Hi Mathias, Roy,
On Thu, May 22, 2025, Roy Luo wrote:
xhci_reset() currently returns -ENODEV if XHCI_STATE_REMOVING is set, without completing the xhci handshake, unless the reset completes exceptionally quickly. This behavior causes a regression on Synopsys DWC3 USB controllers with dual-role capabilities.
Specifically, when a DWC3 controller exits host mode and removes xhci while a reset is still in progress, and then attempts to configure its hardware for device mode, the ongoing, incomplete reset leads to critical register access issues. All register reads return zero, not just within the xHCI register space (which might be expected during a reset), but across the entire DWC3 IP block.
This patch addresses the issue by preventing xhci_reset() from being called in xhci_resume() and bailing out early in the reinit flow when XHCI_STATE_REMOVING is set.
Cc: stable@vger.kernel.org Fixes: 6ccb83d6c497 ("usb: xhci: Implement xhci_handshake_check_state() helper") Suggested-by: Mathias Nyman mathias.nyman@intel.com Signed-off-by: Roy Luo royluo@google.com
drivers/usb/host/xhci.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c index 90eb491267b5..244b12eafd95 100644 --- a/drivers/usb/host/xhci.c +++ b/drivers/usb/host/xhci.c @@ -1084,7 +1084,10 @@ int xhci_resume(struct xhci_hcd *xhci, bool power_lost, bool is_auto_resume) xhci_dbg(xhci, "Stop HCD\n"); xhci_halt(xhci); xhci_zero_64b_regs(xhci);
retval = xhci_reset(xhci, XHCI_RESET_LONG_USEC);
if (xhci->xhc_state & XHCI_STATE_REMOVING)retval = -ENODEV;elseretval = xhci_reset(xhci, XHCI_RESET_LONG_USEC);
How can this prevent the xhc_state from changing while in reset? There's no locking in xhci-plat.
I would suggest to simply revert the commit 6ccb83d6c497 that causes regression first. We can investigate and look into a solution to the specific Qcom issue afterward.
Note that this commit may impact role-switching flow for all DRD dwc3 (and perhaps others), which may also impact other Qcom DRD platforms.
Thanks, Thinh
spin_unlock_irq(&xhci->lock); if (retval) return retval;-- 2.49.0.1204.g71687c7c1d-goog