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driver core: Add state_synced sysfs file for devices that support it 

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 <saravanak@google.com>
Link: https://lore.kernel.org/r/20200521191800.136035-3-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Saravana Kannan 2020-05-21 12:17:59 -07:00 committed by Greg Kroah-Hartman
parent 287905e68d
commit 8fd456ec0c
2 changed files with 46 additions and 0 deletions
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24
Documentation/ABI/testing/sysfs-devices-state_synced Normal file
View File

@ -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.

22
drivers/base/dd.c
View File

@ -462,6 +462,18 @@ 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)
{
bool val;
device_lock(dev);
val = dev->state_synced;
device_unlock(dev);
return sprintf(buf, "%u\n", val);
}
static DEVICE_ATTR_RO(state_synced);
static int really_probe(struct device *dev, struct device_driver *drv)
{
int ret = -EPROBE_DEFER;
@ -535,9 +547,16 @@ re_probe:
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)
@ -567,6 +586,8 @@ re_probe:
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);
@ -1104,6 +1125,7 @@ static void __device_release_driver(struct device *dev, struct device *parent)
pm_runtime_put_sync(dev);
device_remove_file(dev, &dev_attr_state_synced);
device_remove_groups(dev, drv->dev_groups);
if (dev->bus && dev->bus->remove)