Manual browser: pci_conf_read(9)

PCI(9) Kernel Developer's Manual PCI(9)


PCI, pci_activate, pci_bus_devorder, pci_chipset_tag_create, pci_chipset_tag_destroy, pci_conf_read, pci_conf_write, pci_conf_print, pci_conf_capture, pci_conf_restore, pci_find_device, pci_get_capability, pci_mapreg_type, pci_mapreg_map, pci_mapreg_info, pci_intr_map, pci_intr_string, pci_intr_evcnt, pci_intr_establish, pci_intr_disestablish, pci_get_powerstate, pci_set_powerstate, pci_vpd_read, pci_vpd_write, pci_make_tag, pci_decompose_tag, pci_findvendor, pci_devinfo, PCI_VENDOR, PCI_PRODUCT, PCI_REVISIONPeripheral Component Interconnect


#include <sys/bus.h>
#include <dev/pci/pcivar.h>
#include <dev/pci/pcireg.h>
#include <dev/pci/pcidevs.h>

pci_bus_devorder(pci_chipset_tag_t pc, int bus, uint8_t *devs, int maxdevs);

pci_activate(pci_chipset_tag_t pc, pcitag_t tag, device_t dev, int (*wakeup)(pci_chipset_tag_t pc, pcitag_t tag, device_t dev, pcireg_t reg));

pci_chipset_tag_create(pci_chipset_tag_t opc, uint64_t present, const struct pci_overrides *ov, void *ctx, pci_chipset_tag_t *pcp);

pci_chipset_tag_destroy(pci_chipset_tag_t pc);

pci_conf_read(pci_chipset_tag_t pc, pcitag_t tag, int reg);

pci_conf_write(pci_chipset_tag_t pc, pcitag_t tag, int reg, pcireg_t val);

pci_conf_print(pci_chipset_tag_t pc, pcitag_t tag, void (*func)(pci_chipset_tag_t, pcitag_t, const pcireg_t *));

pci_conf_capture(pci_chipset_tag_t pc, pcitag_t tag, struct pci_conf_state *);

pci_conf_restore(pci_chipset_tag_t pc, pcitag_t tag, struct pci_conf_state *);

pci_find_device(struct pci_attach_args *pa, int (*func)(const struct pci_attach_args *));

pci_get_capability(pci_chipset_tag_t pc, pcitag_t tag, int capid, int *offsetp, pcireg_t *valuep);

pci_mapreg_type(pci_chipset_tag_t pc, pcitag_t tag, int reg);

pci_mapreg_map(const struct pci_attach_args *pa, int reg, pcireg_t type, int busflags, bus_space_tag_t *tagp, bus_space_handle_t *handlep, bus_addr_t *basep, bus_size_t *sizep);

pci_mapreg_info(pci_chipset_tag_t pc, pcitag_t tag, int reg, pcireg_t type, bus_addr_t *basep, bus_size_t *sizep, int *flagsp);

pci_find_rom(const struct pci_attach_args *pa, bus_space_tag_t bst, bus_space_handle_t bsh, int code, bus_space_handle_t *handlep, bus_space_size_t *sizep);

pci_intr_map(const struct pci_attach_args *pa, pci_intr_handle_t *ih);

const char *
pci_intr_string(pci_chipset_tag_t pc, pci_intr_handle_t ih);

const struct evcnt *
pci_intr_evcnt(pci_chipset_tag_t pc, pci_intr_handle_t ih);

void *
pci_intr_establish(pci_chipset_tag_t pc, pci_intr_handle_t ih, int level, int (*handler)(void *), void *arg);

pci_intr_disestablish(pci_chipset_tag_t pc, void *ih);

pci_set_powerstate(pci_chipset_tag_t pc, pcitag_t tag, pcireg_t newstate);

pci_get_powerstate(pci_chipset_tag_t pc, pcitag_t tag, pcireg_t *state);

pci_vpd_read(pci_chipset_tag_t pc, pcitag_t tag, int offset, int count, pcireg_t *data);

pci_vpd_write(pci_chipset_tag_t pc, pcitag_t tag, int offset, int count, pcireg_t *data);

pci_make_tag(pci_chipset_tag_t pc, int bus, int device, int function);

pci_decompose_tag(pci_chipset_tag_t pc, pcitag_t tag, int *busp, int *devicep, int *functionp);

char *
pci_findvendor(pcireg_t id);

pci_devinfo(pcireg_t id, pcireg_t class, int show, char *cp, size_t len);

pci_aprint_devinfo(struct pci_attach_args *pa, const char *naive);

PCI_VENDOR(pcireg_t id);

PCI_PRODUCT(pcireg_t id);

PCI_REVISION(pcireg_t id);


The machine-independent PCI subsystem provides support for PCI devices.

