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Date:   Tue, 17 Nov 2020 19:39:14 +0000
From:   Martin Habets <mhabets@solarflare.com>
To:     Dave Ertman <david.m.ertman@intel.com>
CC:     <alsa-devel@alsa-project.org>, <tiwai@suse.de>,
        <broonie@kernel.org>, <linux-rdma@vger.kernel.org>,
        <jgg@nvidia.com>, <dledford@redhat.com>, <netdev@vger.kernel.org>,
        <davem@davemloft.net>, <kuba@kernel.org>,
        <gregkh@linuxfoundation.org>, <ranjani.sridharan@linux.intel.com>,
        <pierre-louis.bossart@linux.intel.com>, <fred.oh@linux.intel.com>,
        <parav@mellanox.com>, <shiraz.saleem@intel.com>,
        <dan.j.williams@intel.com>, <kiran.patil@intel.com>,
        <linux-kernel@vger.kernel.org>, <leonro@nvidia.com>
Subject: Re: [PATCH v4 01/10] Add auxiliary bus support
Message-ID: <20201117193914.GA1555357@mh-desktop>
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        alsa-devel@alsa-project.org, tiwai@suse.de, broonie@kernel.org,
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 <20201113161859.1775473-2-david.m.ertman@intel.com>
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Precedence: bulk

On Fri, Nov 13, 2020 at 08:18:50AM -0800, Dave Ertman wrote:
> Add support for the Auxiliary Bus, auxiliary_device and auxiliary_driver.
> It enables drivers to create an auxiliary_device and bind an
> auxiliary_driver to it.
> 
> The bus supports probe/remove shutdown and suspend/resume callbacks.
> Each auxiliary_device has a unique string based id; driver binds to
> an auxiliary_device based on this id through the bus.

Reviewed-by: Martin Habets <mhabets@solarflare.com>

> Co-developed-by: Kiran Patil <kiran.patil@intel.com>
> Signed-off-by: Kiran Patil <kiran.patil@intel.com>
> Co-developed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
> Signed-off-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
> Co-developed-by: Fred Oh <fred.oh@linux.intel.com>
> Signed-off-by: Fred Oh <fred.oh@linux.intel.com>
> Co-developed-by: Leon Romanovsky <leonro@nvidia.com>
> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
> Reviewed-by: Shiraz Saleem <shiraz.saleem@intel.com>
> Reviewed-by: Parav Pandit <parav@mellanox.com>
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Dave Ertman <david.m.ertman@intel.com>
> ---
>  Documentation/driver-api/auxiliary_bus.rst | 234 ++++++++++++++++++
>  Documentation/driver-api/index.rst         |   1 +
>  drivers/base/Kconfig                       |   3 +
>  drivers/base/Makefile                      |   1 +
>  drivers/base/auxiliary.c                   | 268 +++++++++++++++++++++
>  include/linux/auxiliary_bus.h              |  78 ++++++
>  include/linux/mod_devicetable.h            |   8 +
>  scripts/mod/devicetable-offsets.c          |   3 +
>  scripts/mod/file2alias.c                   |   8 +
>  9 files changed, 604 insertions(+)
>  create mode 100644 Documentation/driver-api/auxiliary_bus.rst
>  create mode 100644 drivers/base/auxiliary.c
>  create mode 100644 include/linux/auxiliary_bus.h
> 
> diff --git a/Documentation/driver-api/auxiliary_bus.rst b/Documentation/driver-api/auxiliary_bus.rst
> new file mode 100644
> index 000000000000..5dd7804631ef
> --- /dev/null
> +++ b/Documentation/driver-api/auxiliary_bus.rst
> @@ -0,0 +1,234 @@
> +.. SPDX-License-Identifier: GPL-2.0-only
> +
> +=============
> +Auxiliary Bus
> +=============
> +
> +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 functinoality 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).
> +
> +
> +When Should the Auxiliary Bus Be Used
> +=====================================
> +
> +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.
> +
> +Auxiliary Device
> +================
> +
> +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 {
> +		struct device dev;
> +                const char *name;
> +		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.
> +
> +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.
> +
> +The auxiliary_device.dev.parent must also be populated.
