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Commit feccc30d authored by Alan Stern's avatar Alan Stern Committed by Greg Kroah-Hartman
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USB: remove CONFIG_USB_PERSIST setting 



This patch (as1047) removes the USB_PERSIST Kconfig option, enabling
it permanently.  It also prevents the power/persist attribute from
being created for hub devices; there's no point in having it since
USB-PERSIST is always turned on for hubs.

Signed-off-by: default avatarAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 5e6effae

Documentation/usb/persist.txt

+19 −16
Original line number Diff line number Diff line
@@ -2,7 +2,7 @@ 


		   Alan Stern <stern@rowland.harvard.edu>



		 September 2, 2006 (Updated May 29, 2007)

		September 2, 2006 (Updated February 25, 2008)





	What is the problem?
@@ -65,9 +65,10 @@ much better.) 


	What is the solution?



Setting CONFIG_USB_PERSIST will cause the kernel to work around these

issues.  It enables a mode in which the core USB device data

structures are allowed to persist across a power-session disruption.

The kernel includes a feature called USB-persist.  It tries to work

around these issues by allowing the core USB device data structures 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
@@ -80,28 +81,30 @@ 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.

unplugged.  The same thing happens if the host controller is in the

expected state but a USB device was unplugged and then replugged.



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

you would expect.  The kernel destroys the old device structure and

behaves as though the old device had been unplugged and a new device

plugged in, just as it would without the CONFIG_USB_PERSIST option.

plugged in.



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):

Note that the "USB-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.

automatically and permanently enabled and the power/persist file

doesn't even exist, so you only have to worry about setting it for

devices where it really matters.





	Is this the best solution?
@@ -112,19 +115,19 @@ centralized Logical Volume Manager. Such a solution would allow you 
to plug in a USB flash device, create a persistent volume associated

with it, unplug the flash device, plug it back in later, and still

have the same persistent volume associated with the device.  As such

it would be more far-reaching than CONFIG_USB_PERSIST.

it would be more far-reaching than USB-persist.



On the other hand, writing a persistent volume manager would be a big

job and using it would require significant input from the user.  This

solution is much quicker and easier -- and it exists now, a giant

point in its favor!



Furthermore, the USB_PERSIST option applies to _all_ USB devices, not

Furthermore, the USB-persist feature applies to _all_ USB devices, not

just mass-storage devices.  It might turn out to be equally useful for

other device types, such as network interfaces.





	WARNING: Using CONFIG_USB_PERSIST can be dangerous!!

	WARNING: USB-persist can be dangerous!!



When recovering an interrupted power session the kernel does its best

to make sure the USB device hasn't been changed; that is, the same
@@ -152,5 +155,5 @@ but yourself. 
YOU HAVE BEEN WARNED!  USE AT YOUR OWN RISK!



That having been said, most of the time there shouldn't be any trouble

at all.  The "persist" feature can be extremely useful.  Make the most

of it.
 
at all.  The USB-persist feature can be extremely useful.  Make the

most of it.

drivers/usb/core/Kconfig

+0 −25
Original line number Diff line number Diff line
@@ -102,31 +102,6 @@ config USB_SUSPEND 


	  If you are unsure about this, say N here.



config USB_PERSIST

	bool "USB device persistence during system suspend (DANGEROUS)"

	depends on USB && PM && EXPERIMENTAL

	default n

	help



	  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 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!



	  If a USB device is replaced by another of the same type while

	  the system is asleep, there's a good chance the kernel won't

	  detect the change.  Likewise if the media in a USB storage

	  device is replaced.  When this happens it's almost certain to

	  cause data corruption and maybe even crash your system.



	  If you are unsure, say N here.



config USB_OTG

	bool

	depends on USB && EXPERIMENTAL

drivers/usb/core/hub.c

+10 −17
Original line number Diff line number Diff line
@@ -30,12 +30,6 @@ 
#include "hcd.h"

#include "hub.h"



#ifdef	CONFIG_USB_PERSIST

#define	USB_PERSIST	1

#else

#define	USB_PERSIST	0

#endif



/* if we are in debug mode, always announce new devices */

#ifdef DEBUG

#ifndef CONFIG_USB_ANNOUNCE_NEW_DEVICES
@@ -695,7 +689,7 @@ static void hub_restart(struct usb_hub *hub, int type) 
		 * turn off the various status changes to prevent

		 * khubd from disconnecting it later.

