xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

USB: remove CONFIG_USB_PERSIST setting

Browse Source 
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: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Alan Stern
2008-03-03 15:15:59 -05:00
committed by Greg Kroah-Hartman
parent 5e6effaed6
commit feccc30d90
7 changed files with 53 additions and 81 deletions
Download Patch File Download Diff File Expand all files Collapse all files

35
Documentation/usb/persist.txt
View File

@@ -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.