linux-kernel - Re: [PATCH 2/2] xhci: Poll for U0 after disabling USB2 LPM

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Date:   Tue, 23 Jun 2020 11:38:33 +0300
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] xhci: Poll for U0 after disabling USB2 LPM

On 19.6.2020 17.19, Kai-Heng Feng wrote:
> Hi Mathias,
> 
>> On Jun 9, 2020, at 18:15, Kai-Heng Feng <kai.heng.feng@...onical.com> wrote:
>>
>>
>>
>>> On Jun 8, 2020, at 19:21, Mathias Nyman <mathias.nyman@...ux.intel.com> wrote:
>>>
>>> On 20.5.2020 13.18, Kai-Heng Feng wrote:
>>>> USB2 devices with LPM enabled may interrupt the system suspend:
>>>> [  932.510475] usb 1-7: usb suspend, wakeup 0
>>>> [  932.510549] hub 1-0:1.0: hub_suspend
>>>> [  932.510581] usb usb1: bus suspend, wakeup 0
>>>> [  932.510590] xhci_hcd 0000:00:14.0: port 9 not suspended
>>>> [  932.510593] xhci_hcd 0000:00:14.0: port 8 not suspended
>>>> ..
>>>> [  932.520323] xhci_hcd 0000:00:14.0: Port change event, 1-7, id 7, portsc: 0x400e03
>>>
>>> 400e03 = Connected, Enabled, U0 with port ink state change flag (PLC) set.
>>>
>>>> ..
>>>> [  932.591405] PM: pci_pm_suspend(): hcd_pci_suspend+0x0/0x30 returns -16
>>>> [  932.591414] PM: dpm_run_callback(): pci_pm_suspend+0x0/0x160 returns -16
>>>> [  932.591418] PM: Device 0000:00:14.0 failed to suspend async: error -16
>>>>
>>>> During system suspend, USB core will let HC suspends the device if it
>>>> doesn't have remote wakeup enabled and doesn't have any children.
>>>> However, from the log above we can see that the usb 1-7 doesn't get bus
>>>> suspended due to not in U0. After a while the port finished U2 -> U0
>>>> transition, interrupts the suspend process.
>>>
>>> In USB2 HW link PM the PLC flag should not be set in U2Exit -> U0 transitions.
>>> Only case we should see a port change event is U2Entry -> U0 due to STALL or
>>> error/timeout. (see xhci 4.23.5.1.1.1)
>>>
>>>>
>>>> The observation is that after disabling LPM, port doesn't transit to U0
>>>> immediately and can linger in U2. xHCI spec 4.23.5.2 states that the
>>>> maximum exit latency for USB2 LPM should be BESL + 10us. The BESL for
>>>> the affected device is advertised as 400us, which is still not enough
>>>> based on my testing result.
>>>>
>>>> So let's use the maximum permitted latency, 10000, to poll for U0
>>>> status to solve the issue.
>>>
>>> I don't recall all details, but it could be that disabling LPM before suspend
>>> is unnecessary. 
>>> At least xhci should be able to set a port to U3 from U1 and U2 (see xhci 4.15.1)
>>> so that is one change that could be done to xhci_bus_suspend()
>>
>> Yes, put the device to U3 directly does the trick.
> 
> As discussed, will you pick this series over the v2?
> Or is there anything I should improve for this one?
> 
> Kai-Heng

Added this to queueI

Thanks
-Mathias