Device Driver Model

Introduction

The Zephyr kernel supports a variety of device drivers. Whether a driver is available depends on the board and the driver.

The Zephyr device model provides a consistent device model for configuring the drivers that are part of a system. The device model is responsible for initializing all the drivers configured into the system.

Each type of driver (e.g. UART, SPI, I2C) is supported by a generic type API.

In this model the driver fills in the pointer to the structure containing the function pointers to its API functions during driver initialization. These structures are placed into the RAM section in initialization level order.

Standard Drivers

Device drivers which are present on all supported board configurations are listed below.

Interrupt controller: This device driver is used by the kernel’s interrupt management subsystem.
Timer: This device driver is used by the kernel’s system clock and hardware clock subsystem.
Serial communication: This device driver is used by the kernel’s system console subsystem.
Entropy: This device driver provides a source of entropy numbers for the random number generator subsystem.

Important

Use the random API functions for random values. Entropy functions should not be directly used as a random number generator source as some hardware implementations are designed to be an entropy seed source for random number generators and will not provide cryptographically secure random number streams.

Synchronous Calls

Zephyr provides a set of device drivers for multiple boards. Each driver should support an interrupt-based implementation, rather than polling, unless the specific hardware does not provide any interrupt.

High-level calls accessed through device-specific APIs, such as i2c.h or spi.h, are usually intended as synchronous. Thus, these calls should be blocking.

Driver APIs

The following APIs for device drivers are provided by device.h. The APIs are intended for use in device drivers only and should not be used in applications.

DEVICE_DEFINE(): Create device object and related data structures including setting it up for boot-time initialization.
DEVICE_NAME_GET(): Converts a device identifier to the global identifier for a device object.
DEVICE_GET(): Obtain a pointer to a device object by name.
DEVICE_DECLARE(): Declare a device object. Use this when you need a forward reference to a device that has not yet been defined.

Driver Data Structures

The device initialization macros populate some data structures at build time which are split into read-only and runtime-mutable parts. At a high level we have:

struct device {
      const char *name;
      const void *config;
      const void *api;
      void * const data;
};

The config member is for read-only configuration data set at build time. For example, base memory mapped IO addresses, IRQ line numbers, or other fixed physical characteristics of the device. This is the config pointer passed to DEVICE_DEFINE() and related macros.

The data struct is kept in RAM, and is used by the driver for per-instance runtime housekeeping. For example, it may contain reference counts, semaphores, scratch buffers, etc.

The api struct maps generic subsystem APIs to the device-specific implementations in the driver. It is typically read-only and populated at build time. The next section describes this in more detail.

Subsystems and API Structures

Most drivers will be implementing a device-independent subsystem API. Applications can simply program to that generic API, and application code is not specific to any particular driver implementation.

A subsystem API definition typically looks like this:

typedef int (*subsystem_do_this_t)(const struct device *dev, int foo, int bar);
typedef void (*subsystem_do_that_t)(const struct device *dev, void *baz);

struct subsystem_api {
      subsystem_do_this_t do_this;
      subsystem_do_that_t do_that;
};

static inline int subsystem_do_this(const struct device *dev, int foo, int bar)
{
      struct subsystem_api *api;

      api = (struct subsystem_api *)dev->api;
      return api->do_this(dev, foo, bar);
}

static inline void subsystem_do_that(const struct device *dev, void *baz)
{
      struct subsystem_api *api;

      api = (struct subsystem_api *)dev->api;
      api->do_that(dev, baz);
}

A driver implementing a particular subsystem will define the real implementation of these APIs, and populate an instance of subsystem_api structure:

static int my_driver_do_this(const struct device *dev, int foo, int bar)
{
      ...
}

static void my_driver_do_that(const struct device *dev, void *baz)
{
      ...
}

static struct subsystem_api my_driver_api_funcs = {
      .do_this = my_driver_do_this,
      .do_that = my_driver_do_that
};

The driver would then pass my_driver_api_funcs as the api argument to DEVICE_DEFINE().