The PCI bus was initially developed by Intel in the early 1990's to replace the ISA bus for interfacing with their Pentium processor. The PCI specification is widely regarded as well designed, and the PCI bus has found widespread acceptance in machines ranging from Apple's PowerPC-based systems to Sun's UltraSPARC-based machines.

The PCI bus is a multiplexed bus, allowing addresses and data on the same pins for a reduced number of pins. Data transfers can be 8-bit, 16-bit or 32-bit. A 64-bit extended PCI bus is also defined. Multi-byte transfers are little-endian. The PCI bus operates up to 33MHz and any device on the bus can be the bus master.

AGP is a version of PCI optimised for high-throughput data rates, particularly for accelerated frame buffers.

The PCI bus is a "plug and play" bus, in the sense that devices can be configured dynamically by software. The PCI interface chip on a PCI device bus presents a small window of registers into the PCI configuration space. These registers contain information about the device such as the vendor and a product ID. The configuration registers can also be written to by software to alter how the device interfaces to the PCI bus. An important register in the configuration space is the Base Address Register (BAR). The BAR is written to by software to map the device registers into a window of processor address space. Once this mapping is done, the device registers can be accessed relative to the base address.


Drivers for devices attached to the PCI will make use of the following data types:
Configuration space register.
Chipset tag for the PCI bus.
Configuration tag describing the location and function of the PCI device. It contains the tuple <bus, device, function>.
The opaque handle describing an established interrupt handler.
struct pci_attach_args
Devices have their identity recorded in this structure. It contains the following members:

	bus_space_tag_t pa_iot;		/* pci i/o space tag */ 
	bus_space_tag_t pa_memt;	/* pci mem space tag */ 
	bus_dma_tag_t pa_dmat;		/* DMA tag */ 
	pci_chipset_tag_t pa_pc; 
	int pa_flags;			/* flags */ 
	pcitag_t pa_tag; 
	pcireg_t pa_id; 
	pcireg_t pa_class;
struct pci_conf_state
Stores the PCI configuration state of a device. It contains the following member:

	pcireg_t reg[16];			/* pci conf register */
struct pci_overrides
Stores pointers to functions that override the architecture's default pci(9) and pci_intr(9) implementation. It contains the following members:

	pcireg_t (*ov_conf_read)(void *, 
	    pci_chipset_tag_t, pcitag_t, int); 
	void (*ov_conf_write)(void *, 
	    pci_chipset_tag_t, pcitag_t, int, pcireg_t); 
	int (*ov_intr_map)(void *, 
	   const struct pci_attach_args *, pci_intr_handle_t *); 
	const char *(*ov_intr_string)(void *, 
	    pci_chipset_tag_t, pci_intr_handle_t); 
	const struct evcnt *(*ov_intr_evcnt)(void *, 
	    pci_chipset_tag_t, pci_intr_handle_t); 
	void *(*ov_intr_establish)(void *, 
	    pci_chipset_tag_t, pci_intr_handle_t, 
	    int, int (*)(void *), void *); 
	void (*ov_intr_disestablish)(void *, 
	    pci_chipset_tag_t, void *); 
	pcitag_t (*ov_make_tag)(void *, 
	    pci_chipset_tag_t, int, int, int); 
	void (*ov_decompose_tag)(void *, 
	    pci_chipset_tag_t, pcitag_t, int *, int *, int *);


pci_bus_devorder(pc, bus, devs, maxdevs)
Tell how many devices a PCI bus driver should probe and in what order. If maxdevs is less than or equal to zero, return 0 and do not modify devs. Otherwise, return maxdevs or the number of devices on bus to probe, whichever is less, and copy to devs each of the PCI device numbers to probe in the order that they should be probed. pci_bus_devorder() will not copy more than maxdevs device numbers to devs.
pci_activate(pc, tag, dev, fun)
Attempt to bring the device to state D0. If the device is not in the D0 state call fun to restore its state. If fun is NULL then restoring from state D3 is going to fail.
pci_chipset_tag_create(opc, present, ov, ctx, pcp)
Create a copy of the tag opc at *pcp. Except for the behavior overridden by ov, *pcp inherits the behavior of opc under PCI calls.

ov contains function pointers corresponding to PCI routines. Each function pointer has a corresponding bit in present, and if that bit is 1, the function pointer overrides the corresponding PCI call for the new tag. Any combination of these bits may be set in present:


pci_chipset_tag_create() does not copy ov. After a new tag is created by pci_chipset_tag_create(), ov must not be destroyed until after the tag is destroyed by pci_chipset_tag_destroy().

