diff options
Diffstat (limited to 'Documentation/usb/power-management.txt')
| -rw-r--r-- | Documentation/usb/power-management.txt | 15 |
1 files changed, 10 insertions, 5 deletions
diff --git a/Documentation/usb/power-management.txt b/Documentation/usb/power-management.txt index b2fc4d4a9917..e48ea1d51010 100644 --- a/Documentation/usb/power-management.txt +++ b/Documentation/usb/power-management.txt @@ -350,12 +350,12 @@ without holding the mutex. There also are a couple of utility routines drivers can use: - usb_autopm_enable() sets pm_usage_cnt to 1 and then calls - usb_autopm_set_interface(), which will attempt an autoresume. - - usb_autopm_disable() sets pm_usage_cnt to 0 and then calls + usb_autopm_enable() sets pm_usage_cnt to 0 and then calls usb_autopm_set_interface(), which will attempt an autosuspend. + usb_autopm_disable() sets pm_usage_cnt to 1 and then calls + usb_autopm_set_interface(), which will attempt an autoresume. + The conventional usage pattern is that a driver calls usb_autopm_get_interface() in its open routine and usb_autopm_put_interface() in its close or release routine. But @@ -436,7 +436,12 @@ post_reset; the USB core guarantees that this is true of internal suspend/resume events as well. If a driver wants to block all suspend/resume calls during some -critical section, it can simply acquire udev->pm_mutex. +critical section, it can simply acquire udev->pm_mutex. Note that +calls to resume may be triggered indirectly. Block IO due to memory +allocations can make the vm subsystem resume a device. Thus while +holding this lock you must not allocate memory with GFP_KERNEL or +GFP_NOFS. + Alternatively, if the critical section might call some of the usb_autopm_* routines, the driver can avoid deadlock by doing: |
