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     bus_activate_resource, bus_deactivate_resource — activate or deactivate a resource


     #include <sys/param.h>
     #include <sys/bus.h>

     #include <machine/bus.h>
     #include <sys/rman.h>
     #include <machine/resource.h>

     bus_activate_resource(device_t dev, int type, int rid, struct resource *r);

     bus_deactivate_resource(device_t dev, int type, int rid, struct resource *r);


     These functions activate or deactivate a previously allocated resource.  In general,
     resources must be activated before they can be accessed by the driver.  Bus drivers may
     perform additional actions to ensure that the resource is ready to be accessed.  For
     example, the PCI bus driver enables memory decoding in a PCI device's command register when
     activating a memory resource.

     The arguments are as follows:

     dev     The device that requests ownership of the resource.  Before allocation, the resource
             is owned by the parent bus.

     type    The type of resource you want to allocate.  It is one of:

             PCI_RES_BUS     for PCI bus numbers
             SYS_RES_IRQ     for IRQs
             SYS_RES_DRQ     for ISA DMA lines
             SYS_RES_IOPORT  for I/O ports
             SYS_RES_MEMORY  for I/O memory

     rid     A pointer to a bus specific handle that identifies the resource being allocated.

     r       A pointer to the struct resource returned by bus_alloc_resource(9).

   Resource Mapping
     Resources which can be mapped for CPU access by a bus_space(9) tag and handle will create a
     mapping of the entire resource when activated.  The tag and handle for this mapping are
     stored in r and can be retrieved via rman_get_bustag(9) and rman_get_bushandle(9).  These
     can be used with the bus_space(9) API to access device registers or memory described by r.
     If the mapping is associated with a virtual address, the virtual address can be retrieved
     via rman_get_virtual(9).

     This implicit mapping can be disabled by passing the RF_UNMAPPED flag to
     bus_alloc_resource(9).  A driver may use this if it wishes to allocate its own mappings of a
     resource using bus_map_resource(9).

     A wrapper API for bus_space(9) is also provided that accepts the associated resource as the
     first argument in place of the bus_space(9) tag and handle.  The functions in this wrapper
     API are named similarly to the bus_space(9) API except that “_space” is removed from their
     name.  For example, bus_read_4() can be used in place of bus_space_read_4().  The wrapper
     API is preferred in new drivers.

     These two statements both read a 32-bit register at the start of a resource:

             bus_space_read_4(rman_get_bustag(res), rman_get_bushandle(res), 0);
             bus_read_4(res, 0);


     Zero is returned on success, otherwise an error is returned.


     bus_alloc_resource(9), bus_map_resource(9), bus_space(9), device(9), driver(9)


     This manual page was written by Warner Losh <>.