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

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