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driver core: Add deferred_probe attribute to devices in sysfs 

It is sometimes useful to know that a device is on the deferred probe
list rather than, say, not having a driver available.  Expose this
information to user-space.

Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ben Hutchings 2016-08-16 14:34:18 +01:00 committed by Greg Kroah-Hartman
parent baa8809f60
commit 6751667a29
4 changed files with 34 additions and 0 deletions
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12
Documentation/ABI/testing/sysfs-devices-deferred_probe Normal file
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@ -0,0 +1,12 @@
What: /sys/devices/.../deferred_probe
Date: August 2016
Contact: Ben Hutchings <ben.hutchings@codethink.co.uk>
Description:
The /sys/devices/.../deferred_probe attribute is
present for all devices. If a driver detects during
probing a device that a related device is not yet
ready, it may defer probing of the first device. The
kernel will retry probing the first device after any
other device is successfully probed. This attribute
reads as 1 if probing of this device is currently
deferred, or 0 otherwise.

2
drivers/base/base.h
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@ -141,6 +141,8 @@ extern void device_unblock_probing(void);
extern struct kset *devices_kset;
extern void devices_kset_move_last(struct device *dev);
extern struct device_attribute dev_attr_deferred_probe;
#if defined(CONFIG_MODULES) && defined(CONFIG_SYSFS)
extern void module_add_driver(struct module *mod, struct device_driver *drv);
extern void module_remove_driver(struct device_driver *drv);

7
drivers/base/core.c
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@ -1060,8 +1060,14 @@ static int device_add_attrs(struct device *dev)
goto err_remove_dev_groups;
}
error = device_create_file(dev, &dev_attr_deferred_probe);
if (error)
goto err_remove_online;
return 0;
err_remove_online:
device_remove_file(dev, &dev_attr_online);
err_remove_dev_groups:
device_remove_groups(dev, dev->groups);
err_remove_type_groups:
@ -1079,6 +1085,7 @@ static void device_remove_attrs(struct device *dev)
struct class *class = dev->class;
const struct device_type *type = dev->type;
device_remove_file(dev, &dev_attr_deferred_probe);
device_remove_file(dev, &dev_attr_online);
device_remove_groups(dev, dev->groups);

13
drivers/base/dd.c
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@ -53,6 +53,19 @@ static LIST_HEAD(deferred_probe_pending_list);
static LIST_HEAD(deferred_probe_active_list);
static atomic_t deferred_trigger_count = ATOMIC_INIT(0);
static ssize_t deferred_probe_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
bool value;
mutex_lock(&deferred_probe_mutex);
value = !list_empty(&dev->p->deferred_probe);
mutex_unlock(&deferred_probe_mutex);
return sprintf(buf, "%d\n", value);
}
DEVICE_ATTR_RO(deferred_probe);
/*
* In some cases, like suspend to RAM or hibernation, It might be reasonable
* to prohibit probing of devices as it could be unsafe.