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

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, May 15, 2026 at 09:04:32AM -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>

It's implied when you sign off that you had tested, so no need to have
the tested-by.