Re: [PATCH 01/13] usb: define a generic USB_RESUME_TIMEOUT macro

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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 <balbi@xxxxxx>
> > > ---
> > >  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 <gregkh@xxxxxxxxxxxxxxxxxxx>
> 
> Is this good enough ?
> 
> commit 3154122f81c8411b432d5f44a196302243d5af3d
> Author: Felipe Balbi <balbi@xxxxxx>
> 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 <balbi@xxxxxx>
> 
> 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 */
> +

It should be ok for chipidea core which end of its resume signal
automatically about ~21ms.

By the way, which item you have failed for USB Certification test?

Acked-by: Peter Chen <peter.chen@xxxxxxxxxxxxx>

-- 

Best Regards,
Peter Chen
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