Re: [PATCH V2] input: Fix USB autosuspend on bcm5974

[Oliver Neukum <oneukum@suse.de>]

Am Montag, 10. Oktober 2011, 15:41:26 schrieb Matthew Garrett:
> The bcm5974 code takes a USB autosuspend reference on device open and
> releases it on device close. This means that the hardware won't sleep when
> anything holds it open. This is sensible for input devices that don't
> support remote wakeups on normal use (like most mice), but this hardware
> trigger wakeups on touch and so can suspend transparently to the user. Doing
> so allows the USB host controller to sleep when the machine is idle, giving
> measurable power savings.
> 
> Signed-off-by: Matthew Garrett <mjg@redhat.com>
> ---
> 
> Got rid of the unbalanced put on the close path, and added usb_mark_last_busy()
> calls to make sure the device doesn't go to sleep while in use. This works fine
> on my hardware now, and I don't see any warning messages being generated.

This is odd, because the hardware shouldn't generate remote wakeups unless you
request them, like this (usbhid)

int usbhid_open(struct hid_device *hid)
{
        struct usbhid_device *usbhid = hid->driver_data;
        int res;

        mutex_lock(&hid_open_mut);
        if (!hid->open++) {
                res = usb_autopm_get_interface(usbhid->intf);
                /* the device must be awake to reliably request remote wakeup */
                if (res < 0) {
                        hid->open--;
                        mutex_unlock(&hid_open_mut);
                        return -EIO;
                }
                usbhid->intf->needs_remote_wakeup = 1;

	Regards
		Oliver