linux-kernel - Re: [PATCH] USB: Increment wakeup count on remote wakeup.

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Date:   Thu, 19 Apr 2018 09:17:40 -0700
From:   Rajat Jain <rajatja@...gle.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Ravi Chandra Sadineni <ravisadineni@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        martin.blumenstingl@...glemail.com,
        Ravi Chandra Sadineni <ravisadineni@...gle.com>,
        chunfeng.yun@...iatek.com, johan@...nel.org,
        arvind.yadav.cs@...il.com, Dmitry Torokhov <dtor@...gle.com>,
        anton.bondarenko.sama@...il.com, f.fainelli@...il.com,
        keescook@...omium.org, mathias.nyman@...ux.intel.com,
        felipe.balbi@...ux.intel.com, ekorenevsky@...il.com,
        peter.chen@....com, joe@...ches.com,
        Todd Broch <tbroch@...gle.com>, linux-usb@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Benson Leung <bleung@...gle.com>
Subject: Re: [PATCH] USB: Increment wakeup count on remote wakeup.

On Thu, Apr 19, 2018 at 8:01 AM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Wed, 18 Apr 2018, Ravi Chandra Sadineni wrote:
>
>> On chromebooks we depend on wakeup count to identify the wakeup source.
>> But currently USB devices do not increment the wakeup count when they
>> trigger the remote wake. This patch addresses the same.
>>
>> Resume condition is reported differently on USB 2.0 and USB 3.0 devices.
>>
>> On USB 2.0 devices, a wake capable device, if wake enabled, drives
>> resume signal to indicate a remote wake (USB 2.0 spec section 7.1.7.7).
>> The upstream facing port then sets C_PORT_SUSPEND bit and reports a
>> port change event (USB 2.0 spec section 11.24.2.7.2.3). Thus if a port
>> has resumed before driving the resume signal from the host and
>> C_PORT_SUSPEND is set, then the device attached to the given port might
>> be the reason for the last system wakeup. Increment the wakeup count for
>> the same.
>>
>> On USB 3.0 devices, a function may signal that it wants to exit from device
>> suspend by sending a Function Wake Device Notification to the host (USB3.0
>> spec section 8.5.6.4) Thus on receiving the Function Wake, increment the
>> wakeup count.
>>
>> Signed-off-by: ravisadineni@...omium.org
>> ---
>>  drivers/usb/core/hcd.c |  1 +
>>  drivers/usb/core/hub.c | 12 ++++++++++--
>>  2 files changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
>> index 777036ae63674..79f95a878fb6e 100644
>> --- a/drivers/usb/core/hcd.c
>> +++ b/drivers/usb/core/hcd.c
>> @@ -2375,6 +2375,7 @@ void usb_hcd_resume_root_hub (struct usb_hcd *hcd)
>>  {
>>       unsigned long flags;
>>
>> +     pm_wakeup_event(dev, 0);
>
> Instead of dev, you probably want to use hcd->self.sysdev.  Or maybe
> hcd->self.controller, although the difference probably doesn't matter
> for your purposes.
>
> On the other hand, this wakeup event may already have been counted by
> the host controller's bus subsystem.  Does it matter if the same wakeup
> event gets counted twice?

No. The context is that we're interested in making user space behave
differently if the wake up source was a user input device (e.g. USB
keyboard) v/s some other kind of USB device. So all that matters is
that the USB device wakeup count gets incremented.

>
> (This is inevitable with USB devices, in any case.  If a device sends a
> wakeup request, it will be counted for that device, for all the
> intermediate hubs, and for the host controller.)
>
>> @@ -3432,10 +3437,13 @@ int usb_port_resume(struct usb_device *udev, pm_message_t msg)
>>
>>       usb_lock_port(port_dev);
>>
>> -     /* Skip the initial Clear-Suspend step for a remote wakeup */
>>       status = hub_port_status(hub, port1, &portstatus, &portchange);
>> -     if (status == 0 && !port_is_suspended(hub, portstatus))
>> +     /* Skip the initial Clear-Suspend step for a remote wakeup */
>
> What is the reason for moving the comment line down after the
> hub_port_status() call?
>
> Alan Stern
>
>> +     if (status == 0 && !port_is_suspended(hub, portstatus)) {
>> +             if (portchange & USB_PORT_STAT_C_SUSPEND)
>> +                     pm_wakeup_event(&udev->dev, 0);
>>               goto SuspendCleared;
>> +     }
>>
>>       /* see 7.1.7.7; affects power usage, but not budgeting */
>>       if (hub_is_superspeed(hub->hdev))
>>
>