training state HW register reset

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Message-Id: <20250401-fix-link-training-v3-1-7f60f2ab7b8c@ite.com.tw>
Date: Tue, 01 Apr 2025 15:54:55 +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 v3 1/5] drm/bridge: it6505: fix link training state HW
 register reset

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

When connect to a DP-to-HDMI device which does not connect
to HDMI sink, it will report DPCD 00200h with SINK_COUNT = "0",
and issue HPD_IRQ when SINK_COUNT change to "1".

IT6505 can not recive HPD_IRQ before training done and driver will
force HW enter training done state when connect to such devices.

When HW is force to training done state and restart link training,
bits FORCE_RETRAIN and MANUAL_TRAIN at REG_TRAIN_CTRL1 must be set
at the same time to reset HW state.

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