Note

Since pointers to the API functions are referenced in the api struct, they will always be included in the binary even if unused; gc-sections linker option will always see at least one reference to them. Providing for link-time size optimizations with driver APIs in most cases requires that the optional feature be controlled by a Kconfig option.

Device-Specific API Extensions

Some devices can be cast as an instance of a driver subsystem such as GPIO, but provide additional functionality that cannot be exposed through the standard API. These devices combine subsystem operations with device-specific APIs, described in a device-specific header.

A device-specific API definition typically looks like this:

#include <drivers/subsystem.h>

/* When extensions need not be invoked from user mode threads */
int specific_do_that(const struct device *dev, int foo);

/* When extensions must be invokable from user mode threads */
__syscall int specific_from_user(const struct device *dev, int bar);

/* Only needed when extensions include syscalls */
#include <syscalls/specific.h>

A driver implementing extensions to the subsystem will define the real implementation of both the subsystem API and the specific APIs:

static int generic_do_this(const struct device *dev, void *arg)
{
   ...
}

static struct generic_api api {
   ...
   .do_this = generic_do_this,
   ...
};

/* supervisor-only API is globally visible */
int specific_do_that(const struct device *dev, int foo)
{
   ...
}

/* syscall API passes through a translation */
int z_impl_specific_from_user(const struct device *dev, int bar)
{
   ...
}

#ifdef CONFIG_USERSPACE

#include <syscall_handler.h>

int z_vrfy_specific_from_user(const struct device *dev, int bar)
{
    Z_OOPS(Z_SYSCALL_SPECIFIC_DRIVER(dev, K_OBJ_DRIVER_GENERIC, &api));
    return z_impl_specific_do_that(dev, bar)
}

#include <syscalls/specific_from_user_mrsh.c>

#endif /* CONFIG_USERSPACE */

Applications use the device through both the subsystem and specific APIs.

Note

Public API for device-specific extensions should be prefixed with the compatible for the device to which it applies. For example, if adding special functions to support the Maxim DS3231 the identifier fragment specific in the examples above would be maxim_ds3231.

Single Driver, Multiple Instances

Some drivers may be instantiated multiple times in a given system. For example there can be multiple GPIO banks, or multiple UARTS. Each instance of the driver will have a different config struct and data struct.

Configuring interrupts for multiple drivers instances is a special case. If each instance needs to configure a different interrupt line, this can be accomplished through the use of per-instance configuration functions, since the parameters to IRQ_CONNECT() need to be resolvable at build time.

For example, let’s say we need to configure two instances of my_driver, each with a different interrupt line. In drivers/subsystem/subsystem_my_driver.h:

typedef void (*my_driver_config_irq_t)(const struct device *dev);

struct my_driver_config {
      DEVICE_MMIO_ROM;
      my_driver_config_irq_t config_func;
};

In the implementation of the common init function:

void my_driver_isr(const struct device *dev)
{
      /* Handle interrupt */
      ...
}

int my_driver_init(const struct device *dev)
{
      const struct my_driver_config *config = dev->config;

      DEVICE_MMIO_MAP(dev, K_MEM_CACHE_NONE);

      /* Do other initialization stuff */
      ...

      config->config_func(dev);

      return 0;
}

Then when the particular instance is declared:

#if CONFIG_MY_DRIVER_0

DEVICE_DECLARE(my_driver_0);

static void my_driver_config_irq_0(void)
{
      IRQ_CONNECT(MY_DRIVER_0_IRQ, MY_DRIVER_0_PRI, my_driver_isr,
                  DEVICE_GET(my_driver_0), MY_DRIVER_0_FLAGS);
}

const static struct my_driver_config my_driver_config_0 = {
      DEVICE_MMIO_ROM_INIT(DT_DRV_INST(0)),
      .config_func = my_driver_config_irq_0
}

static struct my_data_0;

DEVICE_DEFINE(my_driver_0, MY_DRIVER_0_NAME, my_driver_init,
              NULL, &my_data_0, &my_driver_config_0,
              POST_KERNEL, MY_DRIVER_0_PRIORITY, &my_api_funcs);

#endif /* CONFIG_MY_DRIVER_0 */

Note the use of DEVICE_DECLARE() to avoid a circular dependency on providing the IRQ handler argument and the definition of the device itself.