> +
> +Auxiliary Device Memory Model and Lifespan
> +------------------------------------------
> +
> +The registering driver is the entity that allocates memory for the
> +auxiliary_device and register 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 for the memory used for the driver object.
> +
> +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 auxiliary_device is freed only in its release() callback
> +flow as defined by its registering driver.
> +
> +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 this 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.
> +
> +Auxiliary Drivers
> +=================
> +
> +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.
> +
> +.. code-block:: c
> +
> +	struct auxiliary_driver {
> +		int (*probe)(struct auxiliary_device *,
> +                             const struct auxiliary_device_id *id);
> +		int (*remove)(struct auxiliary_device *);
> +		void (*shutdown)(struct auxiliary_device *);
> +		int (*suspend)(struct auxiliary_device *, pm_message_t);
> +		int (*resume)(struct auxiliary_device *);
> +		struct device_driver driver;
> +		const struct auxiliary_device_id *id_table;
> +	};
> +
> +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.
> +
> +Example Usage
> +=============
> +
> +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,
> +	};
> diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst
> index f357f3eb400c..86759a74b7f1 100644
> --- a/Documentation/driver-api/index.rst
> +++ b/Documentation/driver-api/index.rst
> @@ -72,6 +72,7 @@ available subsections can be seen below.
>     thermal/index
>     fpga/index
>     acpi/index
> +   auxiliary_bus
>     backlight/lp855x-driver.rst
>     connector
>     console
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index 8d7001712062..040be48ce046 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -1,6 +1,9 @@
>  # SPDX-License-Identifier: GPL-2.0
>  menu "Generic Driver Options"
>  
> +config AUXILIARY_BUS
> +	bool
> +
>  config UEVENT_HELPER
>  	bool "Support for uevent helper"
>  	help
> diff --git a/drivers/base/Makefile b/drivers/base/Makefile
> index 41369fc7004f..5e7bf9669a81 100644
> --- a/drivers/base/Makefile
> +++ b/drivers/base/Makefile
> @@ -7,6 +7,7 @@ obj-y			:= component.o core.o bus.o dd.o syscore.o \
>  			   attribute_container.o transport_class.o \
>  			   topology.o container.o property.o cacheinfo.o \
>  			   swnode.o
> +obj-$(CONFIG_AUXILIARY_BUS) += auxiliary.o
>  obj-$(CONFIG_DEVTMPFS)	+= devtmpfs.o
>  obj-y			+= power/
>  obj-$(CONFIG_ISA_BUS_API)	+= isa.o
> diff --git a/drivers/base/auxiliary.c b/drivers/base/auxiliary.c
> new file mode 100644
> index 000000000000..ef2af417438b
> --- /dev/null
> +++ b/drivers/base/auxiliary.c
> @@ -0,0 +1,268 @@
> +// 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) "%s:%s: " fmt, KBUILD_MODNAME, __func__
> +
> +#include <linux/device.h>
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/pm_domain.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/string.h>
> +#include <linux/auxiliary_bus.h>
> +
> +static const struct auxiliary_device_id *auxiliary_match_id(const struct auxiliary_device_id *id,
> +							    const struct auxiliary_device *auxdev)
> +{
> +	for (; id->name[0]; id++) {
> +		const char *p = strrchr(dev_name(&auxdev->dev), '.');
> +		int match_size;
> +
> +		if (!p)
> +			continue;
> +		match_size = p - dev_name(&auxdev->dev);
> +
> +		/* use dev_name(&auxdev->dev) prefix before last '.' char to match to */
