As part of configuring and operating devices, a driver might need to manage hardware resources, such as interrupt-request lines (IRQs), I/O ports, or I/O memory (McKusick and Neville-Neil, 2005). Naturally, Newbus includes several functions for doing just that.
#include <sys/param.h>
#include <sys/bus.h>
#include <machine/bus.h>
#include <sys/rman.h>
#include <machine/resource.h>
struct resource *
bus_alloc_resource(device_t dev, int type, int *rid, u_long start,
u_long end, u_long count, u_int flags);
struct resource *
bus_alloc_resource_any(device_t dev, int type, int *rid,
u_int flags);
int
bus_activate_resource(device_t dev, int type, int rid,
struct resource *r);
int
bus_deactivate_resource(device_t dev, int type, int rid,
struct resource *r);
int
bus_release_resource(device_t dev, int type, int rid,
struct resource *r);The bus_alloc_resource function allocates hardware resources for a specific device to use. If successful, a struct resource pointer is returned; otherwise, NULL is returned. This function is normally called during device_attach. If it is called during device_probe, all allocated resources must be released (via bus_release_resource) before returning. Most of the arguments for bus_alloc_resource are common to the other hardware resource management functions. These arguments are described in the next few paragraphs.
The dev argument is the device that requires ownership of the hardware resource(s). Before allocation, resources are owned by the parent bus.
The type argument represents the type of resource dev wants allocated. Valid values for this argument are listed in Table 7-2.
Table 7-2. Symbolic Constants for Hardware Resources
Constant | Description |
|---|---|
| Interrupt-request line |
| I/O port |
| I/O memory |
The rid argument expects a resource ID (RID). If bus_alloc_resource is successful, a RID is returned in rid that may differ from what you passed. You’ll learn more about RIDs later.
The start and end arguments are the start and end addresses of the hardware resource(s). To employ the default bus values, simply pass 0ul as start and ˜0ul as end.
The count argument denotes the size of the hardware resource(s). If you used the default bus values for start and end, count is used only if it is larger than the default bus value.
The flags argument details the characteristics of the hardware resource. Valid values for this argument are listed in Table 7-3.
Table 7-3. bus_alloc_resource Symbolic Constants
Constant | Description |
|---|---|
| Allocate hardware resource, but don’t activate it |
| Allocate hardware resource and activate resource automatically |
| Hardware resource permits contemporaneous sharing; you should always set this flag, unless the resource cannot be shared |
| Hardware resource permits time-division sharing |
The bus_alloc_resource_any function is a convenience wrapper for bus_alloc_resource that sets start, end, and count to their default bus values.
The bus_activate_resource function activates a previously allocated hardware resource. Naturally, resources must be activated before they can be used. Most drivers simply pass RF_ACTIVE to bus_alloc_resource or bus_alloc_resource_any to avoid calling bus_activate_resource.
The bus_deactivate_resource function deactivates a hardware resource. This function is primarily used in bus drivers (so we’ll never call it).
The bus_release_resource function releases a previously allocated hardware resource. Of course, the resource cannot be in use on release. If successful, 0 is returned; otherwise, the kernel panics.
Note
We’ll cover an example that employs IRQs in Chapter 8 and Chapter 9, and I’ll go over an example that requires I/O ports and I/O memory in Chapter 10 and Chapter 11.