Initialization Levels

Drivers may depend on other drivers being initialized first, or require the use of kernel services. DEVICE_DEFINE() and related APIs allow the user to specify at what time during the boot sequence the init function will be executed. Any driver will specify one of four initialization levels:

PRE_KERNEL_1: Used for devices that have no dependencies, such as those that rely solely on hardware present in the processor/SOC. These devices cannot use any kernel services during configuration, since the kernel services are not yet available. The interrupt subsystem will be configured however so it’s OK to set up interrupts. Init functions at this level run on the interrupt stack.
PRE_KERNEL_2: Used for devices that rely on the initialization of devices initialized as part of the PRE_KERNEL_1 level. These devices cannot use any kernel services during configuration, since the kernel services are not yet available. Init functions at this level run on the interrupt stack.
POST_KERNEL: Used for devices that require kernel services during configuration. Init functions at this level run in context of the kernel main task.
APPLICATION: Used for application components (i.e. non-kernel components) that need automatic configuration. These devices can use all services provided by the kernel during configuration. Init functions at this level run on the kernel main task.

Within each initialization level you may specify a priority level, relative to other devices in the same initialization level. The priority level is specified as an integer value in the range 0 to 99; lower values indicate earlier initialization. The priority level must be a decimal integer literal without leading zeroes or sign (e.g. 32), or an equivalent symbolic name (e.g. \#define MY_INIT_PRIO 32); symbolic expressions are not permitted (e.g. CONFIG_KERNEL_INIT_PRIORITY_DEFAULT + 5).

Drivers and other system utilities can determine whether startup is still in pre-kernel states by using the k_is_pre_kernel() function.

System Drivers

In some cases you may just need to run a function at boot. For such cases, the SYS_INIT can be used. This macro does not take any config or runtime data structures and there isn’t a way to later get a device pointer by name. The same device policies for initialization level and priority apply.

Error handling

In general, it’s best to use __ASSERT() macros instead of propagating return values unless the failure is expected to occur during the normal course of operation (such as a storage device full). Bad parameters, programming errors, consistency checks, pathological/unrecoverable failures, etc., should be handled by assertions.

When it is appropriate to return error conditions for the caller to check, 0 should be returned on success and a POSIX errno.h code returned on failure. See https://github.com/zephyrproject-rtos/zephyr/wiki/Naming-Conventions#return-codes for details about this.

Memory Mapping

On some systems, the linear address of peripheral memory-mapped I/O (MMIO) regions cannot be known at build time:

The I/O ranges must be probed at runtime from the bus, such as with PCI express
A memory management unit (MMU) is active, and the physical address of the MMIO range must be mapped into the page tables at some virtual memory location determined by the kernel.

These systems must maintain storage for the MMIO range within RAM and establish the mapping within the driver’s init function. Other systems do not care about this and can use MMIO physical addresses directly from DTS and do not need any RAM-based storage for it.

For drivers that may need to deal with this situation, a set of APIs under the DEVICE_MMIO scope are defined, along with a mapping function device_map().

Device Model Drivers with one MMIO region

The simplest case is for drivers which need to maintain one MMIO region. These drivers will need to use the DEVICE_MMIO_ROM and DEVICE_MMIO_RAM macros in the definitions for their config_info and driver_data structures, with initialization of the config_info from DTS using DEVICE_MMIO_ROM_INIT. A call to DEVICE_MMIO_MAP() is made within the init function:

struct my_driver_config {
   DEVICE_MMIO_ROM; /* Must be first */
   ...
}

struct my_driver_dev_data {
   DEVICE_MMIO_RAM; /* Must be first */
   ...
}

const static struct my_driver_config my_driver_config_0 = {
   DEVICE_MMIO_ROM_INIT(DT_DRV_INST(...)),
   ...
}

int my_driver_init(const struct device *dev)
{
   ...
   DEVICE_MMIO_MAP(dev, K_MEM_CACHE_NONE);
   ...
}

int my_driver_some_function(const struct device *dev)
{
   ...
   /* Write some data to the MMIO region */
   sys_write32(0xDEADBEEF, DEVICE_MMIO_GET(dev));
   ...
}

The particular expansion of these macros depends on configuration. On a device with no MMU or PCI-e, DEVICE_MMIO_MAP and DEVICE_MMIO_RAM expand to nothing.