		 */

		if (USB_PERSIST && udev->persist_enabled && status == 0 &&

		if (udev->persist_enabled && status == 0 &&

				!(portstatus & USB_PORT_STAT_ENABLE)) {

			if (portchange & USB_PORT_STAT_C_ENABLE)

				clear_port_feature(hub->hdev, port1,
@@ -1923,9 +1917,8 @@ static int finish_port_resume(struct usb_device *udev) 
 * the host and the device is the same as it was when the device

 * suspended.

 *

 * If CONFIG_USB_PERSIST and @udev->reset_resume are both set then this

 * routine won't check that the port is still enabled.  Furthermore,

 * if @udev->reset_resume is set then finish_port_resume() above will

 * If @udev->reset_resume is set then this routine won't check that the

 * port is still enabled.  Furthermore, finish_port_resume() above will

 * reset @udev.  The end result is that a broken power session can be

 * recovered and @udev will appear to persist across a loss of VBUS power.

 *
@@ -1937,8 +1930,8 @@ static int finish_port_resume(struct usb_device *udev) 
 * to it will be lost.  Using the USB_PERSIST facility, the device can be

 * made to appear as if it had not disconnected.

 *

 * This facility is inherently dangerous.  Although usb_reset_device()

 * makes every effort to insure that the same device is present after the

 * This facility can be dangerous.  Although usb_reset_device() makes

 * every effort to insure that the same device is present after the

 * reset as before, it cannot provide a 100% guarantee.  Furthermore it's

 * quite possible for a device to remain unaltered but its media to be

 * changed.  If the user replaces a flash memory card while the system is
@@ -1983,7 +1976,7 @@ int usb_port_resume(struct usb_device *udev) 
		status = hub_port_status(hub, port1, &portstatus, &portchange);



 SuspendCleared:

		if (USB_PERSIST && udev->reset_resume)

		if (udev->reset_resume)

			want_flags = USB_PORT_STAT_POWER

					| USB_PORT_STAT_CONNECTION;

		else
@@ -2113,10 +2106,10 @@ static int hub_reset_resume(struct usb_interface *intf) 
 *

 * The USB host controller driver calls this function when its root hub

 * is resumed and Vbus power has been interrupted or the controller

 * has been reset.  The routine marks @rhdev as having lost power.  When

 * the hub driver is resumed it will take notice; if CONFIG_USB_PERSIST

 * is enabled then it will carry out power-session recovery, otherwise

 * it will disconnect all the child devices.

 * has been reset.  The routine marks @rhdev as having lost power.

 * When the hub driver is resumed it will take notice and carry out

 * power-session recovery for all the "USB-PERSIST"-enabled child devices;

 * the others will be disconnected.

 */

void usb_root_hub_lost_power(struct usb_device *rhdev)

{

drivers/usb/core/quirks.c

+12 −0
Original line number Diff line number Diff line
@@ -97,4 +97,16 @@ void usb_detect_quirks(struct usb_device *udev) 
	if (udev->descriptor.bDeviceClass != USB_CLASS_HUB)

		udev->autosuspend_disabled = 1;

#endif



#ifdef	CONFIG_PM

	/* Hubs are automatically enabled for USB-PERSIST */

	if (udev->descriptor.bDeviceClass == USB_CLASS_HUB)

		udev->persist_enabled = 1;

#else

	/* In the absense of PM, we can safely enable USB-PERSIST

	 * for all devices.  It will affect things like hub resets

	 * and EMF-related port disables.

	 */

	udev->persist_enabled = 1;

#endif	/* CONFIG_PM */

}

drivers/usb/core/sysfs.c

+10 −12
Original line number Diff line number Diff line
@@ -180,11 +180,9 @@ show_urbnum(struct device *dev, struct device_attribute *attr, char *buf) 
static DEVICE_ATTR(urbnum, S_IRUGO, show_urbnum, NULL);





#if defined(CONFIG_USB_PERSIST) || defined(CONFIG_USB_SUSPEND)

static const char power_group[] = "power";

#endif

#ifdef	CONFIG_PM



#ifdef	CONFIG_USB_PERSIST

static const char power_group[] = "power";



static ssize_t

show_persist(struct device *dev, struct device_attribute *attr, char *buf)
@@ -222,9 +220,10 @@ static int add_persist_attributes(struct device *dev) 
	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;

		/* Hubs are automatically enabled for USB_PERSIST,

		 * no point in creating the attribute file.

		 */

		if (udev->descriptor.bDeviceClass != USB_CLASS_HUB)

			rc = sysfs_add_file_to_group(&dev->kobj,

					&dev_attr_persist.attr,

					power_group);
@@ -238,13 +237,12 @@ static void remove_persist_attributes(struct device *dev) 
			&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 */

#endif	/* CONFIG_PM */



#ifdef	CONFIG_USB_SUSPEND