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List: linux-usb-devel
Subject: [linux-usb-devel] [PATCH 6/6] USB: add power/persist device
From: Alan Stern <stern () rowland ! harvard ! edu>
Date: 2007-05-30 19:39:33
Message-ID: Pine.LNX.4.44L0.0705301538590.2614-100000 () iolanthe ! rowland ! org
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This patch (as920) adds an extra level of protection to the
USB-Persist facility. Now it will apply by default only to hubs; for
all other devices the user must enable it explicitly by setting the
power/persist device attribute.
The disconnect_all_children() routine in hub.c has been removed and
its code placed inline. This is the way it was originally as part of
hub_pre_reset(); the revised usage in hub_reset_resume() is
sufficiently different that the code can no longer be shared.
Likewise, mark_children_for_reset() is now inline as part of
hub_reset_resume(). The end result looks much cleaner than before.
The sysfs interface is updated to add the new attribute file, and
there are corresponding documentation updates.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
---
Index: usb-2.6/include/linux/usb.h
===================================================================
--- usb-2.6.orig/include/linux/usb.h
+++ usb-2.6/include/linux/usb.h
@@ -404,6 +404,7 @@ struct usb_device {
unsigned auto_pm:1; /* autosuspend/resume in progress */
unsigned do_remote_wakeup:1; /* remote wakeup should be enabled */
unsigned reset_resume:1; /* needs reset instead of resume */
+ unsigned persist_enabled:1; /* USB_PERSIST enabled for this dev */
unsigned autosuspend_disabled:1; /* autosuspend and autoresume */
unsigned autoresume_disabled:1; /* disabled by the user */
#endif
Index: usb-2.6/drivers/usb/core/hub.c
===================================================================
--- usb-2.6.orig/drivers/usb/core/hub.c
+++ usb-2.6/drivers/usb/core/hub.c
@@ -596,27 +596,18 @@ static void hub_port_logical_disconnect(
kick_khubd(hub);
}
-static void disconnect_all_children(struct usb_hub *hub, int logical)
-{
- struct usb_device *hdev = hub->hdev;
- int port1;
-
- for (port1 = 1; port1 <= hdev->maxchild; ++port1) {
- if (hdev->children[port1-1]) {
- if (logical)
- hub_port_logical_disconnect(hub, port1);
- else
- usb_disconnect(&hdev->children[port1-1]);
- }
- }
-}
-
/* caller has locked the hub device */
static int hub_pre_reset(struct usb_interface *intf)
{
struct usb_hub *hub = usb_get_intfdata(intf);
+ struct usb_device *hdev = hub->hdev;
+ int i;
- disconnect_all_children(hub, 0);
+ /* Disconnect all the children */
+ for (i = 0; i < hdev->maxchild; ++i) {
+ if (hdev->children[i])
+ usb_disconnect(&hdev->children[i]);
+ }
hub_quiesce(hub);
return 0;
}
@@ -1872,51 +1863,41 @@ static int hub_resume(struct usb_interfa
return 0;
}
-#ifdef CONFIG_USB_PERSIST
-
-/* For "persistent-device" resets we must mark the child devices for reset
- * and turn off a possible connect-change status (so khubd won't disconnect
- * them later).
- */
-static void mark_children_for_reset_resume(struct usb_hub *hub)
+static int hub_reset_resume(struct usb_interface *intf)
{
+ struct usb_hub *hub = usb_get_intfdata(intf);
struct usb_device *hdev = hub->hdev;
int port1;
+ hub_power_on(hub);
+
for (port1 = 1; port1 <= hdev->maxchild; ++port1) {
struct usb_device *child = hdev->children[port1-1];
if (child) {
- child->reset_resume = 1;
- child->dev.power.prev_state.event = PM_EVENT_ON;
- clear_port_feature(hdev, port1,
- USB_PORT_FEAT_C_CONNECTION);
+
+ /* For "USB_PERSIST"-enabled children we must
+ * mark the child device for reset-resume and
+ * turn off the connect-change status to prevent
+ * khubd from disconnecting it later.
+ */
+ if (USB_PERSIST && child->persist_enabled) {
+ child->reset_resume = 1;
+ child->dev.power.prev_state.event =
+ PM_EVENT_ON;
+ clear_port_feature(hdev, port1,
+ USB_PORT_FEAT_C_CONNECTION);
+
+ /* Otherwise we must disconnect the child,
+ * but as we may not lock the child device here
+ * we have to do a "logical" disconnect.