Device Model Drivers with multiple MMIO regions

Some drivers may have multiple MMIO regions. In addition, some drivers may already be implementing a form of inheritance which requires some other data to be placed first in the config_info and driver_data structures.

This can be managed with the DEVICE_MMIO_NAMED variant macros. These require that DEV_CFG() and DEV_DATA() macros be defined to obtain a properly typed pointer to the driver’s config_info or dev_data structs. For example:

struct my_driver_config {
   ...
     DEVICE_MMIO_NAMED_ROM(corge);
     DEVICE_MMIO_NAMED_ROM(grault);
   ...
}

struct my_driver_dev_data {
        ...
     DEVICE_MMIO_NAMED_RAM(corge);
     DEVICE_MMIO_NAMED_RAM(grault);
     ...
}

#define DEV_CFG(_dev) \
   ((const struct my_driver_config *)((_dev)->config))

#define DEV_DATA(_dev) \
   ((struct my_driver_dev_data *)((_dev)->data))

const static struct my_driver_config my_driver_config_0 = {
   ...
   DEVICE_MMIO_NAMED_ROM_INIT(corge, DT_DRV_INST(...)),
   DEVICE_MMIO_NAMED_ROM_INIT(grault, DT_DRV_INST(...)),
   ...
}

int my_driver_init(const struct device *dev)
{
   ...
   DEVICE_MMIO_NAMED_MAP(dev, corge, K_MEM_CACHE_NONE);
   DEVICE_MMIO_NAMED_MAP(dev, grault, K_MEM_CACHE_NONE);
   ...
}

int my_driver_some_function(const struct device *dev)
{
   ...
   /* Write some data to the MMIO regions */
   sys_write32(0xDEADBEEF, DEVICE_MMIO_GET(dev, grault));
   sys_write32(0xF0CCAC1A, DEVICE_MMIO_GET(dev, corge));
   ...
}

Drivers that do not use Zephyr Device Model

Some drivers or driver-like code may not user Zephyr’s device model, and alternative storage must be arranged for the MMIO data. An example of this are timer drivers, or interrupt controller code.

This can be managed with the DEVICE_MMIO_TOPLEVEL set of macros, for example:

DEVICE_MMIO_TOPLEVEL_STATIC(my_regs, DT_DRV_INST(..));

void some_init_code(...)
{
   ...
   DEVICE_MMIO_TOPLEVEL_MAP(my_regs, K_MEM_CACHE_NONE);
   ...
}

void some_function(...)
   ...
   sys_write32(DEVICE_MMIO_TOPLEVEL_GET(my_regs), 0xDEADBEEF);
   ...
}

Drivers that do not use DTS

Some drivers may not obtain the MMIO physical address from DTS, such as is the case with PCI-E. In this case the device_map() function may be used directly:

void some_init_code(...)
{
   ...
   struct pcie_mbar mbar;
   bool bar_found = pcie_get_mbar(bdf, index, &mbar);

   device_map(DEVICE_MMIO_RAM_PTR(dev), mbar.phys_addr, mbar.size, K_MEM_CACHE_NONE);
   ...
}

For these cases, DEVICE_MMIO_ROM directives may be omitted.

API Reference

group device_model

Device Model APIs.

Defines

DEVICE_HANDLE_SEP

Flag value used in lists of device handles to separate distinct groups.

This is the minimum value for the device_handle_t type.

DEVICE_HANDLE_ENDS

Flag value used in lists of device handles to indicate the end of the list.

This is the maximum value for the device_handle_t type.

DEVICE_HANDLE_NULL: Flag value used to identify an unknown device.

DEVICE_NAME_GET(name)

Expands to the name of a global device object.

Return the full name of a device object symbol created by DEVICE_DEFINE(), using the dev_name provided to DEVICE_DEFINE(). This is the name of the global variable storing the device structure, not a pointer to the string in the device’s name field.

