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

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Date:   Tue, 15 Feb 2022 12:16:12 +0200
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Pavan Kondeti <quic_pkondeti@...cinc.com>
Cc:     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

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.

Then dig into the reason why xhci_stop(), xhci_resume() and xhci_shutdown() call
xhci_reset() witch spin_lock_irq() held.

-Mathias