Re: [PATCH] USB: cdc-acm: start bulk-IN polling when ALWAYS_POLL_CTRL is set

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, May 14, 2026 at 03:42:52PM -0400, Dave Carey wrote:
> The INGENIC 17EF:6161 touchscreen composite device has a ~55-second
> watchdog that resets the USB device if the bulk-IN endpoint on the CDC
> data interface goes unread. The existing ALWAYS_POLL_CTRL quirk keeps
> the notification endpoint (ctrlurb / EP 0x82) polling continuously, but
> that alone is insufficient: the firmware monitors bulk-IN activity, not
> just notification-endpoint activity.
> 
> Add acm_submit_read_urbs() calls to the two ALWAYS_POLL_CTRL paths that
> already restart the ctrlurb:
> 
> 1. acm_probe(): start bulk reads at probe time alongside the ctrlurb,
> so the watchdog is satisfied from first bind without requiring a
> userspace process to open /dev/ttyACMn.
> 
> 2. acm_port_shutdown(): restart bulk reads after port close alongside
> the ctrlurb restart, so the watchdog keeps running when the last
> TTY user closes the port.
> 
> acm_read_bulk_callback() already resubmits each URB unconditionally on
> normal completion, so once submitted the reads remain active until an
> explicit kill (disconnect, suspend). acm_submit_read_urb() is a no-op
> for URBs that are already in flight (read_urbs_free bit clear), so the
> existing acm_port_activate() call remains correct and races are avoided.
> 
> Tested on Lenovo Yoga Book 9 14IAH10 (83KJ): without this patch the
> device resets every ~55 s when no TTY is open; with it the device
> remains stable indefinitely.
> 
> Signed-off-by: Dave Carey <carvsdriver@gmail.com>
> Tested-by: Dave Carey <carvsdriver@gmail.com>
> ---
> This follows commit f58752ebcb35 ("USB: CDC-ACM: add INGENIC 17EF:6161
> quirk for Yoga Book 9 14IAH10"), which added ALWAYS_POLL_CTRL to keep
> the ctrlurb active. That commit addressed the notification-endpoint
> watchdog (~20 s). This patch addresses a second watchdog that fires
> when bulk-IN data goes unread for ~55 s.
> 
> This patch is based on top of Wentao Guan's pending fix
> ("USB: cdc-acm: fix misplaced quirk defines and BIT(9) collision") which
> moves VENDOR_CLASS_DATA_IFACE and ALWAYS_POLL_CTRL from inside
> acm_ctrl_msg() to cdc-acm.h and reassigns them to BIT(10)/BIT(11) to
> avoid the NO_UNION_12 collision. The bulk-IN additions here are
> independent of that renumbering and apply cleanly to either base, but
> the combined tree is the correct target once Wentao's fix merges.
> 
> drivers/usb/class/cdc-acm.c | 6 ++++++
> 1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
> --- a/drivers/usb/class/cdc-acm.c
> +++ b/drivers/usb/class/cdc-acm.c
> @@ -799,6 +799,9 @@
> "ctrl polling restart failed after port close\n");
> /* port_shutdown() cleared DTR/RTS; restore them */
> acm_set_control(acm, USB_CDC_CTRL_DTR | USB_CDC_CTRL_RTS);
> + if (acm_submit_read_urbs(acm, GFP_KERNEL))
> + dev_dbg(&acm->control->dev,
> + "read urb restart failed after port close\n");
> }
> }
> 
> @@ -1566,6 +1569,9 @@
> if (usb_submit_urb(acm->ctrlurb, GFP_KERNEL))
> dev_warn(&intf->dev,
> "failed to start persistent ctrl polling\n");
> + if (acm_submit_read_urbs(acm, GFP_KERNEL))
> + dev_warn(&intf->dev,
> + "failed to start persistent bulk read polling\n");
> }
> 
> return 0;
> --
> 2.47.0

Hi,

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