[PATCH v2 2/2][SRU][B] xhci: Poll for U0 after disabling USB2 LPM

[Juerg Haefliger]

On Wed, 15 Jul 2020 11:30:49 +0800
Hsuan-Yu Lin <shane.lin at canonical.com> wrote:

> From: Kai-Heng Feng <kai.heng.feng at canonical.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1880519
> 
> 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.
> 
> Cc: stable at vger.kernel.org
> Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
> Signed-off-by: Mathias Nyman <mathias.nyman at linux.intel.com>
> Link: https://lore.kernel.org/r/20200624135949.22611-6-mathias.nyman@linux.intel.com
> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> (backported from commit b3d71abd135e6919ca0b6cab463738472653ddfb)

We typically like to see some info about why this wasn't a clean cherry
pick in the form of:
[<nick>: blabla]
so a reviewer has a chance to judge how different the backport is from the
original.

like:
[juergh: Trivial context adjustments due to SAUCE patch.]

...Juerg


> Signed-off-by: Hsuan-Yu Lin <shane.lin at canonical.com>
> ---
>  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 984ed8181bc2..5e8b4054aa0e 100644
> --- a/drivers/usb/host/xhci.c
> +++ b/drivers/usb/host/xhci.c
> @@ -4249,6 +4249,9 @@ 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(port_array[port_num], pm_val,
> +					   (pm_val & PORT_PLS_MASK) == XDEV_U0,
> +					   100, 10000);
>  			return 0;
>  		}
>  	}

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