linux-kernel - Re: usb: host: Reduce xhci_handshake timeout in xhci

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Message-ID: <20220211064630.GA20567@hu-pkondeti-hyd.qualcomm.com>
Date:   Fri, 11 Feb 2022 12:16:30 +0530
From:   Pavan Kondeti <quic_pkondeti@...cinc.com>
To:     Mathias Nyman <mathias.nyman@...el.com>
CC:     Jung Daehwan <dh10.jung@...sung.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <quic_udipto@...cinc.com>
Subject: Re: usb: host: Reduce xhci_handshake timeout in xhci_reset

On Mon, Jun 28, 2021 at 10:49:00AM +0300, Mathias Nyman wrote:
> On 28.6.2021 9.55, Jung Daehwan wrote:
> > On Mon, Jun 28, 2021 at 08:53:02AM +0200, Greg Kroah-Hartman wrote:
> >> On Mon, Jun 28, 2021 at 11:25:48AM +0900, Jung Daehwan wrote:
> >>> On Tue, Jun 22, 2021 at 09:56:20PM +0200, Greg Kroah-Hartman wrote:
> >>>> On Tue, Jun 22, 2021 at 08:24:56PM +0900, Daehwan Jung wrote:
> >>>>> It seems 10 secs timeout is too long in general case. A core would wait for
> >>>>> 10 secs without doing other task and it can be happended on every device.
> >>>>
> >>>> Only if the handshake does not come back sooner, right?
> >>>
> >>> Yes, right.
> >>>
> >>>> What is causing your device to timeout here?
> >>>
> >>> Host Controller doesn't respond handshake. I don't know why and I ask HW team
> >>> to debug it.
> >>
> >> Please work to fix your hardware, that feels like the root of the
> >> problem here.  If you require the timeout for xhci_reset() to happen,
> >> then how do you know that the hardware really did reset properly in the
> >> reduced amount of time you just provided?
> >>
> > 
> > I continue fixing this issue with hardware engineer, but currently just
> > host controller can crash whole system and that's why I want to fix it.
> > How about adding some error logs in this situation for recognizing this issue?
> > We can add error log in xhci_stop as xhci_reset can returns error like below.
> > 
> > static void xhci_stop(struct usb_hcd *hcd)
> > {
> >         u32 temp;
> >         struct xhci_hcd *xhci = hcd_to_xhci(hcd);
> > +       int ret;
> > 
> >         mutex_lock(&xhci->mutex);
> > 
> > @@ -733,6 +734,9 @@ static void xhci_stop(struct usb_hcd *hcd)
> >         xhci->cmd_ring_state = CMD_RING_STATE_STOPPED;
> >         xhci_halt(xhci);
> >         xhci_reset(xhci);
> > +       if (ret)
> > +               xhci_err(xhci, "%s: Error while reset xhci Host controller - ret = %d\n"
> > +                       , __func__, ret);
> >         spin_unlock_irq(&xhci->lock);
> > 
> 
> We can check the xhci_reset() return value here and print a message, makes sense.
> 
> The original reason for the 10 second timeout was because a host actually took 9 seconds:
> 
> commit 22ceac191211cf6688b1bf6ecd93c8b6bf80ed9b
> 
>     xhci: Increase reset timeout for Renesas 720201 host.
>     
>     The NEC/Renesas 720201 xHCI host controller does not complete its reset
>     within 250 milliseconds.  In fact, it takes about 9 seconds to reset the
>     host controller, and 1 second for the host to be ready for doorbell
>     rings.  Extend the reset and CNR polling timeout to 10 seconds each.
> 
Agreed.

We also run into the similar issue (very very rarely reproduced) on
our platforms like SM8450. The issue happens when host mode is de-activated
(type-c cable disconnected). Since xhci_reset() is called with interrupts
disabled, a timeout of 10 seconds is fatal to the system.

Thanks,
Pavan