The first argument of every override-function is a void *, and ctx is passed in that argument.

Return 0 if the call succeeds. Return EOPNOTSUPP if the architecture does not support overrides. Return EINVAL if present is 0, if ov is NULL, or if present indicates that an override is present, but the corresponding override in ov is NULL.

If the call does not succeed, *pcp is undefined.

Destroy a tag, pc, created by a prior call to pci_chipset_tag_create(). If pc was not created by pci_chipset_tag_create(), results are undefined. If pc was already destroyed, results are undefined.
pci_conf_read(pc, tag, reg)
Read from register reg in PCI configuration space. The argument tag is the PCI tag for the current device attached to PCI chipset pc.
pci_conf_write(pc, tag, reg, val)
Write to register reg in PCI configuration space. The argument tag is the PCI tag for the current device attached to PCI chipset pc.
pci_conf_print(pc, tag, func)
Print out most of the registers in the PCI configuration for the device. The argument tag is the PCI tag for the current device attached to PCI chipset pc. The argument func is a function called by pci_conf_print() to print the device-dependent registers. This function is only useful for driver development and is usually wrapped in pre-processor declarations.
pci_conf_capture(pc, tag, pcs)
Capture PCI configuration space into structure pcs. The argument tag is the PCI tag for the current device attached to the PCI chipset pc.
pci_conf_restore(pc, tag, pcs)
Restores PCI configuration space from structure pcs. The argument tag is the PCI tag for the current device attached to the PCI chipset pc.
pci_find_device(pa, func)
Find a device using a match function on all probed busses. The argument func is called by pci_find_device() to match a device. The argument pa is filled in if the device is matched. pci_find_device() returns 1 if the device is matched, and zero otherwise. This function is specifically for use by kernel modules and its use otherwise is strongly discouraged.
pci_get_capability(pc, tag, capid, offsetp, valuep)
Parse the device capability list in configuration space looking for capability capid. If offsetp is not NULL, the register offset in configuration space is returned in offsetp. If valuep is not NULL, the value of the capability is returned in valuep. The argument tag is the PCI tag for the current device attached to PCI chipset pc. This function returns 1 if the capability was found. If the capability was not found, it returns zero, and offsetp and valuep remain unchanged.
pci_mapreg_type(pc, tag, reg)
Interrogates the Base Address Register (BAR) in configuration space specified by reg and returns the default (or current) mapping type. Valid returns values are:
The mapping is to I/O address space.
The mapping is to memory address space.
The mapping is to 64-bit memory address space.
The mapping is to ROM. Note that in the current implementation, PCI_MAPREG_TYPE_ROM has the same numeric value as PCI_MAPREG_TYPE_MEM.

The argument tag is the PCI tag for the current device attached to PCI chipset pc.

pci_mapreg_map(pa, reg, type, busflags, tagp, handlep, basep, sizep)
Maps the register windows for the device into kernel virtual address space. This function is generally only called during the driver attach step and takes a pointer to the struct pci_attach_args in pa. The physical address of the mapping is in the Base Address Register (BAR) in configuration space specified by reg. Valid values for the type of mapping type are:
The mapping should be to I/O address space.
The mapping should be to memory address space.
The mapping is to access ROM. This type of mapping is only permitted when the value for reg is PCI_MAPREG_ROM.

The argument busflags are bus-space flags passed to bus_space_map() to perform the mapping (see bus_space(9)). The bus-space tag and handle for the mapped register window are returned in tagp and handlep respectively. The bus-address and size of the mapping are returned in basep and sizep respectively. If any of tagp, handlep, basep, or sizep are NULL then pci_mapreg_map() does not define their return value. This function returns zero on success and non-zero on error.

pci_mapreg_info(pc, tag, reg, type, basep, sizep, flagsp)
Performs the same operations as pci_mapreg_map() but doesn't actually map the register window into kernel virtual address space. Returns the bus-address, size and bus flags in basep, sizep and flagsp respectively. These return values can be used by bus_space_map() to actually map the register window into kernel virtual address space. This function is useful for setting up the registers in configuration space and deferring the mapping to a later time, such as in a bus-independent attachment routine. pci_mapreg_info returns zero on success and non-zero on failure.
pci_find_rom(pa, bst, bsh, code, handlep, sizep)
Locates a suitable ROM image within a PCI expansion ROM previously mapped with pci_mapreg_map() and creates a subregion for it with bus_space_subregion(). The bst and bsh arguments are the bus tag and handle obtained with the prior call to pci_mapreg_map(). Valid values for the image type code are:
Find a ROM image containing i386 executable code for use by PC BIOS.
Find a ROM image containing Forth code for use by Open Firmware.
Find a ROM image containing HP PA/RISC executable code.

