On Thu, Jan 21, 2021 at 05:02:49PM -0600, Pete Zaitcev wrote: > On Thu, 21 Jan 2021 14:29:29 -0500 > Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > > I'm also concerned about regressions. This is a legacy class driver, > > > only used where CUPS is not applicable, mostly with truly ancient > > > devices. So yes, setting a zero altsetting after enumeration should > > > be unnecessary. But you never know with the old firmware. > > > How about skipping the call whenever the interface has only one > > altsetting? > > Do you mean when it's only one and not equal to zero? If there's only one, it _has_ to be equal to 0. According to section 9.2.3 of the USB-2 spec: Alternate settings range from zero to one less than the number of alternate settings for a specific interface. > BTW, one other thing bothers me. Jeremy confirmed that my patch > worked, which skips the call when USB_QUIRK_NO_SET_INTF is set. > But if we look into drivers/usb/core/message.c, the control > exchange to set the altsetting is skipped in that case anyway. > So, usblp was calling usb_set_protocol, the suspect control was > skipped, but something else caused a problem. Could it be the > attempt to clear halt that triggered the problem? It could very well be. The printer might not reset the endpoint toggle when it gets the Clear-Halt request. It's also possible that when the quirk flag wasn't set (so the Set-Interface request was issued), the printer failed reset the endpoint toggle. Alan Stern
