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

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Message-ID: <20211105133050.GA1590803@rowland.harvard.edu>
Date:   Fri, 5 Nov 2021 09:30:50 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Mathias Nyman <mathias.nyman@...ux.intel.com>,
        "Walt Jr. Brake" <mr.yming81@...il.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Nishad Kamdar <nishadkamdar@...il.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Eddie Hung <eddie.hung@...iatek.com>
Subject: Re: [PATCH v2] usb: core: reduce power-on-good delay time of root hub

On Fri, Nov 05, 2021 at 11:00:31AM +0100, Greg Kroah-Hartman wrote:
> 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?

Also, it might make sense to move the desc->bPwrOn2PwrGood setting from 
xhci_common_hub_descriptor into the speed-specific routines.  For the 
USB-2 root hub the value can remain set to 10; only the USB-3 root hub 
needs to be changed.

Alan Stern