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| author | Mauro Carvalho Chehab <mchehab@s-opensource.com> | 2017-04-05 15:23:09 +0200 |
|---|---|---|
| committer | Jonathan Corbet <corbet@lwn.net> | 2017-04-11 22:40:12 +0200 |
| commit | 32a3bebce9d09598d4f4c5afca929a2ce148b8c4 (patch) | |
| tree | a0ac3c5bddc53cc9a21575274a9711a29b4af796 | |
| parent | usb/hotplug.txt: convert to ReST and add to driver-api book (diff) | |
| download | linux-32a3bebce9d09598d4f4c5afca929a2ce148b8c4.tar.xz linux-32a3bebce9d09598d4f4c5afca929a2ce148b8c4.zip | |
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>
| -rw-r--r-- | Documentation/driver-api/usb/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/driver-api/usb/persist.rst (renamed from Documentation/usb/persist.txt) | 22 |
2 files changed, 14 insertions, 9 deletions
diff --git a/Documentation/driver-api/usb/index.rst b/Documentation/driver-api/usb/index.rst index 43f0a8b72b11..3f08cb5d5feb 100644 --- a/Documentation/driver-api/usb/index.rst +++ b/Documentation/driver-api/usb/index.rst @@ -12,6 +12,7 @@ Linux USB API dma power-management hotplug + persist error-codes writing_usb_driver writing_musb_glue_layer diff --git a/Documentation/usb/persist.txt b/Documentation/driver-api/usb/persist.rst index 35d70eda9ad6..ea1b43f0559e 100644 --- a/Documentation/usb/persist.txt +++ b/Documentation/driver-api/usb/persist.rst @@ -1,11 +1,12 @@ - USB device persistence during system suspend +USB device persistence during system suspend +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - Alan Stern <stern@rowland.harvard.edu> +:Author: Alan Stern <stern@rowland.harvard.edu> +:Date: September 2, 2006 (Updated February 25, 2008) - 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 |