From b247703873c4d5088eee52d7902495b24967ce8e Mon Sep 17 00:00:00 2001 From: Ira Weiny Date: Wed, 1 Dec 2021 20:42:59 -0800 Subject: [PATCH] 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 Link: https://lore.kernel.org/r/20211202044305.4006853-2-ira.weiny@intel.com Signed-off-by: Greg Kroah-Hartman --- Documentation/driver-api/auxiliary_bus.rst | 81 ++++++++++++++++------ drivers/base/auxiliary.c | 4 +- 2 files changed, 63 insertions(+), 22 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 ------------------------------------------ diff --git a/drivers/base/auxiliary.c b/drivers/base/auxiliary.c index 9230c9472bb0..70a8dbcd31b7 100644 --- a/drivers/base/auxiliary.c +++ b/drivers/base/auxiliary.c @@ -117,7 +117,7 @@ static struct bus_type auxiliary_bus_type = { * auxiliary_device_init - check auxiliary_device and initialize * @auxdev: auxiliary device struct * - * This is the first step in the two-step process to register an + * This is the second step in the three-step process to register an * auxiliary_device. * * When this function returns an error code, then the device_initialize will @@ -155,7 +155,7 @@ EXPORT_SYMBOL_GPL(auxiliary_device_init); * @auxdev: auxiliary bus device to add to the bus * @modname: name of the parent device's driver module * - * This is the second step in the two-step process to register an + * This is the third step in the three-step process to register an * auxiliary_device. * * This function must be called after a successful call to