It is meant to be used for declaring extern symbols pointing to device objects before using the DEVICE_GET macro to get the device object.

This macro is normally only useful within device driver source code. In other situations, you are probably looking for device_get_binding().

Parameters

name – The same dev_name token given to DEVICE_DEFINE()

Returns

The full name of the device object defined by DEVICE_DEFINE()

SYS_DEVICE_DEFINE(drv_name, init_fn, level, prio)

Run an initialization function at boot at specified priority.

Deprecated:: Use SYS_INIT() instead.

Parameters

drv_name – A string name for the pseudo-device (unused).
init_fn – Pointer to the function which should run at boot time.
level – Initialization level to run the function in.
prio – Function’s priority within its initialization level.

DEVICE_DEFINE(dev_name, drv_name, init_fn, pm_device, data_ptr, cfg_ptr, level, prio, api_ptr)

Create a device object and set it up for boot time initialization.

This macro defines a struct device that is automatically configured by the kernel during system initialization. This macro should only be used when the device is not being allocated from a devicetree node. If you are allocating a device from a devicetree node, use DEVICE_DT_DEFINE() or DEVICE_DT_INST_DEFINE() instead.

Parameters

dev_name – A unique token which is used in the name of the global device structure as a C identifier.
drv_name – A string name for the device, which will be stored in the device structure’s name field. This name can be used to look up the device with device_get_binding(). This must be less than Z_DEVICE_MAX_NAME_LEN characters (including terminating NUL) in order to be looked up from user mode.
init_fn – Pointer to the device’s initialization function, which will be run by the kernel during system initialization.
pm_device – Pointer to the device’s power management resources, a struct pm_device, which will be stored in the device structure’s pm field. Use NULL if the device does not use PM.
data_ptr – Pointer to the device’s private mutable data, which will be stored in the device structure’s data field.
cfg_ptr – Pointer to the device’s private constant data, which will be stored in the device structure’s config field.
level – The device’s initialization level. See SYS_INIT() for details.
prio – The device’s priority within its initialization level. See SYS_INIT() for details.
api_ptr – Pointer to the device’s API structure. Can be NULL.

DEVICE_DT_NAME(node_id)

Return a string name for a devicetree node.

This macro returns a string literal usable as a device’s name field from a devicetree node identifier.

Parameters

node_id – The devicetree node identifier.

Returns

The value of the node’s “label” property, if it has one. Otherwise, the node’s full name in “node-name@@unit-address” form.

DEVICE_DT_DEFINE(node_id, init_fn, pm_device, data_ptr, cfg_ptr, level, prio, api_ptr, ...)

Create a device object from a devicetree node identifier and set it up for boot time initialization.

This macro defines a struct device that is automatically configured by the kernel during system initialization. The global device object’s name as a C identifier is derived from the node’s dependency ordinal. The device structure’s name field is set to DEVICE_DT_NAME(node_id).

The device is declared with extern visibility, so a pointer to a global device object can be obtained with DEVICE_DT_GET(node_id) from any source file that includes device.h. Before using the pointer, the referenced object should be checked using device_is_ready().

Parameters

node_id – The devicetree node identifier.
init_fn – Pointer to the device’s initialization function, which will be run by the kernel during system initialization.
pm_device – Pointer to the device’s power management resources, a struct pm_device, which will be stored in the device structure’s pm field. Use NULL if the device does not use PM.
data_ptr – Pointer to the device’s private mutable data, which will be stored in the device structure’s data field.
cfg_ptr – Pointer to the device’s private constant data, which will be stored in the device structure’s config field.
level – The device’s initialization level. See SYS_INIT() for details.
prio – The device’s priority within its initialization level. See SYS_INIT() for details.
api_ptr – Pointer to the device’s API structure. Can be NULL.

DEVICE_DT_INST_DEFINE(inst, ...)

Like DEVICE_DT_DEFINE(), but uses an instance of a DT_DRV_COMPAT compatible instead of a node identifier.

