struct device
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## Name

struct device — The basic device structure

## Synopsis

    struct device {
      struct device * parent;
      struct device_private * p;
      struct kobject kobj;
      const char * init_name;
      const struct device_type * type;
      struct mutex mutex;
      struct bus_type * bus;
      struct device_driver * driver;
      void * platform_data;
      struct dev_pm_info power;
      struct dev_pm_domain * pm_domain;
    #ifdef CONFIG_PINCTRL
      struct dev_pin_info * pins;
    #endif
    #ifdef CONFIG_NUMA
      int numa_node;
    #endif
      u64 * dma_mask;
      u64 coherent_dma_mask;
      struct device_dma_parameters * dma_parms;
      struct list_head dma_pools;
      struct dma_coherent_mem * dma_mem;
    #ifdef CONFIG_DMA_CMA
      struct cma * cma_area;
    #endif
      struct dev_archdata archdata;
      struct device_node * of_node;
      struct acpi_dev_node acpi_node;
      dev_t devt;
      u32 id;
      spinlock_t devres_lock;
      struct list_head devres_head;
      struct klist_node knode_class;
      struct class * class;
      const struct attribute_group ** groups;
      void (* release) (struct device *dev);
      struct iommu_group * iommu_group;
      bool offline_disabled:1;
      bool offline:1;
    };

## Members

parent

  The device's “parent” device, the device to which it is attached. In most cases, a parent device is some sort of bus or host controller. If parent is NULL, the device, is a top-level device, which is not usually what you want.

p

  Holds the private data of the driver core portions of the device. See the comment of the struct device_private for detail.

kobj

  A top-level, abstract class from which other classes are derived.

init_name

  Initial name of the device.

type

  The type of device. This identifies the device type and carries type-specific information.

mutex

  Mutex to synchronize calls to its driver.

bus

  Type of bus device is on.

driver

  Which driver has allocated this

platform_data

  Platform data specific to the device.

power

  For device power management. See Documentation/power/devices.txt for details.

pm_domain

  Provide callbacks that are executed during system suspend, hibernation, system resume and during runtime PM transitions along with subsystem-level and driver-level callbacks.

pins

  For device pin management. See Documentation/pinctrl.txt for details.

numa_node

  NUMA node this device is close to.

dma_mask

  Dma mask (if dma'ble device).

coherent_dma_mask

  Like dma_mask, but for alloc_coherent mapping as not all hardware supports 64-bit addresses for consistent allocations such descriptors.

dma_parms

  A low level driver may set these to teach IOMMU code about segment limitations.

dma_pools

  Dma pools (if dma'ble device).

dma_mem

  Internal for coherent mem override.

cma_area

  Contiguous memory area for dma allocations

archdata

  For arch-specific additions.

of_node

  Associated device tree node.

acpi_node

  Associated ACPI device node.

devt

  For creating the sysfs “dev”.

id

  device instance

devres_lock

  Spinlock to protect the resource of the device.

devres_head

  The resources list of the device.

knode_class

  The node used to add the device to the class list.

class

  The class of the device.

groups

  Optional attribute groups.

release

  Callback to free the device after all references have gone away. This should be set by the allocator of the device (i.e. the bus driver that discovered the device).

iommu_group

  IOMMU group the device belongs to.

offline_disabled

  If set, the device is permanently online.

offline

  Set after successful invocation of bus type's .`offline`.

## Example

       For devices on custom boards, as typical of embedded
       		and SOC based hardware, Linux often uses platform_data to point
       		to board-specific structures describing devices and how they
       		are wired.  That can include what ports are available, chip
       		variants, which GPIO pins act in what additional roles, and so
       		on.  This shrinks the “Board Support Packages” (BSPs) and
       		minimizes board-specific #ifdefs in drivers.

## Description

At the lowest level, every device in a Linux system is represented by an instance of struct device. The device structure contains the information that the device model core needs to model the system. Most subsystems, however, track additional information about the devices they host. As a result, it is rare for devices to be represented by bare device structures; instead, that structure, like kobject structures, is usually embedded within a higher-level representation of the device.

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