linux-kernel - [PATCH v1 0/2] Revert commit 6ccb83d6c497 to fix DWC3 dual-role regression

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Message-ID: <20250522190912.457583-1-royluo@google.com>
Date: Thu, 22 May 2025 19:09:10 +0000
From: Roy Luo <royluo@...gle.com>
To: royluo@...gle.com, mathias.nyman@...el.com, quic_ugoswami@...cinc.com, 
	Thinh.Nguyen@...opsys.com, gregkh@...uxfoundation.org, michal.pecio@...il.com, 
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v1 0/2] Revert commit 6ccb83d6c497 to fix DWC3 dual-role regression

Commit 6ccb83d6c497 ("usb: xhci: Implement xhci_handshake_check_state()
helper") was introduced to workaround watchdog timeout issues on some
platforms, allowing xhci_reset() to bail out early without waiting
for the reset to complete.

This behavior causes a regression on SNPS DWC3 USB controller with
dual-role capability. When the DWC3 controller exits host mode and
removes xhci while a reset is still in progress, and then tries to
configure its hardware for device mode, the ongoing reset leads to
register access issues; specifically, all register reads returns 0.
These issues extend beyond the xhci register space (which is expected
during a reset) and affect the entire DWC3 IP block, causing the DWC3
device mode to malfunction.

To fix this regression without reintroducing the watchdog timeout issue,
the first patchset "usb: xhci: Skip xhci_reset in xhci_resume if
xhci is being removed" skips xhci_reset() in xhci_resume() reinit
path when xhci is being removed, which should address the watchdog
timeout issue. Then we can safely revert commit 6ccb83d6c497 ("usb:
xhci: Implement xhci_handshake_check_state() helper").

---
Changes in v1:
- Link to previous discussion: https://lore.kernel.org/r/20250517043942.372315-1-royluo@google.com/
---

Roy Luo (2):
  usb: xhci: Skip xhci_reset in xhci_resume if xhci is being removed
  Revert "usb: xhci: Implement xhci_handshake_check_state() helper"

 drivers/usb/host/xhci-ring.c |  5 ++---
 drivers/usb/host/xhci.c      | 31 +++++--------------------------
 drivers/usb/host/xhci.h      |  2 --
 3 files changed, 7 insertions(+), 31 deletions(-)

base-commit: 4a95bc121ccdaee04c4d72f84dbfa6b880a514b6
-- 
2.49.0.1204.g71687c7c1d-goog