Parameters

inst – instance number. The node_id argument to DEVICE_DT_DEFINE is set to DT_DRV_INST(inst).
... – other parameters as expected by DEVICE_DT_DEFINE.

DEVICE_DT_NAME_GET(node_id)

The name of the global device object for node_id.

Returns the name of the global device structure as a C identifier. The device must be allocated using DEVICE_DT_DEFINE() or DEVICE_DT_INST_DEFINE() for this to work.

This macro is normally only useful within device driver source code. In other situations, you are probably looking for DEVICE_DT_GET().

Parameters

node_id – Devicetree node identifier

Returns

The name of the device object as a C identifier

DEVICE_DT_GET(node_id)

Get a const struct device* from a devicetree node identifier.

Returns a pointer to a device object created from a devicetree node, if any device was allocated by a driver.

If no such device was allocated, this will fail at linker time. If you get an error that looks like undefined reference to __device_dts_ord_<N>, that is what happened. Check to make sure your device driver is being compiled, usually by enabling the Kconfig options it requires.

Parameters

node_id – A devicetree node identifier

Returns

A pointer to the device object created for that node

DEVICE_DT_INST_GET(inst)

Get a const struct device* for an instance of a DT_DRV_COMPAT compatible.

This is equivalent to DEVICE_DT_GET(DT_DRV_INST(inst)).

Parameters

inst – DT_DRV_COMPAT instance number

Returns

A pointer to the device object created for that instance

DEVICE_DT_GET_ANY(compat)

Get a const struct device* from a devicetree compatible.

If an enabled devicetree node has the given compatible and a device object was created from it, this returns a pointer to that device.

If there no such devices, this returns NULL.

If there are multiple, this returns an arbitrary one.

If this returns non-NULL, the device must be checked for readiness before use, e.g. with device_is_ready().

Parameters

compat – lowercase-and-underscores devicetree compatible

Returns

a pointer to a device, or NULL

DEVICE_DT_GET_ONE(compat)

Get a const struct device* from a devicetree compatible.

If an enabled devicetree node has the given compatible and a device object was created from it, this returns a pointer to that device.

If there no such devices, this will fail at compile time.

If there are multiple, this returns an arbitrary one.

If this returns non-NULL, the device must be checked for readiness before use, e.g. with device_is_ready().

Parameters

compat – lowercase-and-underscores devicetree compatible

Returns

a pointer to a device

DEVICE_DT_GET_OR_NULL(node_id)

Utility macro to obtain an optional reference to a device.

If the node identifier refers to a node with status “okay”, this returns DEVICE_DT_GET(node_id). Otherwise, it returns NULL.

Parameters

node_id – devicetree node identifier

Returns

a const struct device* for the node identifier, which may be NULL.

DEVICE_GET(name)

Obtain a pointer to a device object by name.

Return the address of a device object created by DEVICE_DEFINE(), using the dev_name provided to DEVICE_DEFINE().

Parameters

name – The same as dev_name provided to DEVICE_DEFINE()

Returns

A pointer to the device object created by DEVICE_DEFINE()

DEVICE_DECLARE(name)

Declare a static device object.

This macro can be used at the top-level to declare a device, such that DEVICE_GET() may be used before the full declaration in DEVICE_DEFINE().

This is often useful when configuring interrupts statically in a device’s init or per-instance config function, as the init function itself is required by DEVICE_DEFINE() and use of DEVICE_GET() inside it creates a circular dependency.

Parameters

name – Device name

SYS_INIT(_init_fn, _level, _prio)

Run an initialization function at boot at specified priority.

This macro lets you run a function at system boot.