> +		if (strlen(id->name) == match_size &&
> +		    !strncmp(dev_name(&auxdev->dev), id->name, match_size))
> +			return id;
> +	}
> +	return NULL;
> +}
> +
> +static int auxiliary_match(struct device *dev, struct device_driver *drv)
> +{
> +	struct auxiliary_device *auxdev = to_auxiliary_dev(dev);
> +	struct auxiliary_driver *auxdrv = to_auxiliary_drv(drv);
> +
> +	return !!auxiliary_match_id(auxdrv->id_table, auxdev);
> +}
> +
> +static int auxiliary_uevent(struct device *dev, struct kobj_uevent_env *env)
> +{
> +	const char *name, *p;
> +
> +	name = dev_name(dev);
> +	p = strrchr(name, '.');
> +
> +	return add_uevent_var(env, "MODALIAS=%s%.*s", AUXILIARY_MODULE_PREFIX, (int)(p - name),
> +			      name);
> +}
> +
> +static const struct dev_pm_ops auxiliary_dev_pm_ops = {
> +	SET_RUNTIME_PM_OPS(pm_generic_runtime_suspend, pm_generic_runtime_resume, NULL)
> +	SET_SYSTEM_SLEEP_PM_OPS(pm_generic_suspend, pm_generic_resume)
> +};
> +
> +static int auxiliary_bus_probe(struct device *dev)
> +{
> +	struct auxiliary_driver *auxdrv = to_auxiliary_drv(dev->driver);
> +	struct auxiliary_device *auxdev = to_auxiliary_dev(dev);
> +	int ret;
> +
> +	ret = dev_pm_domain_attach(dev, true);
> +	if (ret) {
> +		dev_warn(dev, "Failed to attach to PM Domain : %d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = auxdrv->probe(auxdev, auxiliary_match_id(auxdrv->id_table, auxdev));
> +	if (ret)
> +		dev_pm_domain_detach(dev, true);
> +
> +	return ret;
> +}
> +
> +static int auxiliary_bus_remove(struct device *dev)
> +{
> +	struct auxiliary_driver *auxdrv = to_auxiliary_drv(dev->driver);
> +	struct auxiliary_device *auxdev = to_auxiliary_dev(dev);
> +	int ret = 0;
> +
> +	if (auxdrv->remove)
> +		ret = auxdrv->remove(auxdev);
> +	dev_pm_domain_detach(dev, true);
> +
> +	return ret;
> +}
> +
> +static void auxiliary_bus_shutdown(struct device *dev)
> +{
> +	struct auxiliary_driver *auxdrv = to_auxiliary_drv(dev->driver);
> +	struct auxiliary_device *auxdev = to_auxiliary_dev(dev);
> +
> +	if (auxdrv->shutdown)
> +		auxdrv->shutdown(auxdev);
> +}
> +
> +static struct bus_type auxiliary_bus_type = {
> +	.name = "auxiliary",
> +	.probe = auxiliary_bus_probe,
> +	.remove = auxiliary_bus_remove,
> +	.shutdown = auxiliary_bus_shutdown,
> +	.match = auxiliary_match,
> +	.uevent = auxiliary_uevent,
> +	.pm = &auxiliary_dev_pm_ops,
> +};
> +
> +/**
> + * 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 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)
> +{
> +	struct device *dev = &auxdev->dev;
> +
> +	if (!dev->parent) {
> +		pr_err("auxiliary_device has a NULL dev->parent\n");
> +		return -EINVAL;
> +	}
> +
> +	if (!auxdev->name) {
> +		pr_err("auxiliary_device has a NULL name\n");
> +		return -EINVAL;
> +	}
> +
> +	dev->bus = &auxiliary_bus_type;
> +	device_initialize(&auxdev->dev);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(auxiliary_device_init);
> +
> +/**
> + * __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 second step in the two-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)
> +{
> +	struct device *dev = &auxdev->dev;
> +	int ret;
> +
> +	if (!modname) {
> +		pr_err("auxiliary device modname is NULL\n");
> +		return -EINVAL;
> +	}
> +
> +	ret = dev_set_name(dev, "%s.%s.%d", modname, auxdev->name, auxdev->id);
> +	if (ret) {
> +		pr_err("auxiliary device dev_set_name failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = device_add(dev);
> +	if (ret)
