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

[Walt Jr. Brake]

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.