Parameters

_init_fn – Pointer to the boot function to run
_level – The initialization level at which configuration occurs. Must be one of the following symbols, which are listed in the order they are performed by the kernel:
- PRE_KERNEL_1: Used for initialization objects that have no dependencies, such as those that rely solely on hardware present in the processor/SOC. These objects cannot use any kernel services during configuration, since they are not yet available.
- PRE_KERNEL_2: Used for initialization objects that rely on objects initialized as part of the PRE_KERNEL_1 level. These objects cannot use any kernel services during configuration, since they are not yet available.
- POST_KERNEL: Used for initialization objects that require kernel services during configuration.
- POST_KERNEL_SMP: Used for initialization objects that require kernel services during configuration after SMP initialization.
- APPLICATION: Used for application components (i.e. non-kernel components) that need automatic configuration. These objects can use all services provided by the kernel during configuration.
_prio – The initialization priority of the object, relative to other objects of the same initialization level. Specified as an integer value in the range 0 to 99; lower values indicate earlier initialization. Must be a decimal integer literal without leading zeroes or sign (e.g. 32), or an equivalent symbolic name (e.g. #define MY_INIT_PRIO 32); symbolic expressions are not permitted (e.g. CONFIG_KERNEL_INIT_PRIORITY_DEFAULT + 5).

Typedefs

typedef int16_t device_handle_t

Type used to represent a “handle” for a device.

Every struct device has an associated handle. You can get a pointer to a device structure from its handle and vice versa, but the handle uses less space than a pointer. The device.h API mainly uses handles to store lists of multiple devices in a compact way.

The extreme values and zero have special significance. Negative values identify functionality that does not correspond to a Zephyr device, such as the system clock or a SYS_INIT() function.

See also

device_handle_get()

See also

device_from_handle()

typedef int (*device_visitor_callback_t)(const struct device *dev, void *context)

Prototype for functions used when iterating over a set of devices.

Such a function may be used in API that identifies a set of devices and provides a visitor API supporting caller-specific interaction with each device in the set.

The visit is said to succeed if the visitor returns a non-negative value.

See also

device_required_foreach()

See also

device_supported_foreach()

Param dev: a device in the set being iterated
Param context: state used to support the visitor function
Return: A non-negative number to allow walking to continue, and a negative error code to case the iteration to stop.

Functions

static inline device_handle_t device_handle_get(const struct device *dev)

Get the handle for a given device.

Parameters

dev – the device for which a handle is desired.

Returns

the handle for the device, or DEVICE_HANDLE_NULL if the device does not have an associated handle.

static inline const struct device *device_from_handle(device_handle_t dev_handle)

Get the device corresponding to a handle.

Parameters

dev_handle – the device handle

Returns

the device that has that handle, or a null pointer if dev_handle does not identify a device.

static inline const device_handle_t *device_required_handles_get(const struct device *dev, size_t *count)

Get the device handles for devicetree dependencies of this device.

This function returns a pointer to an array of device handles. The length of the array is stored in the count parameter.

The array contains a handle for each device that dev requires directly, as determined from the devicetree. This does not include transitive dependencies; you must recursively determine those.

Parameters

dev – the device for which dependencies are desired.
count – pointer to where this function should store the length of the returned array. No value is stored if the call returns a null pointer. The value may be set to zero if the device has no devicetree dependencies.

Returns

a pointer to a sequence of *count device handles, or a null pointer if dev does not have any dependency data.

static inline const device_handle_t *device_supported_handles_get(const struct device *dev, size_t *count)

Get the set of handles that this device supports.

This function returns a pointer to an array of device handles. The length of the array is stored in the count parameter.

The array contains a handle for each device that dev “supports” — that is, devices that require dev directly — as determined from the devicetree. This does not include transitive dependencies; you must recursively determine those.

Parameters

dev – the device for which supports are desired.
count – pointer to where this function should store the length of the returned array. No value is stored if the call returns a null pointer. The value may be set to zero if nothing in the devicetree depends on dev.

Returns

a pointer to a sequence of *count device handles, or a null pointer if dev does not have any dependency data.

int device_required_foreach(const struct device *dev, device_visitor_callback_t visitor_cb, void *context)

Visit every device that dev directly requires.

Zephyr maintains information about which devices are directly required by another device; for example an I2C-based sensor driver will require an I2C controller for communication. Required devices can derive from statically-defined devicetree relationships or dependencies registered at runtime.

This API supports operating on the set of required devices. Example uses include making sure required devices are ready before the requiring device is used, and releasing them when the requiring device is no longer needed.

There is no guarantee on the order in which required devices are visited.

