Writing Device Drivers

ddi_device_acc_attr Structure

This structure describes the endian and data order requirements of the device. The driver is required to initialize and pass this structure as an argument to ddi_regs_map_setup(9F).

typedef struct ddi_device_acc_attr {
    ushort_t       devacc_attr_version;
    uchar_t    devacc_attr_endian_flags;
    uchar_t    devacc_attr_dataorder;
} ddi_device_acc_attr_t;



Describes the endian characteristics of the device. Specified as a bit value whose possible values are:

  • DDI_NEVERSWAP_ACC – Never swap data

  • DDI_STRUCTURE_BE_ACC – The device data format is big-endian

  • DDI_STRUCTURE_LE_ACC – The device data format is little-endian


Describes the order in which the CPU must reference data as required by the device. Specified as an enumerated value, where data access restrictions are ordered from most strict to least strict.

  • DDI_STRICTORDER_ACC – The host must issue the references in order, as specified by the programmer. This flag is the default behavior.

  • DDI_UNORDERED_OK_ACC – The host is allowed to reorder loads and stores to device memory.

  • DDI_MERGING_OK_ACC – The host is allowed to merge individual stores to consecutive locations. This setting also implies reordering.

  • DDI_LOADCACHING_OK_ACC – The host is allowed to read data from the device until a store occurs.

  • DDI_STORECACHING_OK_ACC – The host is allowed to cache data written to the device. The host can then defer writing the data to the device until a future time.

Note –

The system can access data more strictly than the driver specifies in devacc_attr_dataorder. The restriction to the host diminishes while moving from strict data ordering to cache storing in terms of data accesses by the driver.