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

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Message-Id: <EF6B47D0-973E-46B7-9194-C58389FFAB35@canonical.com>
Date:   Mon, 8 Jun 2020 11:58:40 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     mathias.nyman@...el.com
Cc:     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 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...

> ---
> drivers/usb/host/xhci.c | 3 +++
> 1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> index 14181a7ea375..1058f604975b 100644
> --- a/drivers/usb/host/xhci.c
> +++ b/drivers/usb/host/xhci.c
> @@ -4474,6 +4474,9 @@ static int xhci_set_usb2_hardware_lpm(struct usb_hcd *hcd,
> 			mutex_lock(hcd->bandwidth_mutex);
> 			xhci_change_max_exit_latency(xhci, udev, 0);
> 			mutex_unlock(hcd->bandwidth_mutex);
> +			readl_poll_timeout(ports[port_num]->addr, pm_val,
> +					   (pm_val & PORT_PLS_MASK) == XDEV_U0,
> +					   100, 10000);
> 			return 0;
> 		}
> 	}
> -- 
> 2.17.1
>