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

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Message-ID: <496c9d86-70d7-1050-5bbb-9f841e4b464a@intel.com>
Date:   Mon, 28 Jun 2021 10:49:00 +0300
From:   Mathias Nyman <mathias.nyman@...el.com>
To:     Jung Daehwan <dh10.jung@...sung.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: usb: host: Reduce xhci_handshake timeout in xhci_reset

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.

-Mathias