Signed-off-by: Dave Young <[email protected]>
---
Documentation/usb/power-management.txt | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff -upr linux/Documentation/usb/power-management.txt linux.new/Documentation/usb/power-management.txt
--- linux/Documentation/usb/power-management.txt 2007-12-28 09:55:07.000000000 +0800
+++ linux.new/Documentation/usb/power-management.txt 2007-12-28 09:58:57.000000000 +0800
@@ -429,8 +429,8 @@ interface.
All three suspend/resume methods are always called while holding the
usb_device's PM mutex. For external events -- but not necessarily for
-autosuspend or autoresume -- the device semaphore (udev->dev.sem) will
-also be held. This implies that external suspend/resume events are
+autosuspend or autoresume -- the device mutex (udev->dev.mutex) will
+also be locked. This implies that external suspend/resume events are
mutually exclusive with calls to probe, disconnect, pre_reset, and
post_reset; the USB core guarantees that this is true of internal
suspend/resume events as well.
@@ -440,29 +440,29 @@ critical section, it can simply acquire
Alternatively, if the critical section might call some of the
usb_autopm_* routines, the driver can avoid deadlock by doing:
- down(&udev->dev.sem);
+ mutex_lock(&udev->dev.mutex);
rc = usb_autopm_get_interface(intf);
and at the end of the critical section:
if (!rc)
usb_autopm_put_interface(intf);
- up(&udev->dev.sem);
+ mutex_unlock(&udev->dev.mutex);
-Holding the device semaphore will block all external PM calls, and the
+Lock the device mutex will block all external PM calls, and the
usb_autopm_get_interface() will prevent any internal PM calls, even if
it fails. (Exercise: Why?)
The rules for locking order are:
- Never acquire any device semaphore while holding any PM mutex.
+ Never acquire any device mutex while holding any PM mutex.
Never acquire udev->pm_mutex while holding the PM mutex for
a device that isn't a descendant of udev.
In other words, PM mutexes should only be acquired going up the device
tree, and they should be acquired only after locking all the device
-semaphores you need to hold. These rules don't matter to drivers very
+mutexes. These rules don't matter to drivers very
much; they usually affect just the USB core.
Still, drivers do need to be careful. For example, many drivers use a
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