linux-kernel - Re: [PATCH v2] xhci: reduce xhci_handshake timeout in xhci

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Message-ID: <20220215104920.GE31021@hu-pkondeti-hyd.qualcomm.com>
Date:   Tue, 15 Feb 2022 16:19:20 +0530
From:   Pavan Kondeti <quic_pkondeti@...cinc.com>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>
CC:     Pavan Kondeti <quic_pkondeti@...cinc.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <quic_ugoswami@...cinc.com>, Jung Daehwan <dh10.jung@...sung.com>
Subject: Re: [PATCH v2] xhci: reduce xhci_handshake timeout in xhci_reset

Hi Mathias,

On Tue, Feb 15, 2022 at 12:16:12PM +0200, Mathias Nyman wrote:
> On 14.2.2022 15.53, Pavan Kondeti wrote:
> > Hi Mathias,
> > 
> > On Mon, Feb 14, 2022 at 02:51:54PM +0200, Mathias Nyman wrote:
> >> On 14.2.2022 14.20, Pavankumar Kondeti wrote:
> >>> From: Daehwan Jung <dh10.jung@...sung.com>
> >>>
> >>> xhci_reset() is called with interrupts disabled. Waiting 10 seconds for
> >>> controller reset and controller ready operations can be fatal to the
> >>> system when controller is timed out. Reduce the timeout to 1 second
> >>> and print a error message when the time out happens.
> >>>
> >>> Fixes: 22ceac191211 ("xhci: Increase reset timeout for Renesas 720201 host.")
> >>
> >>
> >> The commit 22ceac191211 ("xhci: Increase reset timeout for Renesas 720201 host.")
> >> intentionally increased the timeout to 10 seconds as that host might take 9
> >> seconds to complete reset. This was done almost 10 years ago so I don't know
> >> if it really is an issue anymore.
> >>
> >> Anyways, your patch might break Renesas 72021 instead of fixing it.
> > 
> > Unfortunately, yes :-( . We have this reduced timeout patch in our previous
> > commercialized products so thought this would be a good time to fix this
> > once for all. Since this patch has been 10 years long, not sure if any other
> > controllers also need 10 sec timeout. It would probably better
> > 
> >>
> >> I agree that busylooping up to 10 seconds with interrupts disabled doesn't make sense.
> >>
> >> Lets see if there is another solution for your case.
> >>
> >> - Does a "guard interval" after writing the reset help?
> >>   For example Intel xHCI needs 1ms before touching xHC after writing the reset bit
> > 
> > I will ask this question to our hardware team. Setting that one quirk from
> > DWC3 host might require other changes like this [1].
> >>
> >> - Is it the CNR bit or the RESET bit that fails? could be just stuck CNR bit? 
> > 
> > The RESET bit never gets cleared from USBCMD register.
> > 
> >>  
> >> - we only disable local interrupts when xhci_reset() is called from xhci_stop(),
> >>   and sometimes from xhci_shutdown() and xhci_resume() if some conditions are met.
> >>   Have you identified which one is the problematic case?
> > 
> > The crash reports I have seen are pointing to
> > 
> > usb_remove_hcd()->xhci_stop()->xhci_reset()
> 
> Ok, so xhci_stop() and xhci_shutdown() both may call xhci_reset() with interrupts
> disabled and spinlock held. In both these cases we're not that interested in the
> outcome of xhci_reset().
> 
> But during probe we call xhci_reset() with interrupts enabled without spinlock,
> and here we really care about it succeeding.
> I'm also guessing reset could take a longer time during probe due to possible recent
> BIOS handover, or firmware loading etc.
> 
> So how about passing a timeout value to xhci_reset()?
> Give it 10 seconds during probe, and 250ms in the other cases.
> 

Thanks for this suggestion.

This sounds better compared to the quirks approach. xhci_resume() also seems
to be calling xhci_reset() in the hibernation path, I believe we should treat
this like probe()/startup case and give larger timeout.

Thanks,
Pavan