> +		dev_err(dev, "adding auxiliary device failed!: %d\n", ret);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(__auxiliary_device_add);
> +
> +/**
> + * 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 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))
> +{
> +	struct device *dev;
> +
> +	dev = bus_find_device(&auxiliary_bus_type, start, data, match);
> +	if (!dev)
> +		return NULL;
> +
> +	return to_auxiliary_dev(dev);
> +}
> +EXPORT_SYMBOL_GPL(auxiliary_find_device);
> +
> +/**
> + * __auxiliary_driver_register - register a driver for auxiliary bus devices
> + * @auxdrv: auxiliary_driver structure
> + * @owner: owning module/driver
> + * @modname: KBUILD_MODNAME for parent driver
> + */
> +int __auxiliary_driver_register(struct auxiliary_driver *auxdrv, struct module *owner,
> +				const char *modname)
> +{
> +	if (WARN_ON(!auxdrv->probe) || WARN_ON(!auxdrv->id_table))
> +		return -EINVAL;
> +
> +	if (auxdrv->name)
> +		auxdrv->driver.name = kasprintf(GFP_KERNEL, "%s.%s", modname, auxdrv->name);
> +	else
> +		auxdrv->driver.name = kasprintf(GFP_KERNEL, "%s", modname);
> +	if (!auxdrv->driver.name)
> +		return -ENOMEM;
> +
> +	auxdrv->driver.owner = owner;
> +	auxdrv->driver.bus = &auxiliary_bus_type;
> +	auxdrv->driver.mod_name = modname;
> +
> +	return driver_register(&auxdrv->driver);
> +}
> +EXPORT_SYMBOL_GPL(__auxiliary_driver_register);
> +
> +/**
> + * auxiliary_driver_unregister - unregister a driver
> + * @auxdrv: auxiliary_driver structure
> + */
> +void auxiliary_driver_unregister(struct auxiliary_driver *auxdrv)
> +{
> +	driver_unregister(&auxdrv->driver);
> +	kfree(auxdrv->driver.name);
> +}
> +EXPORT_SYMBOL_GPL(auxiliary_driver_unregister);
> +
> +static int __init auxiliary_bus_init(void)
> +{
> +	return bus_register(&auxiliary_bus_type);
> +}
> +
> +static void __exit auxiliary_bus_exit(void)
> +{
> +	bus_unregister(&auxiliary_bus_type);
> +}
> +
> +module_init(auxiliary_bus_init);
> +module_exit(auxiliary_bus_exit);
> +
> +MODULE_LICENSE("GPL v2");
> +MODULE_DESCRIPTION("Auxiliary Bus");
> +MODULE_AUTHOR("David Ertman <david.m.ertman@intel.com>");
> +MODULE_AUTHOR("Kiran Patil <kiran.patil@intel.com>");
> diff --git a/include/linux/auxiliary_bus.h b/include/linux/auxiliary_bus.h
> new file mode 100644
> index 000000000000..282fbf7bf9af
> --- /dev/null
> +++ b/include/linux/auxiliary_bus.h
> @@ -0,0 +1,78 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (c) 2019-2020 Intel Corporation
> + *
> + * Please see Documentation/driver-api/auxiliary_bus.rst for more information.
> + */
> +
> +#ifndef _AUXILIARY_BUS_H_
> +#define _AUXILIARY_BUS_H_
> +
> +#include <linux/device.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/slab.h>
> +
> +struct auxiliary_device {
> +	struct device dev;
> +	const char *name;
> +	u32 id;
> +};
> +
> +struct auxiliary_driver {
> +	int (*probe)(struct auxiliary_device *auxdev, const struct auxiliary_device_id *id);
> +	int (*remove)(struct auxiliary_device *auxdev);
> +	void (*shutdown)(struct auxiliary_device *auxdev);
> +	int (*suspend)(struct auxiliary_device *auxdev, pm_message_t state);
> +	int (*resume)(struct auxiliary_device *auxdev);
> +	const char *name;
> +	struct device_driver driver;
> +	const struct auxiliary_device_id *id_table;
> +};
> +
> +static inline struct auxiliary_device *to_auxiliary_dev(struct device *dev)
> +{
> +	return container_of(dev, struct auxiliary_device, dev);
> +}
> +
> +static inline struct auxiliary_driver *to_auxiliary_drv(struct device_driver *drv)
> +{
> +	return container_of(drv, struct auxiliary_driver, driver);
