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authorIra Weiny <ira.weiny@intel.com>2021-12-02 07:42:59 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2021-12-03 18:41:50 +0300
commitb247703873c4d5088eee52d7902495b24967ce8e (patch)
tree1a8c964c46eb6f38711b0b13af8d830980f820e4 /Documentation/driver-api
parentf1045056c726440469d89d23c13734bcd6c0d15b (diff)
downloadlinux-b247703873c4d5088eee52d7902495b24967ce8e.tar.xz
Documentation/auxiliary_bus: Clarify auxiliary_device creation
The documentation for creating an auxiliary device is a 3 step not a 2 step process. Specifically the requirements of setting the name, id, dev.release, and dev.parent fields was not clear as a precursor to the '2 step' process documented. Clarify by declaring this a 3 step process starting with setting the fields of struct auxiliary_device correctly. Also add some sample code and tie the change into the rest of the documentation. Signed-off-by: Ira Weiny <ira.weiny@intel.com> Link: https://lore.kernel.org/r/20211202044305.4006853-2-ira.weiny@intel.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation/driver-api')
-rw-r--r--Documentation/driver-api/auxiliary_bus.rst81
1 files changed, 61 insertions, 20 deletions
diff --git a/Documentation/driver-api/auxiliary_bus.rst b/Documentation/driver-api/auxiliary_bus.rst
index ef902daf0d68..7dbb4f16462a 100644
--- a/Documentation/driver-api/auxiliary_bus.rst
+++ b/Documentation/driver-api/auxiliary_bus.rst
@@ -71,26 +71,14 @@ they are not physical devices that are controlled by DT/ACPI. The same
argument applies for not using MFD in this scenario as MFD relies on individual
function devices being physical devices.
-Auxiliary Device
-================
+Auxiliary Device Creation
+=========================
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.
-Registering an auxiliary_device is a two-step process. First 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 second step in registering an auxiliary_device is to perform a call to
-auxiliary_device_add(), which sets the name of the device and add the device to
-the bus.
-
-Unregistering an auxiliary_device is also a two-step process to mirror the
-register process. First call auxiliary_device_delete(), then call
-auxiliary_device_uninit().
-
.. code-block:: c
struct auxiliary_device {
@@ -99,15 +87,68 @@ auxiliary_device_uninit().
u32 id;
};
-If two auxiliary_devices both with a match_name "mod.foo" are registered onto
-the bus, they must have unique id values (e.g. "x" and "y") so that the
-registered devices names are "mod.foo.x" and "mod.foo.y". If match_name + id
-are not unique, then the device_add fails and generates an error message.
+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
+"mod.MY_DEVICE_NAME", are registered onto the bus, they must have unique id
+values (e.g. "x" and "y") so that the registered devices names are "mod.foo.x"
+and "mod.foo.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.
+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
+
+ 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);
-The auxiliary_device.dev.parent must also be populated.
Auxiliary Device Memory Model and Lifespan
------------------------------------------