On 1/18/21 10:43 AM, Michael Sweet wrote:
FWIW, the CUPS libusb-based backend only sets the alt setting if there is more than 1 alt setting in the descriptor.
On Jan 18, 2021, at 11:31 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
On Sun, Jan 17, 2021 at 11:44:16PM -0600, Pete Zaitcev wrote:
On Sun, 17 Jan 2021 15:36:39 -0600
Jeremy Figgins <kernel@xxxxxxxxxxxxxxxxx> wrote:
The naming is designed to mirror the existing
USB_QUIRK_NO_SET_INTF flag, but that flag is
not sufficient to make these devices work.
+ { 0x0416, 0x5011, USBLP_QUIRK_NO_SET_INTF }, /* Winbond Electronics Corp. Virtual Com Port */
Jeremy, thanks for the patch. It looks mostly fine code-wise (quirk is
out of numerical order), but I have a question: did you consider keying
off usblp->dev->quirks instead?
How about this:
diff --git a/drivers/usb/class/usblp.c b/drivers/usb/class/usblp.c
index 37062130a03c..0c4a98f00797 100644
--- a/drivers/usb/class/usblp.c
+++ b/drivers/usb/class/usblp.c
@@ -1315,7 +1315,11 @@ static int usblp_set_protocol(struct usblp *usblp, int protocol)
alts = usblp->protocol[protocol].alt_setting;
if (alts < 0)
return -EINVAL;
- r = usb_set_interface(usblp->dev, usblp->ifnum, alts);
+ if (usblp->dev->quirks & USB_QUIRK_NO_SET_INTF) {
+ r = 0;
+ } else {
+ 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);
Would it be practical simply to skip the usb_set_interface() call
whenever alts is 0? After all, devices use altsetting 0 by default; it
shouldn't be necessary to tell them to do so.
Alan Stern
________________________
Michael Sweet
>
Pete, your proposed change does work. I created USBLP_QUIRK_NO_SET_INTF
because I was concerned about overloading the meaning of
USB_QUIRK_NO_SET_INTF, but if you think that's the better approach, I'm
happy to resubmit the patch.
Alan, just to confirm, alts=0 for this device.
Jeremy Figgins
