driver-core: add asynchronous probing support for drivers

Some devices take a long time when initializing, and not all drivers are
suited to initialize their devices when they are open. For example,
input drivers need to interrogate their devices in order to publish
device's capabilities before userspace will open them. When such drivers
are compiled into kernel they may stall entire kernel initialization.

This change allows drivers request for their probe functions to be
called asynchronously during driver and device registration (manual
binding is still synchronous). Because async_schedule is used to perform
asynchronous calls module loading will still wait for the probing to
complete.

Note that the end goal is to make the probing asynchronous by default,
so annotating drivers with PROBE_PREFER_ASYNCHRONOUS is a temporary
measure that allows us to speed up boot process while we validating and
fixing the rest of the drivers and preparing userspace.

This change is based on earlier patch by "Luis R. Rodriguez"
<mcgrof@suse.com>

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 28 insertions, 0 deletions

diff --git a/include/linux/device.h b/include/linux/device.h
index 6558af90c8fe..7857b46c548b 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -196,12 +196,38 @@ extern struct kset *bus_get_kset(struct bus_type *bus);
 extern struct klist *bus_get_device_klist(struct bus_type *bus);
 
 /**
+ * enum probe_type - device driver probe type to try
+ *	Device drivers may opt in for special handling of their
+ *	respective probe routines. This tells the core what to
+ *	expect and prefer.
+ *
+ * @PROBE_SYNCHRONOUS: Default. Drivers expect their probe routines
+ *	to run synchronously with driver and device registration
+ *	(with the exception of -EPROBE_DEFER handling - re-probing
+ *	always ends up being done asynchronously).
+ * @PROBE_PREFER_ASYNCHRONOUS: Drivers for "slow" devices which
+ *	probing order is not essential for booting the system may
+ *	opt into executing their probes asynchronously.
+ *
+ * Note that the end goal is to switch the kernel to use asynchronous
+ * probing by default, so annotating drivers with
+ * %PROBE_PREFER_ASYNCHRONOUS is a temporary measure that allows us
+ * to speed up boot process while we are validating the rest of the
+ * drivers.
+ */
+enum probe_type {
+	PROBE_SYNCHRONOUS,
+	PROBE_PREFER_ASYNCHRONOUS,
+};
+
+/**
  * struct device_driver - The basic device driver structure
  * @name:	Name of the device driver.
  * @bus:	The bus which the device of this driver belongs to.
  * @owner:	The module owner.
  * @mod_name:	Used for built-in modules.
  * @suppress_bind_attrs: Disables bind/unbind via sysfs.
+ * @probe_type:	Type of the probe (synchronous or asynchronous) to use.
  * @of_match_table: The open firmware table.
  * @acpi_match_table: The ACPI match table.
  * @probe:	Called to query the existence of a specific device,
@@ -235,6 +261,7 @@ struct device_driver {
 	const char		*mod_name;	/* used for built-in modules */
 
 	bool suppress_bind_attrs;	/* disables bind/unbind via sysfs */
+	enum probe_type probe_type;
 
 	const struct of_device_id	*of_match_table;
 	const struct acpi_device_id	*acpi_match_table;
@@ -975,6 +1002,7 @@ extern int __must_check device_bind_driver(struct device *dev);
 extern void device_release_driver(struct device *dev);
 extern int  __must_check device_attach(struct device *dev);
 extern int __must_check driver_attach(struct device_driver *drv);
+extern void device_initial_probe(struct device *dev);
 extern int __must_check device_reprobe(struct device *dev);
 
 /*