[PATCH AUTOSEL 6.18-6.1] USB: cdc-acm: start bulk-IN polling when ALWAYS_POLL_CTRL is set

[Sasha Levin]

From: Dave Carey <carvsdriver@xxxxxxxxx>

[ Upstream commit e5ab27ddd74e2d67a94c51c6f2ad87b1ff13912b ]

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@xxxxxxxxx>
Link: https://patch.msgid.link/20260515141940.751397-1-carvsdriver@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---

LLM Generated explanations, may be completely bogus:

The background searches finished and match the earlier analysis:

- **`git log --grep="start bulk-IN polling"` /
  `--grep="ALWAYS_POLL_CTRL"`** only turned up the prerequisite Yoga
  Book quirk commits (`5d29d7ff8679e`, `625153b917bc4`), not the bulk-IN
  polling fix.
- **`git log --grep="bulk-IN polling"` / `--grep="start bulk"`** found
  no matching fix commit in this tree.

So the patch under review is **not present in 6.18.44**; the incomplete
`ALWAYS_POLL_CTRL` behavior is still there. The backport recommendation
remains **YES** — it completes the quirk already in this tree.

 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
index 12f9fe62199ba..d6a2f1591460a 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -797,6 +797,9 @@ static void acm_port_shutdown(struct tty_port *port)
 				"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");
 	}
 }
 
@@ -1564,6 +1567,9 @@ static int acm_probe(struct usb_interface *intf,
 		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;
-- 
2.53.0