On Fri, Feb 13, 2015 at 07:42:22PM -0600, Felipe Balbi wrote: > On Sat, Feb 14, 2015 at 08:13:36AM +0800, Greg KH wrote: > > On Fri, Feb 13, 2015 at 03:07:43PM -0600, Felipe Balbi wrote: > > > Every USB Host controller should use this new > > > macro to define for how long resume signalling > > > should be driven on the bus. > > > > > > Currently, almost every single USB controller > > > is using a 20ms timeout for resume signalling. > > > > > > That's problematic for two reasons: > > > > > > a) sometimes that 20ms timer expires a little > > > before 20ms, which makes us fail certification > > > > > > b) some (many) devices actually need more than > > > 20ms resume signalling. > > > > > > Sure, in case of (b) we can state that the device > > > is against the USB spec, but the fact is that > > > we have no control over which device the certification > > > lab will use. We also have no control over which host > > > they will use. Most likely they'll be using a Windows > > > PC which, again, we have no control over how that > > > USB stack is written and how long resume signalling > > > they are using. > > > > > > At the end of the day, we must make sure Linux passes > > > electrical compliance when working as Host or as Device > > > and currently we don't pass compliance as host because > > > we're driving resume signallig for exactly 20ms and > > > that confuses certification test setup resulting in > > > Certification failure. > > > > > > Signed-off-by: Felipe Balbi <ba...@ti.com> > > > --- > > > include/linux/usb.h | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/include/linux/usb.h b/include/linux/usb.h > > > index f89c24a03bd9..1dd89f0db344 100644 > > > --- a/include/linux/usb.h > > > +++ b/include/linux/usb.h > > > @@ -210,6 +210,9 @@ void usb_put_intf(struct usb_interface *intf); > > > #define USB_MAXINTERFACES 32 > > > #define USB_MAXIADS (USB_MAXINTERFACES/2) > > > > > > +/* USB Resume Timer */ > > > +#define USB_RESUME_TIMEOUT 40 /* ms */ > > > + > > > > If you add the comment as Alan suggested, feel free to add: > > > > Acked-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> > > Is this good enough ? > > commit 3154122f81c8411b432d5f44a196302243d5af3d > Author: Felipe Balbi <ba...@ti.com> > Date: Fri Feb 13 14:34:25 2015 -0600 > > usb: define a generic USB_RESUME_TIMEOUT macro > > Every USB Host controller should use this new > macro to define for how long resume signalling > should be driven on the bus. > > Currently, almost every single USB controller > is using a 20ms timeout for resume signalling. > > That's problematic for two reasons: > > a) sometimes that 20ms timer expires a little > before 20ms, which makes us fail certification > > b) some (many) devices actually need more than > 20ms resume signalling. > > Sure, in case of (b) we can state that the device > is against the USB spec, but the fact is that > we have no control over which device the certification > lab will use. We also have no control over which host > they will use. Most likely they'll be using a Windows > PC which, again, we have no control over how that > USB stack is written and how long resume signalling > they are using. > > At the end of the day, we must make sure Linux passes > electrical compliance when working as Host or as Device > and currently we don't pass compliance as host because > we're driving resume signallig for exactly 20ms and > that confuses certification test setup resulting in > Certification failure. > > Signed-off-by: Felipe Balbi <ba...@ti.com> > > diff --git a/include/linux/usb.h b/include/linux/usb.h > index 7ee1b5c3b4cb..447fe29b55b4 100644 > --- a/include/linux/usb.h > +++ b/include/linux/usb.h > @@ -205,6 +205,32 @@ void usb_put_intf(struct usb_interface *intf); > #define USB_MAXINTERFACES 32 > #define USB_MAXIADS (USB_MAXINTERFACES/2) > > +/* > + * USB Resume Timer: Every Host controller driver should drive the resume > + * signalling on the bus for the amount of time defined by this macro. > + * > + * That way we will have a 'stable' behavior among all HCDs supported by > Linux. > + * > + * Note that the USB Specification states we should drive resume for *at > least* > + * 20 ms, but it doesn't give an upper bound. This creates two possible > + * situations which we want to avoid: > + * > + * (a) sometimes an msleep(20) might expire slightly before 20 ms, which > causes > + * us to fail USB Electrical Tests, thus failing Certification > + * > + * (b) Some (many) devices actually need more than 20 ms of resume > signalling, > + * and while we can argue that's against the USB Specification, we don't have > + * control over which devices a certification laboratory will be using for > + * certification. If CertLab uses a device which was tested against Windows > and > + * that happens to have relaxed resume signalling rules, we might fall into > + * situations where we fail interoperability and electrical tests. > + * > + * In order to avoid both conditions, we're using a 40 ms resume timeout, > which > + * should cope with both LPJ calibration errors and devices not following > every > + * detail of the USB Specification. > + */ > +#define USB_RESUME_TIMEOUT 40 /* ms */ > + > /** > * struct usb_interface_cache - long-term representation of a device > interface > * @num_altsetting: number of altsettings defined. >
Looks great, thanks. Acked-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> Do we need these for -stable backports to make devices work properly with some host certification tests? If so, that's fine with me. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
