linux-kernel - Re: [DISCUSSION] USB device remote wakeup is not working for S3 case

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Date:	Thu, 18 Dec 2014 10:35:48 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Du, Changbin" <changbin.du@...el.com>
cc:	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [DISCUSSION] USB device remote wakeup is not working for S3 case

Please tell your email client to wrap lines after 72 columns or so.

On Thu, 18 Dec 2014, Du, Changbin wrote:

> When I am checking usb remote wakeup code, I found that usb remote
> wakeup will not work after system going to S3 sate and I confirmed
> with my PC.

USB remote _does_ work.

> During enumeration, usb device will be set as wakeup capable by
> usb_set_device_state if it supports. Whether usb driver send
> SET_FEATURE(REMOTE_WAKUP) usb request when suspending on S3 depend on
> do_remote_wakeup flag which is set by choose_wakeup(). It can be
> simply presented as below.
>        do_remote_wakeup  = device_may_wakeup(&udev->dev);

That's right.

> The return value is always false since usb device is not marked as
> wakeup enabled(that is no one call device_set_wakeup_enable() for usb
> device). As a result, usb device will not signal wakeup event to
> host.

There's a simple solution: Call device_set_wakeup_enable() for the
device!  You can do this from the command line by:

	echo auto >/sys/bus/usb/devices/.../power/control

where the "..." is the pathname for your device.

> Maybe we should not allow all remote wakeup supported device can
> wakeup system by default. But for usb keyboard/mouse, I think it is
> not reasonable to disable it by default.

For USB keyboards, wakeup _is_ enabled by default.  See this section of 
code close to the end of usbhid_start():

	/* Some keyboards don't work until their LEDs have been set.
	 * Since BIOSes do set the LEDs, it must be safe for any device
	 * that supports the keyboard boot protocol.
	 * In addition, enable remote wakeup by default for all keyboard
	 * devices supporting the boot protocol.
	 */
	if (interface->desc.bInterfaceSubClass == USB_INTERFACE_SUBCLASS_BOOT &&
			interface->desc.bInterfaceProtocol ==
				USB_INTERFACE_PROTOCOL_KEYBOARD) {
		usbhid_set_leds(hid);
		device_set_wakeup_enable(&dev->dev, 1);
	}

> A simple way to fix this is that replace the device_may_wakeup by
> device_can_wakeup in choose_wakeup() function, just like on auto
> suspend case (usb remote wakeup works for rpm). Another way is to
> make usb device wakeup able by default. But both of them will make
> all usb devices can wakeup system. Have any better idea?

How about leaving everything the way it is now?  If you want to enable 
wakeup for something like a USB mouse, you can write a udev script to 
do it as shown above.

Alan Stern

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