USB: implement usb_enable_autosuspend

This patch (as1326) adds usb_enable_autosuspend() and
usb_disable_autosuspend() routines for use by drivers.  If a driver
knows that its device can handle suspends and resumes correctly, it
can enable autosuspend all by itself.  This is equivalent to the user
writing "auto" to the device's power/level attribute.

The implementation differs slightly from what it used to be.  Now
autosuspend is disabled simply by doing usb_autoresume_device() (to
increment the usage counter) and enabled by doing
usb_autosuspend_device() (to decrement the usage counter).

The set_level() attribute method is updated to use the new routines,
and the USB Power-Management documentation is updated.

The patch adds a usb_enable_autosuspend() call to the hub driver's
probe routine, allowing the special-case code for hubs in quirks.c to
be removed.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

4 files changed, 56 insertions, 21 deletions

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 2b39583040d..057eeab0600 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -1415,6 +1415,48 @@ static int usb_resume_both(struct usb_device *udev, pm_message_t msg)
 
 #ifdef CONFIG_USB_SUSPEND
 
+/**
+ * usb_enable_autosuspend - allow a USB device to be autosuspended
+ * @udev: the USB device which may be autosuspended
+ *
+ * This routine allows @udev to be autosuspended.  An autosuspend won't
+ * take place until the autosuspend_delay has elapsed and all the other
+ * necessary conditions are satisfied.
+ *
+ * The caller must hold @udev's device lock.
+ */
+int usb_enable_autosuspend(struct usb_device *udev)
+{
+	if (udev->autosuspend_disabled) {
+		udev->autosuspend_disabled = 0;
+		usb_autosuspend_device(udev);
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(usb_enable_autosuspend);
+
+/**
+ * usb_disable_autosuspend - prevent a USB device from being autosuspended
+ * @udev: the USB device which may not be autosuspended
+ *
+ * This routine prevents @udev from being autosuspended and wakes it up
+ * if it is already autosuspended.
+ *
+ * The caller must hold @udev's device lock.
+ */
+int usb_disable_autosuspend(struct usb_device *udev)
+{
+	int rc = 0;
+
+	if (!udev->autosuspend_disabled) {
+		rc = usb_autoresume_device(udev);
+		if (rc == 0)
+			udev->autosuspend_disabled = 1;
+	}
+	return rc;
+}
+EXPORT_SYMBOL_GPL(usb_disable_autosuspend);
+
 /* Internal routine to adjust a device's usage counter and change
  * its autosuspend state.
  */
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index bfa6123bbdb..746f26f222a 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1224,6 +1224,9 @@ static int hub_probe(struct usb_interface *intf, const struct usb_device_id *id)
 	desc = intf->cur_altsetting;
 	hdev = interface_to_usbdev(intf);
 
+	/* Hubs have proper suspend/resume support */
+	usb_enable_autosuspend(hdev);
+
 	if (hdev->level == MAX_TOPO_LEVEL) {
 		dev_err(&intf->dev,
 			"Unsupported bus topology: hub nested too deep\n");
diff --git a/drivers/usb/core/quirks.c b/drivers/usb/core/quirks.c
index 0b689224394..4314f259524 100644
--- a/drivers/usb/core/quirks.c
+++ b/drivers/usb/core/quirks.c
@@ -103,11 +103,10 @@ void usb_detect_quirks(struct usb_device *udev)
 		dev_dbg(&udev->dev, "USB quirks for this device: %x\n",
 				udev->quirks);
 
-	/* By default, disable autosuspend for all non-hubs */
-#ifdef	CONFIG_USB_SUSPEND
-	if (udev->descriptor.bDeviceClass != USB_CLASS_HUB)
-		udev->autosuspend_disabled = 1;
-#endif
+	/* By default, disable autosuspend for all devices.  The hub driver
+	 * will enable it for hubs.
+	 */
+	usb_disable_autosuspend(udev);
 
 	/* For the present, all devices default to USB-PERSIST enabled */
 #if 0		/* was: #ifdef CONFIG_PM */
diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c
index 5a1a0e2b647..313e241f5cc 100644
--- a/drivers/usb/core/sysfs.c
+++ b/drivers/usb/core/sysfs.c
@@ -389,34 +389,25 @@ set_level(struct device *dev, struct device_attribute *attr,
 	struct usb_device *udev = to_usb_device(dev);
 	int len = count;
 	char *cp;
-	int rc = 0;
-	int old_autosuspend_disabled;
+	int rc;
 
 	cp = memchr(buf, '\n', count);
 	if (cp)
 		len = cp - buf;
 
 	usb_lock_device(udev);
-	old_autosuspend_disabled = udev->autosuspend_disabled;
 
-	/* Setting the flags without calling usb_pm_lock is a subject to
-	 * races, but who cares...
-	 */
 	if (len == sizeof on_string - 1 &&
-			strncmp(buf, on_string, len) == 0) {
-		udev->autosuspend_disabled = 1;
-		rc = usb_external_resume_device(udev, PMSG_USER_RESUME);
+			strncmp(buf, on_string, len) == 0)
+		rc = usb_disable_autosuspend(udev);
 
-	} else if (len == sizeof auto_string - 1 &&
-			strncmp(buf, auto_string, len) == 0) {
-		udev->autosuspend_disabled = 0;
-		rc = usb_external_resume_device(udev, PMSG_USER_RESUME);
+	else if (len == sizeof auto_string - 1 &&
+			strncmp(buf, auto_string, len) == 0)
+		rc = usb_enable_autosuspend(udev);
 
-	} else
+	else
 		rc = -EINVAL;
 
-	if (rc)
-		udev->autosuspend_disabled = old_autosuspend_disabled;
 	usb_unlock_device(udev);
 	return (rc < 0 ? rc : count);
 }