If the visitor function returns a negative value iteration is halted, and the returned value from the visitor is returned from this function.

Note

This API is not available to unprivileged threads.

Parameters

dev – a device of interest. The devices that this device depends on will be used as the set of devices to visit. This parameter must not be null.
visitor_cb – the function that should be invoked on each device in the dependency set. This parameter must not be null.
context – state that is passed through to the visitor function. This parameter may be null if visitor tolerates a null context.

Returns

The number of devices that were visited if all visits succeed, or the negative value returned from the first visit that did not succeed.

int device_supported_foreach(const struct device *dev, device_visitor_callback_t visitor_cb, void *context)

Visit every device that dev directly supports.

Zephyr maintains information about which devices are directly supported by another device; for example an I2C controller will support an I2C-based sensor driver. Supported devices can derive from statically-defined devicetree relationships.

This API supports operating on the set of supported devices. Example uses include iterating over the devices connected to a regulator when it is powered on.

There is no guarantee on the order in which required devices are visited.

If the visitor function returns a negative value iteration is halted, and the returned value from the visitor is returned from this function.

Note

This API is not available to unprivileged threads.

Parameters

dev – a device of interest. The devices that this device supports will be used as the set of devices to visit. This parameter must not be null.
visitor_cb – the function that should be invoked on each device in the support set. This parameter must not be null.
context – state that is passed through to the visitor function. This parameter may be null if visitor tolerates a null context.

Returns

The number of devices that were visited if all visits succeed, or the negative value returned from the first visit that did not succeed.

const struct device *device_get_binding(const char *name)

Get a const struct device* from its name field.

This function iterates through the devices on the system. If a device with the given name field is found, and that device initialized successfully at boot time, this function returns a pointer to the device.

If no device has the given name, this function returns NULL.

This function also returns NULL when a device is found, but it failed to initialize successfully at boot time. (To troubleshoot this case, set a breakpoint on your device driver’s initialization function.)

Parameters

name – device name to search for. A null pointer, or a pointer to an empty string, will cause NULL to be returned.

Returns

pointer to device structure with the given name; NULL if the device is not found or if the device with that name’s initialization function failed.

int device_usable_check(const struct device *dev)

Determine whether a device is ready for use.

This checks whether a device can be used, returning 0 if it can, and distinct error values that identify the reason if it cannot.

Return values

0 – if the device is usable.
-ENODEV – if the device has not been initialized, the device pointer is NULL or the initialization failed.
other – negative error codes to indicate additional conditions that make the device unusable.

static inline bool device_is_ready(const struct device *dev)

Verify that a device is ready for use.

Indicates whether the provided device pointer is for a device known to be in a state where it can be used with its standard API.

This can be used with device pointers captured from DEVICE_DT_GET(), which does not include the readiness checks of device_get_binding(). At minimum this means that the device has been successfully initialized, but it may take on further conditions (e.g. is not powered down).

Parameters

dev – pointer to the device in question.

Return values

true – if the device is ready for use.
false – if the device is not ready for use or if a NULL device pointer is passed as argument.

struct device_state

#include <device.h>

Runtime device dynamic structure (in RAM) per driver instance.

Fields in this are expected to be default-initialized to zero. The kernel driver infrastructure and driver access functions are responsible for ensuring that any non-zero initialization is done before they are accessed.

Public Members

unsigned int init_res

Non-negative result of initializing the device.

The absolute value returned when the device initialization function was invoked, or UINT8_MAX if the value exceeds an 8-bit integer. If initialized is also set, a zero value indicates initialization succeeded.

bool initialized: Indicates the device initialization function has been invoked.

struct device

#include <device.h>

Runtime device structure (in ROM) per driver instance.

Public Members

const char *name: Name of the device instance

const void *config: Address of device instance config information

const void *api: Address of the API structure exposed by the device instance

struct device_state *const state: Address of the common device state

void *const data: Address of the device instance private data

const device_handle_t *const handles

optional pointer to handles associated with the device.

This encodes a sequence of sets of device handles that have some relationship to this node. The individual sets are extracted with dedicated API, such as device_required_handles_get().