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

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Date:   Mon, 8 Jun 2020 09:05:24 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     mathias.nyman@...el.com,
        "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 Mon, Jun 08, 2020 at 11:58:40AM +0800, Kai-Heng Feng wrote:
> 
> 
> > On May 20, 2020, at 18:18, Kai-Heng Feng <kai.heng.feng@...onical.com> 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
> > ..
> > [  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.
> > 
> > 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.
> > 
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> 
> A gentle ping...

It is the middle of the merge window, we can't do anything with any new
patch until after -rc1 is out.

You know this...

greg k-h