+ */
+ } else {
+ hub_port_logical_disconnect(hub, port1);
+ }
}
}
-}
-#else
-
-static inline void mark_children_for_reset_resume(struct usb_hub *hub)
-{ }
-
-#endif /* CONFIG_USB_PERSIST */
-
-static int hub_reset_resume(struct usb_interface *intf)
-{
- struct usb_hub *hub = usb_get_intfdata(intf);
-
- hub_power_on(hub);
- if (USB_PERSIST)
- mark_children_for_reset_resume(hub);
- else {
- /* Reset-resume doesn't call pre_reset, so we have to
- * disconnect the children here. But we may not lock
- * the child devices, so we have to do a "logical"
- * disconnect.
- */
- disconnect_all_children(hub, 1);
- }
hub_activate(hub);
return 0;
}
Index: usb-2.6/drivers/usb/core/sysfs.c
===================================================================
--- usb-2.6.orig/drivers/usb/core/sysfs.c
+++ usb-2.6/drivers/usb/core/sysfs.c
@@ -169,6 +169,73 @@ show_quirks(struct device *dev, struct d
}
static DEVICE_ATTR(quirks, S_IRUGO, show_quirks, NULL);
+
+#if defined(CONFIG_USB_PERSIST) || defined(CONFIG_USB_SUSPEND)
+static const char power_group[] = "power";
+#endif
+
+#ifdef CONFIG_USB_PERSIST
+
+static ssize_t
+show_persist(struct device *dev, struct device_attribute *attr, char *buf)
+{
+ struct usb_device *udev = to_usb_device(dev);
+
+ return sprintf(buf, "%d\n", udev->persist_enabled);
+}
+
+static ssize_t
+set_persist(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct usb_device *udev = to_usb_device(dev);
+ int value;
+
+ /* Hubs are always enabled for USB_PERSIST */
+ if (udev->descriptor.bDeviceClass == USB_CLASS_HUB)
+ return -EPERM;
+
+ if (sscanf(buf, "%d", &value) != 1)
+ return -EINVAL;
+ usb_pm_lock(udev);
+ udev->persist_enabled = !!value;
+ usb_pm_unlock(udev);
+ return count;
+}
+
+static DEVICE_ATTR(persist, S_IRUGO | S_IWUSR, show_persist, set_persist);
+
+static int add_persist_attributes(struct device *dev)
+{
+ int rc = 0;
+
+ if (is_usb_device(dev)) {
+ struct usb_device *udev = to_usb_device(dev);
+
+ /* Hubs are automatically enabled for USB_PERSIST */
+ if (udev->descriptor.bDeviceClass == USB_CLASS_HUB)
+ udev->persist_enabled = 1;
+ rc = sysfs_add_file_to_group(&dev->kobj,
+ &dev_attr_persist.attr,
+ power_group);
+ }
+ return rc;
+}
+
+static void remove_persist_attributes(struct device *dev)
+{
+ sysfs_remove_file_from_group(&dev->kobj,
+ &dev_attr_persist.attr,
+ power_group);
+}
+
+#else
+
+#define add_persist_attributes(dev) 0
+#define remove_persist_attributes(dev) do {} while (0)
+
+#endif /* CONFIG_USB_PERSIST */
+
#ifdef CONFIG_USB_SUSPEND
static ssize_t
@@ -276,8 +343,6 @@ set_level(struct device *dev, struct dev
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;
@@ -311,6 +376,7 @@ static void remove_power_attributes(stru
#endif /* CONFIG_USB_SUSPEND */
+
/* Descriptor fields */
#define usb_descriptor_attr_le16(field, format_string) \
static ssize_t \
@@ -384,6 +450,10 @@ int usb_create_sysfs_dev_files(struct us
if (retval)
return retval;
+ retval = add_persist_attributes(dev);
+ if (retval)
+ goto error;
+
retval = add_power_attributes(dev);
if (retval)
goto error;
@@ -421,6 +491,7 @@ void usb_remove_sysfs_dev_files(struct u
device_remove_file(dev, &dev_attr_product);
device_remove_file(dev, &dev_attr_serial);
remove_power_attributes(dev);
+ remove_persist_attributes(dev);
sysfs_remove_group(&dev->kobj, &dev_attr_grp);
}
Index: usb-2.6/Documentation/ABI/testing/sysfs-bus-usb
===================================================================
--- usb-2.6.orig/Documentation/ABI/testing/sysfs-bus-usb
+++ usb-2.6/Documentation/ABI/testing/sysfs-bus-usb
@@ -39,3 +39,16 @@ Description:
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.
