Documentation/auxiliary_bus: Move the text into the code

The code and documentation are more difficult to maintain when kept
separately.  This is further compounded when the standard structure
documentation infrastructure is not used.

Move the documentation into the code, use the standard documentation
infrastructure, add current documented functions, and reference the text
in the rst file.

Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/20211202044305.4006853-8-ira.weiny@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 160 insertions, 0 deletions

diff --git a/include/linux/auxiliary_bus.h b/include/linux/auxiliary_bus.h
index 605b27aab693..e6d8b5c16226 100644
--- a/include/linux/auxiliary_bus.h
+++ b/include/linux/auxiliary_bus.h
@@ -11,12 +11,172 @@
 #include <linux/device.h>
 #include <linux/mod_devicetable.h>
 
+/**
+ * DOC: DEVICE_LIFESPAN
+ *
+ * The registering driver is the entity that allocates memory for the
+ * auxiliary_device and registers it on the auxiliary bus.  It is important to
+ * note that, as opposed to the platform bus, the registering driver is wholly
+ * responsible for the management of the memory used for the device object.
+ *
+ * To be clear the memory for the auxiliary_device is freed in the release()
+ * callback defined by the registering driver.  The registering driver should
+ * only call auxiliary_device_delete() and then auxiliary_device_uninit() when
+ * it is done with the device.  The release() function is then automatically
+ * called if and when other code releases their reference to the devices.
+ *
+ * A parent object, defined in the shared header file, contains the
+ * auxiliary_device.  It also contains a pointer to the shared object(s), which
+ * also is defined in the shared header.  Both the parent object and the shared
+ * object(s) are allocated by the registering driver.  This layout allows the
+ * auxiliary_driver's registering module to perform a container_of() call to go
+ * from the pointer to the auxiliary_device, that is passed during the call to
+ * the auxiliary_driver's probe function, up to the parent object, and then
+ * have access to the shared object(s).
+ *
+ * The memory for the shared object(s) must have a lifespan equal to, or
+ * greater than, the lifespan of the memory for the auxiliary_device.  The
+ * auxiliary_driver should only consider that the shared object is valid as
+ * long as the auxiliary_device is still registered on the auxiliary bus.  It
+ * is up to the registering driver to manage (e.g. free or keep available) the
+ * memory for the shared object beyond the life of the auxiliary_device.
+ *
+ * The registering driver must unregister all auxiliary devices before its own
+ * driver.remove() is completed.  An easy way to ensure this is to use the
+ * devm_add_action_or_reset() call to register a function against the parent
+ * device which unregisters the auxiliary device object(s).
+ *
+ * Finally, any operations which operate on the auxiliary devices must continue
+ * to function (if only to return an error) after the registering driver
+ * unregisters the auxiliary device.
+ */
+
+/**
+ * struct auxiliary_device - auxiliary device object.
+ * @dev: Device,
+ *       The release and parent fields of the device structure must be filled
+ *       in
+ * @name: Match name found by the auxiliary device driver,
+ * @id: unique identitier if multiple devices of the same name are exported,
+ *
+ * An auxiliary_device represents a part of its parent device's functionality.
+ * It is given a name that, combined with the registering drivers
+ * KBUILD_MODNAME, creates a match_name that is used for driver binding, and an
+ * id that combined with the match_name provide a unique name to register with
+ * the bus subsystem.  For example, a driver registering an auxiliary device is
+ * named 'foo_mod.ko' and the subdevice is named 'foo_dev'.  The match name is
+ * therefore 'foo_mod.foo_dev'.
+ *
+ * Registering an auxiliary_device is a three-step process.
+ *
+ * First, a 'struct auxiliary_device' needs to be defined or allocated for each
+ * sub-device desired.  The name, id, dev.release, and dev.parent fields of
+ * this structure must be filled in as follows.
+ *
+ * The 'name' field is to be given a name that is recognized by the auxiliary
+ * driver.  If two auxiliary_devices with the same match_name, eg
+ * "foo_mod.foo_dev", are registered onto the bus, they must have unique id
+ * values (e.g. "x" and "y") so that the registered devices names are
+ * "foo_mod.foo_dev.x" and "foo_mod.foo_dev.y".  If match_name + id are not
+ * unique, then the device_add fails and generates an error message.
+ *
+ * The auxiliary_device.dev.type.release or auxiliary_device.dev.release must
+ * be populated with a non-NULL pointer to successfully register the
+ * auxiliary_device.  This release call is where resources associated with the
+ * auxiliary device must be free'ed.  Because once the device is placed on the
+ * bus the parent driver can not tell what other code may have a reference to
+ * this data.
+ *
+ * The auxiliary_device.dev.parent should be set.  Typically to the registering
+ * drivers device.
+ *
+ * Second, call auxiliary_device_init(), which checks several aspects of the
+ * auxiliary_device struct and performs a device_initialize().  After this step
+ * completes, any error state must have a call to auxiliary_device_uninit() in
+ * its resolution path.
+ *
+ * The third and final step in registering an auxiliary_device is to perform a
+ * call to auxiliary_device_add(), which sets the name of the device and adds
+ * the device to the bus.
+ *
+ * .. code-block:: c
+ *
+ *      #define MY_DEVICE_NAME "foo_dev"
+ *
+ *      ...
+ *
+ *	struct auxiliary_device *my_aux_dev = my_aux_dev_alloc(xxx);
+ *
+ *	// Step 1:
+ *	my_aux_dev->name = MY_DEVICE_NAME;
+ *	my_aux_dev->id = my_unique_id_alloc(xxx);
+ *	my_aux_dev->dev.release = my_aux_dev_release;
+ *	my_aux_dev->dev.parent = my_dev;
+ *
+ *	// Step 2:
+ *	if (auxiliary_device_init(my_aux_dev))
+ *		goto fail;
+ *
+ *	// Step 3:
+ *	if (auxiliary_device_add(my_aux_dev)) {
+ *		auxiliary_device_uninit(my_aux_dev);
+ *		goto fail;
+ *	}
+ *
+ *	...
+ *
+ *
+ * Unregistering an auxiliary_device is a two-step process to mirror the
+ * register process.  First call auxiliary_device_delete(), then call
+ * auxiliary_device_uninit().
+ *
+ * .. code-block:: c
+ *
+ *         auxiliary_device_delete(my_dev->my_aux_dev);
+ *         auxiliary_device_uninit(my_dev->my_aux_dev);
+ */
 struct auxiliary_device {
 	struct device dev;
 	const char *name;
 	u32 id;
 };
 
