Re: [ISSUE REPORT] xHCI infinite endpoint reset loop on full-speed after transfer error

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, May 12, 2025 at 02:39:13PM +0800, Guan Wang wrote:
> From: Guan Wang <guan.wang.jy@gmail.com>
> 
> Hello,
> 
> Using Linux version 6.15.0-rc5-00032, I encountered an issue where the xHCI controller enters an
> infinite loop while attempting to recover a USB endpoint. This causes the xHCI driver to get stuck,
> and no USB transfers can proceed.
> 
> This issue appears to only occur with full-speed bulk devices such as USB serial adapters(e.g.,
> USB-Serial or CDC-ACM class). I've reproduced it using CH340 and CP2102 USB serial devices.
> 
> **Steps to reproduce:**
> 1. Attach the device.
> 2. Start continuous data transfer (e.g., `cat /dev/ttyUSB0`).
> 3. Induce transfer errors via:
>    - EMI interference
>    - Sudden temperature changes
>    - Long USB cables
>    - Briefly shorting DP/DM lines to simulate a transaction error
> 
> After this, the xHCI controller enters an infinite reset loop on the affected endpoint. "Transfer error"
> messages continuously appear in the logs, creating a log storm. The issue seems to improve or disappear
> when an external high-speed USB hub is inserted between the host and device.
> 
> Do you have any comments or suggestions? The log is shown below:
> 
> 
> **USB emulation dmesg**
> 
> [   41.109377] usb 3-1: new full-speed USB device number 2 using xhci-renesas-hcd
> [   41.277651] xhci-renesas-hcd ee000000.usb: add ep 0x82, slot id 1, new drop flags = 0x0, new add flags = 0x21
> [   41.277676] xhci-renesas-hcd ee000000.usb: add ep 0x2, slot id 1, new drop flags = 0x0, new add flags = 0x31
> [   41.277697] xhci-renesas-hcd ee000000.usb: add ep 0x81, slot id 1, new drop flags = 0x0, new add flags = 0x39

Does this happen on other xhci controllers as well?  Or just the Renesas
chip?

thanks,

greg k-h