This can be used to check if a device supports sync_state() callbacks
and therefore keeps resources left on by the bootloader enabled till all
its consumers have probed.
This can also be used to check if sync_state() has been called for a
device or whether it is still trying to keep resources enabled because
they were left enabled by the bootloader and all its consumers haven't
probed yet.
Signed-off-by: Saravana Kannan <sarava...@google.com>
---
.../ABI/testing/sysfs-devices-state_synced | 24 +++++++++++++++++++
drivers/base/dd.c | 16 +++++++++++++
2 files changed, 40 insertions(+)
create mode 100644 Documentation/ABI/testing/sysfs-devices-state_synced
diff --git a/Documentation/ABI/testing/sysfs-devices-state_synced
b/Documentation/ABI/testing/sysfs-devices-state_synced
new file mode 100644
index 000000000000..0c922d7d02fc
--- /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 <sarava...@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.
+
+
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 48ca81cb8ebc..72599436ae84 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -458,6 +458,13 @@ static void driver_deferred_probe_add_trigger(struct
device *dev,
driver_deferred_probe_trigger();
}
+static ssize_t state_synced_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ return sprintf(buf, "%u\n", dev->state_synced);
+}
+static DEVICE_ATTR_RO(state_synced);
+
static int really_probe(struct device *dev, struct device_driver *drv)
{
int ret = -EPROBE_DEFER;
@@ -531,9 +538,16 @@ static int really_probe(struct device *dev, struct
device_driver *drv)
goto dev_groups_failed;
}
+ if (dev_has_sync_state(dev) &&
+ device_create_file(dev, &dev_attr_state_synced)) {
+ dev_err(dev, "state_synced sysfs add failed\n");
+ goto dev_sysfs_state_synced_failed;
+ }
+
if (test_remove) {
test_remove = false;
+ device_remove_file(dev, &dev_attr_state_synced);
device_remove_groups(dev, drv->dev_groups);
if (dev->bus->remove)
@@ -563,6 +577,8 @@ static int really_probe(struct device *dev, struct
device_driver *drv)
drv->bus->name, __func__, dev_name(dev), drv->name);
goto done;
+dev_sysfs_state_synced_failed:
+ device_remove_groups(dev, drv->dev_groups);
dev_groups_failed:
if (dev->bus->remove)
dev->bus->remove(dev);
--
2.26.2.645.ge9eca65c58-goog
