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authorAlan Stern <stern@rowland.harvard.edu>2007-11-16 11:58:15 -0500
committerGreg Kroah-Hartman <gregkh@suse.de>2007-11-28 13:58:34 -0800
commit3c886c50486cfbef2a2382b99bf4083a465c970a (patch)
treee7482b8fd40791db70d1b241ec23d0cd6267c401
parentbc59462b80c694670fbb5d0bb1a8450ffc353080 (diff)
USB: power-management documenation update
This patch (as1014) was partly written by Tilman Schmidt. It clarifies the USB power-management documentation by explaining that when a disconnect occurs, a suspend method call might not be followed by either a resume or a reset_resume call. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Tilman Schmidt <tilman@imap.cc> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--Documentation/usb/power-management.txt8
1 files changed, 8 insertions, 0 deletions
diff --git a/Documentation/usb/power-management.txt b/Documentation/usb/power-management.txt
index 97842deec471..b2fc4d4a9917 100644
--- a/Documentation/usb/power-management.txt
+++ b/Documentation/usb/power-management.txt
@@ -278,6 +278,14 @@ optional. The methods' jobs are quite simple:
(although the interfaces will be in the same altsettings as
before the suspend).
+If the device is disconnected or powered down while it is suspended,
+the disconnect method will be called instead of the resume or
+reset_resume method. This is also quite likely to happen when
+waking up from hibernation, as many systems do not maintain suspend
+current to the USB host controllers during hibernation. (It's
+possible to work around the hibernation-forces-disconnect problem by
+using the USB Persist facility.)
+
The reset_resume method is used by the USB Persist facility (see
Documentation/usb/persist.txt) and it can also be used under certain
circumstances when CONFIG_USB_PERSIST is not enabled. Currently, if a