USB: add power/level sysfs attribute

This patch (as874) adds another piece to the user-visible part of the
USB autosuspend interface. The new power/level sysfs attribute allows
users to force the device on (with autosuspend off), force the device
to sleep (with autoresume off), or return to normal automatic operation.

Signed-off-by: Alan Stern <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/ABI/testing/sysfs-bus-usb

···
 
 		The autosuspend delay for newly-created devices is set to
 		the value of the usbcore.autosuspend module parameter.
+
+What:		/sys/bus/usb/devices/.../power/level
+Date:		March 2007
+KernelVersion:	2.6.21
+Contact:	Alan Stern <[e-mail]>
+Description:
+		Each USB device directory will contain a file named
+		power/level.  This file holds a power-level setting for
+		the device, one of "on", "auto", or "suspend".
+
+		"on" means that the device is not allowed to autosuspend,
+		although normal suspends for system sleep will still
+		be honored.  "auto" means the device will autosuspend
+		and autoresume in the usual manner, according to the
+		capabilities of its driver.  "suspend" means the device
+		is forced into a suspended state and it will not autoresume
+		in response to I/O requests.  However remote-wakeup requests
+		from the device may still be enabled (the remote-wakeup
+		setting is controlled separately by the power/wakeup
+		attribute).
+
+		During normal use, devices should be left in the "auto"
+		level.  The other levels are meant for administrative uses.
+		If you want to suspend a device immediately but leave it
+		free to wake up in response to I/O requests, you should
+		write "0" to power/autosuspend.

drivers/usb/core/driver.c

···
 
 done:
 	// dev_dbg(&udev->dev, "%s: status %d\n", __FUNCTION__, status);
-	if (status == 0)
+	if (status == 0) {
+		udev->autoresume_disabled = 0;
 		udev->dev.power.power_state.event = PM_EVENT_ON;
+	}
 	return status;
 }
 
···
 	udev->do_remote_wakeup = device_may_wakeup(&udev->dev);
 	if (udev->pm_usage_cnt > 0)
 		return -EBUSY;
-	if (udev->autosuspend_delay < 0)
+	if (udev->autosuspend_delay < 0 || udev->autosuspend_disabled)
 		return -EPERM;
 
 	if (udev->actconfig) {
···
 	struct usb_interface	*intf;
 	struct usb_device	*parent = udev->parent;
 
+	if (udev->auto_pm && udev->autoresume_disabled)
+		return -EPERM;
 	cancel_delayed_work(&udev->autosuspend);
 	if (udev->state == USB_STATE_NOTATTACHED)
 		return -ENODEV;
···
 
 static int usb_resume(struct device *dev)
 {
+	struct usb_device	*udev;
+
 	if (!is_usb_device(dev))	/* Ignore PM for interfaces */
 		return 0;
-	return usb_external_resume_device(to_usb_device(dev));
+	udev = to_usb_device(dev);
+	if (udev->autoresume_disabled)
+		return -EPERM;
+	return usb_external_resume_device(udev);
 }
 
 #else

drivers/usb/core/quirks.c

···
 {
 #ifdef	CONFIG_USB_SUSPEND
 	/* disable autosuspend, but allow the user to re-enable it via sysfs */
-	udev->autosuspend_delay = 0;
+	udev->autosuspend_disabled = 1;
 #endif
 }
 

drivers/usb/core/sysfs.c

···
 
 
 #include <linux/kernel.h>
+#include <linux/string.h>
 #include <linux/usb.h>
 #include "usb.h"
 
···
 	if (value >= 0)
 		usb_try_autosuspend_device(udev);
 	else {
-		usb_lock_device(udev);
-		usb_external_resume_device(udev);
-		usb_unlock_device(udev);
+		if (usb_autoresume_device(udev) == 0)
+			usb_autosuspend_device(udev);
 	}
 	return count;
 }
···
 static DEVICE_ATTR(autosuspend, S_IRUGO | S_IWUSR,
 		show_autosuspend, set_autosuspend);
 
+static const char on_string[] = "on";
+static const char auto_string[] = "auto";
+static const char suspend_string[] = "suspend";
+
+static ssize_t
+show_level(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct usb_device *udev = to_usb_device(dev);
+	const char *p = auto_string;
+
+	if (udev->state == USB_STATE_SUSPENDED) {
+		if (udev->autoresume_disabled)
+			p = suspend_string;
+	} else {
+		if (udev->autosuspend_disabled)
+			p = on_string;
+	}
+	return sprintf(buf, "%s\n", p);
+}
+
+static ssize_t
+set_level(struct device *dev, struct device_attribute *attr,
+		const char *buf, size_t count)
+{
+	struct usb_device *udev = to_usb_device(dev);
+	int len = count;
+	char *cp;
+	int rc = 0;
+
+	cp = memchr(buf, '\n', count);
+	if (cp)
+		len = cp - buf;
+
+	usb_lock_device(udev);
+
+	/* 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;
+		udev->autoresume_disabled = 0;
+		rc = usb_external_resume_device(udev);
+
+	} else if (len == sizeof auto_string - 1 &&
+			strncmp(buf, auto_string, len) == 0) {
+		udev->autosuspend_disabled = 0;
+		udev->autoresume_disabled = 0;
+		rc = usb_external_resume_device(udev);
+
+	} else if (len == sizeof suspend_string - 1 &&
+			strncmp(buf, suspend_string, len) == 0) {
+		udev->autosuspend_disabled = 0;
+		udev->autoresume_disabled = 1;
+		rc = usb_external_suspend_device(udev, PMSG_SUSPEND);
+
+	} else
+		rc = -EINVAL;
+
+	usb_unlock_device(udev);
+	return (rc < 0 ? rc : count);
+}
+
+static DEVICE_ATTR(level, S_IRUGO | S_IWUSR, show_level, set_level);
+
 static char power_group[] = "power";
 
 static int add_power_attributes(struct device *dev)
 {
 	int rc = 0;
 
-	if (is_usb_device(dev))
+	if (is_usb_device(dev)) {
 		rc = sysfs_add_file_to_group(&dev->kobj,
 				&dev_attr_autosuspend.attr,
 				power_group);
+		if (rc == 0)
+			rc = sysfs_add_file_to_group(&dev->kobj,
+					&dev_attr_level.attr,
+					power_group);
+	}
 	return rc;
 }
 
 static void remove_power_attributes(struct device *dev)
 {
+	sysfs_remove_file_from_group(&dev->kobj,
+			&dev_attr_level.attr,
+			power_group);
 	sysfs_remove_file_from_group(&dev->kobj,
 			&dev_attr_autosuspend.attr,
 			power_group);

include/linux/usb.h

···
 
 	unsigned auto_pm:1;		/* autosuspend/resume in progress */
 	unsigned do_remote_wakeup:1;	/* remote wakeup should be enabled */
+	unsigned autosuspend_disabled:1; /* autosuspend and autoresume */
+	unsigned autoresume_disabled:1;  /*  disabled by the user */
 #endif
 };
 #define	to_usb_device(d) container_of(d, struct usb_device, dev)