On Sat, Jan 23, 2021 at 12:46:06PM -0600, Jeremy Figgins wrote: > On 1/22/21 10:22 AM, Alan Stern wrote: > > 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 > > > > I can confirm that only calling usb_clear_halt() if USB_QUIRK_NO_SET_INTF is > not set (and setting it for my device) does allow my device to work. What is > the next step? Should I submit a v2 patch? Why don't you write, test, and submit a patch that will make usblp avoid calling usb_set_interface and usb_clear_halt when there's only one altsetting? Alan Stern