+/**
+ * struct auxiliary_driver - Definition of an auxiliary bus driver
+ * @probe: Called when a matching device is added to the bus.
+ * @remove: Called when device is removed from the bus.
+ * @shutdown: Called at shut-down time to quiesce the device.
+ * @suspend: Called to put the device to sleep mode. Usually to a power state.
+ * @resume: Called to bring a device from sleep mode.
+ * @name: Driver name.
+ * @driver: Core driver structure.
+ * @id_table: Table of devices this driver should match on the bus.
+ *
+ * Auxiliary drivers follow the standard driver model convention, where
+ * discovery/enumeration is handled by the core, and drivers provide probe()
+ * and remove() methods. They support power management and shutdown
+ * notifications using the standard conventions.
+ *
+ * Auxiliary drivers register themselves with the bus by calling
+ * auxiliary_driver_register(). The id_table contains the match_names of
+ * auxiliary devices that a driver can bind with.
+ *
+ * .. code-block:: c
+ *
+ *         static const struct auxiliary_device_id my_auxiliary_id_table[] = {
+ *		   { .name = "foo_mod.foo_dev" },
+ *                 {},
+ *         };
+ *
+ *         MODULE_DEVICE_TABLE(auxiliary, my_auxiliary_id_table);
+ *
+ *         struct auxiliary_driver my_drv = {
+ *                 .name = "myauxiliarydrv",
+ *                 .id_table = my_auxiliary_id_table,
+ *                 .probe = my_drv_probe,
+ *                 .remove = my_drv_remove
+ *         };
+ */
 struct auxiliary_driver {
 	int (*probe)(struct auxiliary_device *auxdev, const struct auxiliary_device_id *id);
 	void (*remove)(struct auxiliary_device *auxdev);