Re: [PATCH v2] usb: core: reduce power-on-good delay time of root hub

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Nov 03, 2021 at 10:37:33PM +0200, Mathias Nyman wrote:
> On 2.11.2021 22.29, Walt Jr. Brake wrote:
> > On 2/11/2021 17:05, Mathias Nyman wrote:
> >> On 1.11.2021 16.06, Alan Stern wrote:
> >>> On Sat, Oct 30, 2021 at 12:49:37PM +0800, Walt Jr. Brake wrote:
> >>>> This patch make USB 3.1 device cannot be detected, and I report the bug [1]
> >>>> to archlinux three month ago. Yesterday I try to fix it myself, and after I
> >>>> revert this patch, compile the kernel and test, it works.
> >>>>
> >>>> [1] https://bugs.archlinux.org/task/71660?project=1&pagenum=2
> >>>>
> >>>>
> >>>> diff --git a/drivers/usb/core/hub.h b/drivers/usb/core/hub.h
> >>>> index 22ea1f4f2d66..73f4482d833a 100644
> >>>> --- a/drivers/usb/core/hub.h
> >>>> +++ b/drivers/usb/core/hub.h
> >>>> @@ -148,10 +148,8 @@ static inline unsigned hub_power_on_good_delay(struct
> >>>> usb_hub *hub)
> >>>>   {
> >>>>          unsigned delay = hub->descriptor->bPwrOn2PwrGood * 2;
> >>>>
> >>>> -       if (!hub->hdev->parent) /* root hub */
> >>>> -               return delay;
> >>>> -       else /* Wait at least 100 msec for power to become stable */
> >>>> -               return max(delay, 100U);
> >>>> +       /* Wait at least 100 msec for power to become stable */
> >>>> +       return max(delay, 100U);
> >>>>   }
> >>> Mathias:
> >>>
> >>> It looks like the bPwrOn2PwrGood value in xhci-hcd's hub descriptor is
> >>> too small for some USB 3.1 devices.
> >>>
> >>> Can you look into this?
> >>>
> >>> Alan Stern
> >>>
> >> At first glance the xhci roothub bPwrOn2PwrGood value looks ok.
> >> xhci spec 5.4.8 states software should wait 20ms after asserting PP, before
> >> attempting to change the state of the port.
> >>
> >> xhci driver sets desc->bPwrOn2PwrGood = 10; (2ms interval, so equals 20ms )
> >>
> >> We should probably get this working immediately, so maybe revert that patch
> >> while looking into the rootcause.
> >>
> >> Walt Jr. Brake, instead of reverting that patch, could you test if changing the
> >> xhci roothub bPwrOn2PwrGood value helps.
> >>
> >> diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
> >> index a3f875eea751..756231a55602 100644
> >> --- a/drivers/usb/host/xhci-hub.c
> >> +++ b/drivers/usb/host/xhci-hub.c
> >> @@ -257,7 +257,7 @@ static void xhci_common_hub_descriptor(struct xhci_hcd *xhci,
> >>   {
> >>          u16 temp;
> >>   -       desc->bPwrOn2PwrGood = 10;      /* xhci section 5.4.9 says 20ms max */
> >> +       desc->bPwrOn2PwrGood = 50;      /* The 20ms in xhci 5.4.8 isn't enough for USB 3.1 */
> >>          desc->bHubContrCurrent = 0;
> >>            desc->bNbrPorts = ports;
> >>
> >> Thanks
> >> -Mathias
> > 
> > Mathias:
> > 
> > Sorry to reply lately. I test with your patch, it works.
> > 
> > I also test with setting bPwrOn2PwrGood to 45, and it not work.
> > 
> > Seems that the minimal value should be 50 for this case.
> > 
> 
> Thanks for testing, and for checking that 90ms wait isn't enough

Can you send a "real" patch for this so I can get it into the tree soon
to resolve the regression?

thanks,

greg k-h