linux-kernel - Re: [PATCH 1/3] xhci: Ensure link state is U3 after setting USB_SS_PORT_LS

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Message-ID: <CAAd53p5a2RFpZuHGvuNO_9kgv4dGhHCYU0jeq44FtKJv0Ky8uA@mail.gmail.com>
Date:   Mon, 13 Jan 2020 17:10:02 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        AceLan Kao <acelan.kao@...onical.com>,
        USB list <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] xhci: Ensure link state is U3 after setting USB_SS_PORT_LS_U3

On Fri, Jan 10, 2020 at 5:33 PM Mathias Nyman
<mathias.nyman@...ux.intel.com> wrote:
>
> On 3.1.2020 10.40, Kai-Heng Feng wrote:
> > The xHCI spec doesn't specify the upper bound of U3 transition time. For
> > some devices 20ms is not enough, so we need to make sure the link state
> > is in U3 before further actions.
>
> Looking at the USB 3.2 spec (7.2.4.2 Link Power management and Flow) it seems
> most timers related to U3 entry are a lot less than a millisecond (4-16us)
> If port is in U1/U2,  Ux_EXIT_TIMER is 6ms which seems to be the longest timeout.
>
> If we anyway are polling for the U3 state we could shorten the initial 20ms sleep
> down to 10ms. I think many devices, especially if they are already in U0
> could manage this.

Ok.

>
> are >
> > I've tried to use U3 Entry Capability by setting U3 Entry Enable in
> > config register, however the port change event for U3 transition
> > interrupts the system suspend process.
> >
> > For now let's use the less ideal method by polling PLS.
> >
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> > ---
> >   drivers/usb/host/xhci-hub.c | 13 +++++++++++--
> >   1 file changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
> > index 7a3a29e5e9d2..2b2e9d004dbf 100644
> > --- a/drivers/usb/host/xhci-hub.c
> > +++ b/drivers/usb/host/xhci-hub.c
> > @@ -1228,6 +1228,7 @@ int xhci_hub_control(struct usb_hcd *hcd, u16 typeReq, u16 wValue,
> >                       break;
> >               case USB_PORT_FEAT_LINK_STATE:
> >                       temp = readl(ports[wIndex]->addr);
> > +                     xhci_dbg(xhci, "before setting link state, actual port %d-%d status = 0x%0x\n", hcd->self.busnum, wIndex + 1, temp);
>
> xhci_set_link_state() already shows similar debugging,

Ok, will remove it.

>
> >                       /* Disable port */
> >                       if (link_state == USB_SS_PORT_LS_SS_DISABLED) {
> >                               xhci_dbg(xhci, "Disable port %d\n", wIndex);
> > @@ -1316,9 +1317,17 @@ int xhci_hub_control(struct usb_hcd *hcd, u16 typeReq, u16 wValue,
> >                       msleep(20); /* wait device to enter */
> >                       spin_lock_irqsave(&xhci->lock, flags);
> >
> > -                     temp = readl(ports[wIndex]->addr);
> > -                     if (link_state == USB_SS_PORT_LS_U3)
> > +                     if (link_state == USB_SS_PORT_LS_U3) {
> > +                             retval = xhci_handshake(ports[wIndex]->addr, PORT_PLS_MASK, XDEV_U3, 80 * 1000);
> > +                             if (retval)
> > +                                     xhci_dbg(xhci, "polling XDEV_U3 on port %d-%d timeout\n", hcd->self.busnum, wIndex + 1);
>
> In worst case we are busylooping for 80ms here, keeping the cpu busy.
> It should be ok to sleep here, so how about just reading the register
> every 10ms max 10 times, sleeping in between.

Ok. Is the polling safe outside of spin_lock_irqsave()?

Kai-Heng

>
> -Mathias