+
+What: /sys/bus/usb/devices/.../power/persist
+Date: May 2007
+KernelVersion: 2.6.23
+Contact: Alan Stern <stern@rowland.harvard.edu>
+Description:
+ If CONFIG_USB_PERSIST is set, then each USB device directory
+ will contain a file named power/persist. The file holds a
+ boolean value (0 or 1) indicating whether or not the
+ "USB-Persist" facility is enabled for the device. Since the
+ facility is inherently dangerous, it is disabled by default
+ for all devices except hubs. For more information, see
+ Documentation/usb/persist.txt.
Index: usb-2.6/Documentation/usb/persist.txt
===================================================================
--- usb-2.6.orig/Documentation/usb/persist.txt
+++ usb-2.6/Documentation/usb/persist.txt
@@ -2,7 +2,7 @@
Alan Stern <stern@rowland.harvard.edu>
- September 2, 2006 (Updated March 27, 2007)
+ September 2, 2006 (Updated May 29, 2007)
What is the problem?
@@ -52,9 +52,9 @@ you can convince the BIOS supplier to fi
On many systems the USB host controllers will get reset after a
suspend-to-RAM. On almost all systems, no suspend current is
-available during suspend-to-disk (also known as swsusp). You can
-check the kernel log after resuming to see if either of these has
-happened; look for lines saying "root hub lost power or was reset".
+available during hibernation (also known as swsusp or suspend-to-disk).
+You can check the kernel log after resuming to see if either of these
+has happened; look for lines saying "root hub lost power or was reset".
In practice, people are forced to unmount any filesystems on a USB
device before suspending. If the root filesystem is on a USB device,
@@ -71,15 +71,16 @@ structures are allowed to persist across
It works like this. If the kernel sees that a USB host controller is
not in the expected state during resume (i.e., if the controller was
reset or otherwise had lost power) then it applies a persistence check
-to each of the USB devices below that controller. It doesn't try to
-resume the device; that can't work once the power session is gone.
-Instead it issues a USB port reset and then re-enumerates the device.
-(This is exactly the same thing that happens whenever a USB device is
-reset.) If the re-enumeration shows that the device now attached to
-that port has the same descriptors as before, including the Vendor and
-Product IDs, then the kernel continues to use the same device
-structure. In effect, the kernel treats the device as though it had
-merely been reset instead of unplugged.
+to each of the USB devices below that controller for which the
+"persist" attribute is set. It doesn't try to resume the device; that
+can't work once the power session is gone. Instead it issues a USB
+port reset and then re-enumerates the device. (This is exactly the
+same thing that happens whenever a USB device is reset.) If the
+re-enumeration shows that the device now attached to that port has the
+same descriptors as before, including the Vendor and Product IDs, then
+the kernel continues to use the same device structure. In effect, the
+kernel treats the device as though it had merely been reset instead of
+unplugged.
If no device is now attached to the port, or if the descriptors are
different from what the kernel remembers, then the treatment is what
@@ -91,6 +92,17 @@ The end result is that the USB device re
Filesystem mounts and memory mappings are unaffected, and the world is
now a good and happy place.
+Note that even when CONFIG_USB_PERSIST is set, the "persist" feature
+will be applied only to those devices for which it is enabled. You
+can enable the feature by doing (as root):
+
+ echo 1 >/sys/bus/usb/devices/.../power/persist
+
+where the "..." should be filled in the with the device's ID. Disable
+the feature by writing 0 instead of 1. For hubs the feature is
+automatically and permanently enabled, so you only have to worry about
+setting it for devices where it really matters.
+
Is this the best solution?
Index: usb-2.6/drivers/usb/core/Kconfig
===================================================================
--- usb-2.6.orig/drivers/usb/core/Kconfig
+++ usb-2.6/drivers/usb/core/Kconfig
@@ -91,12 +91,15 @@ config USB_PERSIST
depends on USB && PM && EXPERIMENTAL
default n
help
- If you say Y here, USB device data structures will remain
+
+ If you say Y here and enable the "power/persist" attribute
+ for a USB device, the device's data structures will remain
persistent across system suspend, even if the USB bus loses
- power. (This includes software-suspend, also known as swsusp,
- or suspend-to-disk.) The devices will reappear as if by magic
- when the system wakes up, with no need to unmount USB filesystems,
- rmmod host-controller drivers, or do anything else.
+ power. (This includes hibernation, also known as swsusp or
+ suspend-to-disk.) The devices will reappear as if by magic
+ when the system wakes up, with no need to unmount USB
+ filesystems, rmmod host-controller drivers, or do anything
+ else.
WARNING: This option can be dangerous!
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