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usb/persist.txt: convert to ReST and add to driver-api book 

This document describe some USB core features. Add it to the
driver-api book.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mauro Carvalho Chehab 2017-04-05 10:23:09 -03:00 committed by Jonathan Corbet
parent 76f650f077
commit 32a3bebce9
2 changed files with 14 additions and 9 deletions
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1
Documentation/driver-api/usb/index.rst
View File

@ -12,6 +12,7 @@ Linux USB API
dma
power-management
hotplug
persist
error-codes
writing_usb_driver
writing_musb_glue_layer

22
Documentation/usb/persist.txt → Documentation/driver-api/usb/persist.rst
View File

@ -1,11 +1,12 @@
USB device persistence during system suspend
USB device persistence during system suspend
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Alan Stern <stern@rowland.harvard.edu>
September 2, 2006 (Updated February 25, 2008)
:Author: Alan Stern <stern@rowland.harvard.edu>
:Date: September 2, 2006 (Updated February 25, 2008)
What is the problem?
What is the problem?
====================
According to the USB specification, when a USB bus is suspended the
bus must continue to supply suspend current (around 1-5 mA). This
@ -63,7 +64,8 @@ suspended -- but it will crash as soon as it wakes up, which isn't
much better.)
What is the solution?
What is the solution?
=====================
The kernel includes a feature called USB-persist. It tries to work
around these issues by allowing the core USB device data structures to
@ -99,7 +101,7 @@ now a good and happy place.
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):
(as root)::
echo 1 >/sys/bus/usb/devices/.../power/persist
@ -110,7 +112,8 @@ doesn't even exist, so you only have to worry about setting it for
devices where it really matters.
Is this the best solution?
Is this the best solution?
==========================
Perhaps not. Arguably, keeping track of mounted filesystems and
memory mappings across device disconnects should be handled by a
@ -130,7 +133,8 @@ just mass-storage devices. It might turn out to be equally useful for
other device types, such as network interfaces.
WARNING: 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