The created subregion will cover the entire selected ROM image, including header data. The handle to this subregion is returned in handlep. The size of the image (and the corresponding subregion) is returned in sizep. This function can only be used with expansion ROMs located at the PCI_MAPREG_ROM base address register (BAR).

pci_intr_map(pa, ih)
See pci_intr(9).
pci_intr_string(pc, ih)
See pci_intr(9).
pci_intr_evcnt(pc, ih)
See pci_intr(9).
pci_intr_establish(pc, ih, level, handler, arg)
See pci_intr(9).
pci_intr_disestablish(pc, ih)
See pci_intr(9).
pci_set_powerstate(pc, tag, newstate)
Set power state of the device to newstate. Valid values for newstate are:

pci_get_powerstate(pc, tag, state)
Get current power state of the device.
pci_vpd_read(pc, tag, offset, count, data)
Read count 32-bit words of Vital Product Data for the device starting at offset offset into the buffer pointed to by data. Returns 0 on success or non-zero if the device has no Vital Product Data capability or if reading the Vital Product Data fails.
pci_vpd_write(pc, tag, offset, count, data)
Write count 32-bit words of Vital Product Data for the device starting at offset offset from the buffer pointed to by data. Returns 0 on success or non-zero if the device has no Vital Product Data capability of if writing the Vital Product Data fails.
pci_make_tag(pc, bus, device, function)
Create a new PCI tag for the PCI device specified by the tuple <bus, device, function>. This function is not useful to the usual PCI device driver. It is generally used by drivers of multi-function devices when attaching other PCI device drivers to each function.
pci_decompose_tag(pc, tag, busp, devicep, fnp)
Decompose the PCI tag tag generated by pci_make_tag() into its <bus, device, function> tuple.
Return the string of the vendor name for the device specified by id.
pci_devinfo(id, class, show, cp, len)
Returns the description string from the in-kernel PCI database for the device described by id and class. The description string is returned in cp; the size of that storage is given in len. The argument show specifies whether the PCI subsystem should report the string to the console.
pci_aprint_devinfo(pa, naive)
Print device information to the console and system log, using the aprint_normal(9) and aprint_naive(9) functions. For the device information, the “pci_devinfo” function above is used, or the naive argument in the “AB_QUIET” case. This function is intended to be used early in device attach.
Return the PCI vendor id for device id.
Return the PCI product id for device id.
Return the PCI product revision for device id.


During autoconfiguration, a PCI driver will receive a pointer to struct pci_attach_args describing the device attaches to the PCI bus. Drivers match the device using the pa_id member using PCI_VENDOR(). PCI_PRODUCT() and PCI_REVISION().

During the driver attach step, drivers can read the device configuration space using pci_conf_read(). The meaning attached to registers in the PCI configuration space are device-dependent, but will usually contain physical addresses of the device register windows. Device options can also be stored into the PCI configuration space using pci_conf_write(). For example, the driver can request support for bus-mastering DMA by writing the option to the PCI configuration space.

Device capabilities can be queried using pci_get_capability(), and returns device-specific information which can be found in the PCI configuration space to alter device operation.

After reading the physical addresses of the device register windows from configuration space, these windows must be mapped into kernel virtual address space using pci_mapreg_map(). Device registers can now be accessed using the standard bus-space API (see bus_space(9)).

Details of using PCI interrupts is described in pci_intr(9).


The PCI bus supports bus-mastering operations from any device on the bus. The DMA facilities are accessed through the standard bus_dma(9) interface. To support DMA transfers from the device to the host, it is necessary to enable bus-mastering in the PCI configuration space for the device.

During system shutdown, it is necessary to abort any DMA transfers in progress by registering a shutdown hook (see pmf(9)).


The PCI subsystem itself is implemented within the files sys/dev/pci/pci.c, sys/dev/pci/pci_subr.c, sys/dev/pci/pci_map.c, sys/dev/pci/pci_quirks.c, and sys/dev/pci/pciconf.c. Machine-dependent portions are implemented within the file sys/arch/<arch>/pci/pci_machdep.c.

The database of known devices exists within the file sys/dev/pci/pcidevs_data.h and is generated automatically from the file sys/dev/pci/pcidevs. New vendor and product identifiers should be added to this file. The database can be regenerated using the Makefile sys/dev/pci/Makefile.pcidevs.


The machine-independent PCI subsystem appeared in NetBSD 1.2.
January 30, 2012 NetBSD 7.0