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USB: add power/persist device attribute 

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Alan Stern 2007-05-30 15:39:33 -04:00 committed by Greg Kroah-Hartman
parent 54515fe528
commit b41a60eca8
6 changed files with 149 additions and 69 deletions
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13
Documentation/ABI/testing/sysfs-bus-usb
View File

@ -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.

38
Documentation/usb/persist.txt
View File

@ -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 fix the problem (lots of luck!).
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 a power-session disruption.
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 remains available and usable.
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?

13
drivers/usb/core/Kconfig
View File

@ -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!

78
drivers/usb/core/hub.c
View File

@ -596,27 +596,18 @@ static void hub_port_logical_disconnect(struct usb_hub *hub, int port1)
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;
}
@ -1872,50 +1863,39 @@ static int hub_resume(struct usb_interface *intf)
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;
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;
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;
}

75
drivers/usb/core/sysfs.c
View File

@ -169,6 +169,73 @@ show_quirks(struct device *dev, struct device_attribute *attr, char *buf)
}
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 device_attribute *attr,
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(struct device *dev)
#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 usb_device *udev)
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 usb_device *udev)
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);
}

1
include/linux/usb.h
View File

@ -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