USB: Export QUIRK_RESET_MORPHS through sysfs

Some devices which use mode switching revert to their
primary mode as they are reset. They must not be reset for
error handling. As user spaces makes the switch it also
has to tell the kernel that a device is quirky.

Signed-off-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Documentation/ABI/testing/sysfs-bus-usb

@@ -159,3 +159,14 @@ Description:
 		device.  This is useful to ensure auto probing won't
 		match the driver to the device.  For example:
 		# echo "046d c315" > /sys/bus/usb/drivers/foo/remove_id
+
+What:		/sys/bus/usb/device/.../avoid_reset
+Date:		December 2009
+Contact:	Oliver Neukum <oliver@neukum.org>
+Description:
+		Writing 1 to this file tells the kernel that this
+		device will morph into another mode when it is reset.
+		Drivers will not use reset for error handling for
+		such devices.
+Users:
+		usb_modeswitch

drivers/usb/core/sysfs.c

@@ -190,6 +190,36 @@ show_quirks(struct device *dev, struct device_attribute *attr, char *buf)
 }
 static DEVICE_ATTR(quirks, S_IRUGO, show_quirks, NULL);
 
+static ssize_t
+show_avoid_reset_quirk(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct usb_device *udev;
+
+	udev = to_usb_device(dev);
+	return sprintf(buf, "%d\n", !!(udev->quirks & USB_QUIRK_RESET_MORPHS));
+}
+
+static ssize_t
+set_avoid_reset_quirk(struct device *dev, struct device_attribute *attr,
+		const char *buf, size_t count)
+{
+	struct usb_device	*udev = to_usb_device(dev);
+	int			config;
+
+	if (sscanf(buf, "%d", &config) != 1 || config < 0 || config > 1)
+		return -EINVAL;
+	usb_lock_device(udev);
+	if (config)
+		udev->quirks |= USB_QUIRK_RESET_MORPHS;
+	else
+		udev->quirks &= ~USB_QUIRK_RESET_MORPHS;
+	usb_unlock_device(udev);
+	return count;
+}
+
+static DEVICE_ATTR(avoid_reset_quirk, S_IRUGO | S_IWUSR,
+		show_avoid_reset_quirk, set_avoid_reset_quirk);
+
 static ssize_t
 show_urbnum(struct device *dev, struct device_attribute *attr, char *buf)
 {
@@ -558,6 +588,7 @@ static struct attribute *dev_attrs[] = {
 	&dev_attr_version.attr,
 	&dev_attr_maxchild.attr,
 	&dev_attr_quirks.attr,
+	&dev_attr_avoid_reset_quirk.attr,
 	&dev_attr_authorized.attr,
 	&dev_attr_remove.attr,
 	NULL,