// SPDX-License-Identifier: GPL-2.0-only /* * Copyright (c) 2019-2020 Intel Corporation * * Please see Documentation/driver-api/auxiliary_bus.rst for more information. */ #define pr_fmt(fmt) … #include <linux/device.h> #include <linux/init.h> #include <linux/slab.h> #include <linux/module.h> #include <linux/pm_domain.h> #include <linux/pm_runtime.h> #include <linux/string.h> #include <linux/auxiliary_bus.h> #include "base.h" /** * DOC: PURPOSE * * In some subsystems, the functionality of the core device (PCI/ACPI/other) is * too complex for a single device to be managed by a monolithic driver (e.g. * Sound Open Firmware), multiple devices might implement a common intersection * of functionality (e.g. NICs + RDMA), or a driver may want to export an * interface for another subsystem to drive (e.g. SIOV Physical Function export * Virtual Function management). A split of the functionality into child- * devices representing sub-domains of functionality makes it possible to * compartmentalize, layer, and distribute domain-specific concerns via a Linux * device-driver model. * * An example for this kind of requirement is the audio subsystem where a * single IP is handling multiple entities such as HDMI, Soundwire, local * devices such as mics/speakers etc. The split for the core's functionality * can be arbitrary or be defined by the DSP firmware topology and include * hooks for test/debug. This allows for the audio core device to be minimal * and focused on hardware-specific control and communication. * * Each auxiliary_device represents a part of its parent functionality. The * generic behavior can be extended and specialized as needed by encapsulating * an auxiliary_device within other domain-specific structures and the use of * .ops callbacks. Devices on the auxiliary bus do not share any structures and * the use of a communication channel with the parent is domain-specific. * * Note that ops are intended as a way to augment instance behavior within a * class of auxiliary devices, it is not the mechanism for exporting common * infrastructure from the parent. Consider EXPORT_SYMBOL_NS() to convey * infrastructure from the parent module to the auxiliary module(s). */ /** * DOC: USAGE * * The auxiliary bus is to be used when a driver and one or more kernel * modules, who share a common header file with the driver, need a mechanism to * connect and provide access to a shared object allocated by the * auxiliary_device's registering driver. The registering driver for the * auxiliary_device(s) and the kernel module(s) registering auxiliary_drivers * can be from the same subsystem, or from multiple subsystems. * * The emphasis here is on a common generic interface that keeps subsystem * customization out of the bus infrastructure. * * One example is a PCI network device that is RDMA-capable and exports a child * device to be driven by an auxiliary_driver in the RDMA subsystem. The PCI * driver allocates and registers an auxiliary_device for each physical * function on the NIC. The RDMA driver registers an auxiliary_driver that * claims each of these auxiliary_devices. This conveys data/ops published by * the parent PCI device/driver to the RDMA auxiliary_driver. * * Another use case is for the PCI device to be split out into multiple sub * functions. For each sub function an auxiliary_device is created. A PCI sub * function driver binds to such devices that creates its own one or more class * devices. A PCI sub function auxiliary device is likely to be contained in a * struct with additional attributes such as user defined sub function number * and optional attributes such as resources and a link to the parent device. * These attributes could be used by systemd/udev; and hence should be * initialized before a driver binds to an auxiliary_device. * * A key requirement for utilizing the auxiliary bus is that there is no * dependency on a physical bus, device, register accesses or regmap support. * These individual devices split from the core cannot live on the platform bus * as 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. */ /** * DOC: EXAMPLE * * Auxiliary devices are created and registered by a subsystem-level core * device that needs to break up its functionality into smaller fragments. One * way to extend the scope of an auxiliary_device is to encapsulate it within a * domain- pecific structure defined by the parent device. This structure * contains the auxiliary_device and any associated shared data/callbacks * needed to establish the connection with the parent. * * An example is: * * .. code-block:: c * * struct foo { * struct auxiliary_device auxdev; * void (*connect)(struct auxiliary_device *auxdev); * void (*disconnect)(struct auxiliary_device *auxdev); * void *data; * }; * * The parent device then registers the auxiliary_device by calling * auxiliary_device_init(), and then auxiliary_device_add(), with the pointer * to the auxdev member of the above structure. The parent provides a name for * the auxiliary_device that, combined