Re: autosuspend for hid

Am Mittwoch, 16. Mai 2007 17:20 schrieb Alan Stern:
> > @@ -592,8 +604,21 @@ static int hid_get_class_descriptor(stru
> >  int usbhid_open(struct hid_device *hid)
> >  {
> >       struct usbhid_device *usbhid = hid->driver_data;
> > +     int res;
> >  
> > -     hid->open++;
> > +     mutex_lock(&hid_open_mut);
> > +     if (!hid->open++) {
> > +             res = usb_autopm_get_interface(usbhid->intf);
> > +             /* the device must be awake to reliable request remote wakeup */
> > +             if (res < 0) {
> > +                     hid->open--;
> > +                     mutex_unlock(&hid_open_mut);
> > +                     return -EIO;
> > +             }
> > +             usbhid->intf->needs_remote_wakeup = 1;
> > +             usb_autopm_put_interface(usbhid->intf);
> > +     }
> > +     mutex_unlock(&hid_open_mut);
> >       if (hid_start_in(hid))
> >               hid_io_error(hid);
> >       return 0;
> 
> Don't you need to do usb_autopm_get_interface() before hid_start_in()?

hid_start_in() takes the spinlock and checks for a suspension. In the
unlikely case that the device already has been suspended, remote
wakeup must be active and resume() will call hid_start_in() again.

> > @@ -1154,13 +1184,26 @@ static int hid_suspend(struct usb_interf
> >       struct usbhid_device *usbhid = hid->driver_data;
> >       struct usb_device *udev = interface_to_usbdev(intf);
> >  
> > -
> > -     spin_lock_irq(&usbhid->inlock);
> > -     set_bit(HID_REPORTED_IDLE, &usbhid->iofl);
> > -     spin_unlock_irq(&usbhid->inlock);
> > -     if (usbhid_wait_io(hid) < 0)
> > -             return -EIO;
> > -
> > +     if (udev->auto_pm) {
> > +             spin_lock_irq(&usbhid->inlock); /* Sync with error handler */
> > +             if (!test_bit(HID_RESET_PENDING, &usbhid->iofl)
> > +                 && !test_bit(HID_CLEAR_HALT, &usbhid->iofl)
> > +                 && !test_bit(HID_OUT_RUNNING, &usbhid->iofl)
> > +                 && !test_bit(HID_CTRL_RUNNING, &usbhid->iofl))
> > +             {
> > +                     set_bit(HID_REPORTED_IDLE, &usbhid->iofl);
> > +                     spin_unlock_irq(&usbhid->inlock);
> > +             } else {
> > +                     spin_unlock_irq(&usbhid->inlock);
> > +                     return -EBUSY;
> > +             }
> > +     } else {
> > +             spin_lock_irq(&usbhid->inlock);
> > +             set_bit(HID_REPORTED_IDLE, &usbhid->iofl);
> > +             spin_unlock_irq(&usbhid->inlock);
> > +             if (usbhid_wait_io(hid) < 0)
> > +                     return -EIO;
> > +     }
> >       del_timer(&usbhid->io_retry);
> >       usb_kill_urb(usbhid->urbin);
> >       flush_scheduled_work();
> 
> This might be simpler if you inverted the order of the tests.  That is, 
> first get the spinlock, then test for
> 
>         udev->auto_pm && (test_bit() || test_bit() || ...)

But that would put code needlessly under lock.
> 
> to see if you need to fail right away.  You probably don't even need to
> check udev->auto_pm again before calling usbhid_wait_io.
> 
> > @@ -1175,6 +1218,7 @@ static int hid_resume(struct usb_interfa
> >       int status;
> >  
> >       clear_bit(HID_REPORTED_IDLE, &usbhid->iofl);
> > +     usbhid_mark_busy(usbhid);
> >       usbhid->retry_delay = 0;
> >       status = hid_start_in(hid);
> >       usbhid_restart_queues(usbhid);
> 
> Again, don't you need to call usb_autopm_get_interface() before 
> hid_start_in()?

resume() and suspend() have mutual exclusion, don't they? So
the device must be awake while resume() is running.

> One last thing, about the race between a last-minute URB completion and 
> autosuspend.  The USB autosuspend core routine doesn't check the 
> last_busy value after suspending the interface drivers and before 
> suspending the device.  Do we need to?

As the lock is per device, the resume() call would wait and proceed
immediately after suspend() drops the lock. I see no problem.

	Regards
		Oliver
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