> +}
> +
> +int auxiliary_device_init(struct auxiliary_device *auxdev);
> +int __auxiliary_device_add(struct auxiliary_device *auxdev, const char *modname);
> +#define auxiliary_device_add(auxdev) __auxiliary_device_add(auxdev, KBUILD_MODNAME)
> +
> +static inline void auxiliary_device_uninit(struct auxiliary_device *auxdev)
> +{
> +	put_device(&auxdev->dev);
> +}
> +
> +static inline void auxiliary_device_delete(struct auxiliary_device *auxdev)
> +{
> +	device_del(&auxdev->dev);
> +}
> +
> +int __auxiliary_driver_register(struct auxiliary_driver *auxdrv, struct module *owner,
> +				const char *modname);
> +#define auxiliary_driver_register(auxdrv) \
> +	__auxiliary_driver_register(auxdrv, THIS_MODULE, KBUILD_MODNAME)
> +
> +void auxiliary_driver_unregister(struct auxiliary_driver *auxdrv);
> +
> +/**
> + * module_auxiliary_driver() - Helper macro for registering an auxiliary driver
> + * @__auxiliary_driver: auxiliary driver struct
> + *
> + * Helper macro for auxiliary drivers which do not do anything special in
> + * module init/exit. This eliminates a lot of boilerplate. Each module may only
> + * use this macro once, and calling it replaces module_init() and module_exit()
> + */
> +#define module_auxiliary_driver(__auxiliary_driver) \
> +	module_driver(__auxiliary_driver, auxiliary_driver_register, auxiliary_driver_unregister)
> +
> +struct auxiliary_device *
> +auxiliary_find_device(struct device *start, const void *data,
> +		      int (*match)(struct device *dev, const void *data));
> +
> +#endif /* _AUXILIARY_BUS_H_ */
> diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
> index 5b08a473cdba..c425290b21e2 100644
> --- a/include/linux/mod_devicetable.h
> +++ b/include/linux/mod_devicetable.h
> @@ -838,4 +838,12 @@ struct mhi_device_id {
>  	kernel_ulong_t driver_data;
>  };
>  
> +#define AUXILIARY_NAME_SIZE 32
> +#define AUXILIARY_MODULE_PREFIX "auxiliary:"
> +
> +struct auxiliary_device_id {
> +	char name[AUXILIARY_NAME_SIZE];
> +	kernel_ulong_t driver_data;
> +};
> +
>  #endif /* LINUX_MOD_DEVICETABLE_H */
> diff --git a/scripts/mod/devicetable-offsets.c b/scripts/mod/devicetable-offsets.c
> index 27007c18e754..e377f52dbfa3 100644
> --- a/scripts/mod/devicetable-offsets.c
> +++ b/scripts/mod/devicetable-offsets.c
> @@ -243,5 +243,8 @@ int main(void)
>  	DEVID(mhi_device_id);
>  	DEVID_FIELD(mhi_device_id, chan);
>  
> +	DEVID(auxiliary_device_id);
> +	DEVID_FIELD(auxiliary_device_id, name);
> +
>  	return 0;
>  }
> diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
> index 2417dd1dee33..fb4827027536 100644
> --- a/scripts/mod/file2alias.c
> +++ b/scripts/mod/file2alias.c
> @@ -1364,6 +1364,13 @@ static int do_mhi_entry(const char *filename, void *symval, char *alias)
>  {
>  	DEF_FIELD_ADDR(symval, mhi_device_id, chan);
>  	sprintf(alias, MHI_DEVICE_MODALIAS_FMT, *chan);
> +	return 1;
> +}
> +
> +static int do_auxiliary_entry(const char *filename, void *symval, char *alias)
> +{
> +	DEF_FIELD_ADDR(symval, auxiliary_device_id, name);
> +	sprintf(alias, AUXILIARY_MODULE_PREFIX "%s", *name);
>  
>  	return 1;
>  }
> @@ -1442,6 +1449,7 @@ static const struct devtable devtable[] = {
>  	{"tee", SIZE_tee_client_device_id, do_tee_entry},
>  	{"wmi", SIZE_wmi_device_id, do_wmi_entry},
>  	{"mhi", SIZE_mhi_device_id, do_mhi_entry},
> +	{"auxiliary", SIZE_auxiliary_device_id, do_auxiliary_entry},
>  };
>  
>  /* Create MODULE_ALIAS() statements.
> -- 
> 2.26.2

-- 
Martin Habets <mhabets@solarflare.com>