patch "USB: usblp: don't call usb_set_interface if there's a single alt" added to usb-linus

This is a note to let you know that I've just added the patch titled

USB: usblp: don't call usb_set_interface if there's a single alt

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From d8c6edfa3f4ee0d45d7ce5ef18d1245b78774b9d Mon Sep 17 00:00:00 2001
From: Jeremy Figgins <[email protected]>
Date: Sat, 23 Jan 2021 18:21:36 -0600
Subject: USB: usblp: don't call usb_set_interface if there's a single alt

Some devices, such as the Winbond Electronics Corp. Virtual Com Port (Vendor=0416, ProdId=5011), lockup when usb_set_interface() or usb_clear_halt() are called. This device has only a single altsetting, so it should not be necessary to call usb_set_interface().

---
 drivers/usb/class/usblp.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

index 134dc2005ce9..c9f6e9758288 100644
@@ -1329,14 +1329,17 @@ static int usblp_set_protocol(struct usblp *usblp, int protocol)
 	if (protocol < USBLP_FIRST_PROTOCOL || protocol > USBLP_LAST_PROTOCOL)
 		return -EINVAL;
 
-	alts = usblp->protocol[protocol].alt_setting;
-	if (alts < 0)
-		return -EINVAL;
-	r = usb_set_interface(usblp->dev, usblp->ifnum, alts);
-	if (r < 0) {
-		printk(KERN_ERR "usblp: can't set desired altsetting %d on interface %d\n",
-			alts, usblp->ifnum);
-		return r;
+	/* Don't unnecessarily set the interface if there's a single alt. */
+	if (usblp->intf->num_altsetting > 1) {
+		alts = usblp->protocol[protocol].alt_setting;
+		if (alts < 0)
+			return -EINVAL;
+		r = usb_set_interface(usblp->dev, usblp->ifnum, alts);
+		if (r < 0) {
+			printk(KERN_ERR "usblp: can't set desired altsetting %d on interface %d\n",
+				alts, usblp->ifnum);
+			return r;
+		}
 	}
 
 	usblp->bidir = (usblp->protocol[protocol].epread != NULL);

2.30.0