On Thu, Jan 21, 2021 at 07:06:27PM -0600, Jeremy Figgins wrote: > On 1/21/21 5:02 PM, 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? > > > > 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? > > > > -- Pete > > > > > In my debugging, I found that it was the calls to usb_control_msg_send() in > both usb_set_interface() and usb_clear_halt() caused the printer to lockup. > I suppose another way to resolve this would to have a flag to prevent > usb_clear_halt()'s call to usb_control_msg_send(), but I'm not an expert in > USB, so I'm not sure of the ramifications of that. The simplest solution in all cases is just to avoid calling either usb_set_interface or usb_clear_halt. Especially since in cases where the interface has only one altsetting, neither call should be necessary. Alan Stern
