summaryrefslogtreecommitdiffstats
path: root/Documentation/ABI/testing/sysfs-devices-state_synced
diff options
context:
space:
mode:
Diffstat (limited to '')
-rw-r--r--Documentation/ABI/testing/sysfs-devices-state_synced24
1 files changed, 24 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-devices-state_synced b/Documentation/ABI/testing/sysfs-devices-state_synced
new file mode 100644
index 000000000..0c922d7d0
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-state_synced
@@ -0,0 +1,24 @@
+What: /sys/devices/.../state_synced
+Date: May 2020
+Contact: Saravana Kannan <saravanak@google.com>
+Description:
+ The /sys/devices/.../state_synced attribute is only present for
+ devices whose bus types or driver provides the .sync_state()
+ callback. The number read from it (0 or 1) reflects the value
+ of the device's 'state_synced' field. A value of 0 means the
+ .sync_state() callback hasn't been called yet. A value of 1
+ means the .sync_state() callback has been called.
+
+ Generally, if a device has sync_state() support and has some of
+ the resources it provides enabled at the time the kernel starts
+ (Eg: enabled by hardware reset or bootloader or anything that
+ run before the kernel starts), then it'll keep those resources
+ enabled and in a state that's compatible with the state they
+ were in at the start of the kernel. The device will stop doing
+ this only when the sync_state() callback has been called --
+ which happens only when all its consumer devices are registered
+ and have probed successfully. Resources that were left disabled
+ at the time the kernel starts are not affected or limited in
+ any way by sync_state() callbacks.
+
+