linux-kernel - [PATCH v4 0/4] drm/bridge: it6505: fix DP link traning and improve compatibility

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Message-Id: <20250923-fix-link-training-v4-0-7c18f5d3891e@ite.com.tw>
Date: Tue, 23 Sep 2025 14:23:40 +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>, 
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
 Allen Chen <allen.chen@....com.tw>, Hermes Wu <hermes.wu@....com.tw>
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>, 
 Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Subject: [PATCH v4 0/4] drm/bridge: it6505: fix DP link traning and improve
 compatibility

IT6505 supports HW auto link training which will write DPCD and check
training status automatically. Some DP device can not pass
HW auto link training and must set link training step by step.

when HW auto link training fail, it may trigger video FIFO error,
and link training process will reset to beginning, and never try
step training method.

Modify training method improve compatibility to these DP devices.

Signed-off-by: Hermes Wu <Hermes.wu@....com.tw>
---
Changes in v4:
- squash patch 2/5 and 3/5, which do two different error check in same
  palce.
- edit commit message that warp at 70-77 boundary
- Link to v3: https://lore.kernel.org/r/20250401-fix-link-training-v3-0-7f60f2ab7b8c@ite.com.tw

Changes in v3:
- Patch 1/5 : add commit message for detial about changes
- Patch 2/5 : fix lost variable struct device *dev;
- Patch 3/5 : keep changes and remove refactoring
- Patch 5/5 : merge condition "it6505->step_train_only" check form if condiction into for loop.
- Link to v2: https://lore.kernel.org/r/20250326-fix-link-training-v2-0-756c8306f500@ite.com.tw

Changes in v2:
- 1. Split [PATCH 1/3] into 3 commits
- 2. Drop non necessary variable auto_ttrain_retry
- Link to v1: https://lore.kernel.org/all/20250318-fix-link-training-v1-0-19266711142c@ite.com.tw/

---
Hermes Wu (4):
      drm/bridge: it6505: fix link training state HW register reset
      drm/bridge: it6505: add INT status check  while link auto training
      drm/bridge: it6505: modify DP link training work
      drm/bridge: it6505: skip auto training when previous try fail

 drivers/gpu/drm/bridge/ite-it6505.c | 88 +++++++++++++++++++++----------------
 1 file changed, 50 insertions(+), 38 deletions(-)
---
base-commit: 938fbb16aba8f7b88e0fdcf56f315a5bbad41aad
change-id: 20250121-fix-link-training-461495494655

Best regards,
-- 
Hermes Wu <Hermes.wu@....com.tw>