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

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Date:   Mon, 1 Nov 2021 10:06:13 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Mathias Nyman <mathias.nyman@...el.com>,
        "Walt Jr. Brake" <mr.yming81@...il.com>
Cc:     Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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 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

> On 10/4/2021 09:20, Chunfeng Yun wrote:
> > Return the exactly delay time given by root hub descriptor,
> > this helps to reduce resume time etc.
> > 
> > Due to the root hub descriptor is usually provided by the host
> > controller driver, if there is compatibility for a root hub,
> > we can fix it easily without affect other root hub
> > 
> > Acked-by: Alan Stern<stern@...land.harvard.edu>
> > Signed-off-by: Chunfeng Yun<chunfeng.yun@...iatek.com>
> > ---
> > v2: remove RFC tag, and add acked-by Alan
> > ---
> >   drivers/usb/core/hub.h | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/usb/core/hub.h b/drivers/usb/core/hub.h
> > index 73f4482d833a..22ea1f4f2d66 100644
> > --- a/drivers/usb/core/hub.h
> > +++ b/drivers/usb/core/hub.h
> > @@ -148,8 +148,10 @@ static inline unsigned hub_power_on_good_delay(struct usb_hub *hub)
> >   {
> >   	unsigned delay = hub->descriptor->bPwrOn2PwrGood * 2;
> > -	/* Wait at least 100 msec for power to become stable */
> > -	return max(delay, 100U);
> > +	if (!hub->hdev->parent)	/* root hub */
> > +		return delay;
> > +	else /* Wait at least 100 msec for power to become stable */
> > +		return max(delay, 100U);
> >   }
> >   static inline int hub_port_debounce_be_connected(struct usb_hub *hub,