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

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Date:   Fri, 19 Jun 2020 22:19:46 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Mathias Nyman <mathias.nyman@...ux.intel.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

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

> 
>> 
>> Also just noticed that we are not really checking L1S field in PORTPMSC register, 
>> this should tell if there was an issue with USB2 lpm state transitions, and
>> perhaps we should disable lpm for that device. 
>> 
>> Does the L1S field show anything unuaual in your case?
>> That could explain the port event with the PLC bit set.
> 
> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> index 2c255d0620b0..a2099d42e490 100644
> --- a/drivers/usb/host/xhci-ring.c
> +++ b/drivers/usb/host/xhci-ring.c
> @@ -1592,7 +1592,7 @@ static void handle_port_status(struct xhci_hcd *xhci,
> {
>        struct usb_hcd *hcd;
>        u32 port_id;
> -       u32 portsc, cmd_reg;
> +       u32 portsc, portpmsc, cmd_reg;
>        int max_ports;
>        int slot_id;
>        unsigned int hcd_portnum;
> @@ -1634,9 +1634,10 @@ static void handle_port_status(struct xhci_hcd *xhci,
>        bus_state = &port->rhub->bus_state;
>        hcd_portnum = port->hcd_portnum;
>        portsc = readl(port->addr);
> +       portpmsc = readl(port->addr + PORTPMSC);
> 
> -       xhci_dbg(xhci, "Port change event, %d-%d, id %d, portsc: 0x%x\n",
> -                hcd->self.busnum, hcd_portnum + 1, port_id, portsc);
> +       xhci_dbg(xhci, "Port change event, %d-%d, id %d, portsc: 0x%x, portpmsc 0x%0x\n",
> +                hcd->self.busnum, hcd_portnum + 1, port_id, portsc, portpmsc);
> 
>        trace_xhci_handle_port_status(hcd_portnum, portsc);
> 
> [  685.460054] xhci_hcd 0000:00:14.0: Port change event, 1-7, id 7, portsc: 0x400e03, portpmsc 0x1
> [  685.460062] xhci_hcd 0000:00:14.0: resume root hub
> [  685.460079] xhci_hcd 0000:00:14.0: handle_port_status: starting port polling.
> [  685.460094] xhci_hcd 0000:00:14.0: xhci_hub_status_data: stopping port polling.
> [  685.521685] PM: pci_pm_suspend(): hcd_pci_suspend+0x0/0x30 returns -16
> [  685.521695] PM: dpm_run_callback(): pci_pm_suspend+0x0/0x160 returns -16
> [  685.521699] PM: Device 0000:00:14.0 failed to suspend async: error -16
> 
> So after disabling LPM, it takes a long time to complete L1 transition, before transitioning to L0.
> 
> Kai-Heng
> 
>> 
>> I think we can avoid a readl_poll_timeout() solution in this case.
>> 
>> -Mathias