with the parent's KBUILD_MODNAME, * creates a match_name that is be used for matching and binding with a driver. * * Whenever an auxiliary_driver is registered, based on the match_name, the * auxiliary_driver's probe() is invoked for the matching devices. The * auxiliary_driver can also be encapsulated inside custom drivers that make * the core device's functionality extensible by adding additional * domain-specific ops as follows: * * .. code-block:: c * * struct my_ops { * void (*send)(struct auxiliary_device *auxdev); * void (*receive)(struct auxiliary_device *auxdev); * }; * * * struct my_driver { * struct auxiliary_driver auxiliary_drv; * const struct my_ops ops; * }; * * An example of this type of usage is: * * .. code-block:: c * * const struct auxiliary_device_id my_auxiliary_id_table[] = { * { .name = "foo_mod.foo_dev" }, * { }, * }; * * const struct my_ops my_custom_ops = { * .send = my_tx, * .receive = my_rx, * }; * * const struct my_driver my_drv = { * .auxiliary_drv = { * .name = "myauxiliarydrv", * .id_table = my_auxiliary_id_table, * .probe = my_probe, * .remove = my_remove, * .shutdown = my_shutdown, * }, * .ops = my_custom_ops, * }; */ static const struct auxiliary_device_id *auxiliary_match_id(const struct auxiliary_device_id *id, const struct auxiliary_device *auxdev) { … } static int auxiliary_match(struct device *dev, const struct device_driver *drv) { … } static int auxiliary_uevent(const struct device *dev, struct kobj_uevent_env *env) { … } static const struct dev_pm_ops auxiliary_dev_pm_ops = …; static int auxiliary_bus_probe(struct device *dev) { … } static void auxiliary_bus_remove(struct device *dev) { … } static void auxiliary_bus_shutdown(struct device *dev) { … } static const struct bus_type auxiliary_bus_type = …; /** * auxiliary_device_init - check auxiliary_device and initialize * @auxdev: auxiliary device struct * * 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 * *not* have been performed, and the caller will be responsible to free any * memory allocated for the auxiliary_device in the error path directly. * * It returns 0 on success. On success, the device_initialize has been * performed. After this point any error unwinding will need to include a call * to auxiliary_device_uninit(). In this post-initialize error scenario, a call * to the device's .release callback will be triggered, and all memory clean-up * is expected to be handled there. */ int auxiliary_device_init(struct auxiliary_device *auxdev) { … } EXPORT_SYMBOL_GPL(…); /** * __auxiliary_device_add - add an auxiliary bus device * @auxdev: auxiliary bus device to add to the bus * @modname: name of the parent device's driver module * * 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 * auxiliary_device_init(), which will perform the device_initialize. This * means that if this returns an error code, then a call to * auxiliary_device_uninit() must be performed so that the .release callback * will be triggered to free the memory associated with the auxiliary_device. * * The expectation is that users will call the "auxiliary_device_add" macro so * that the caller's KBUILD_MODNAME is automatically inserted for the modname * parameter. Only if a user requires a custom name would this version be * called directly. */ int __auxiliary_device_add(struct auxiliary_device *auxdev, const char *modname) { … } EXPORT_SYMBOL_GPL(…); /** * auxiliary_find_device - auxiliary device iterator for locating a particular device. * @start: Device to begin with * @data: Data to pass to match function * @match: Callback function to check device * * This function returns a reference to a device that is 'found' * for later use, as determined by the @match callback. * * The reference returned should be released with put_device(). * * The callback should return 0 if the device doesn't match and non-zero * if it does. If the callback returns non-zero, this function will * return to the caller and not iterate over any more devices. */ struct auxiliary_device *auxiliary_find_device(struct device *start, const void *data, int (*match)(struct device *dev, const void *data)) { … } EXPORT_SYMBOL_GPL(…); /** * __auxiliary_driver_register - register a driver for auxiliary bus devices * @auxdrv: auxiliary_driver structure * @owner: owning module/driver * @modname: KBUILD_MODNAME for parent driver * * The expectation is that users will call the "auxiliary_driver_register" * macro so that the caller's KBUILD_MODNAME is automatically inserted for the * modname parameter. Only if a user requires a custom name would this version * be called directly. */ int __auxiliary_driver_register(struct auxiliary_driver *auxdrv, struct module *owner, const char *modname) { … } EXPORT_SYMBOL_GPL(…); /** * auxiliary_driver_unregister - unregister a driver * @auxdrv: auxiliary_driver structure */ void auxiliary_driver_unregister(struct auxiliary_driver *auxdrv) { … } EXPORT_SYMBOL_GPL(…); void __init auxiliary_bus_init(void) { … }
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