pci(4) generic PCI driver


device pci


The driver provides a way for userland programs to read and write PCI configuration registers. It also provides a way for userland programs to get a list of all PCI devices, or all PCI devices that match various patterns.

Since the driver provides a write interface for PCI configuration registers, system administrators should exercise caution when granting access to the device. If used improperly, this driver can allow userland applications to crash a machine or cause data loss.

The driver implements the PCI bus in the kernel. It enumerates any devices on the PCI bus and gives PCI client drivers the chance to attach to them. It assigns resources to children, when the BIOS does not. It takes care of routing interrupts when necessary. It reprobes the unattached PCI children when PCI client drivers are dynamically loaded at runtime.


The device is included in the kernel as described in the SYNOPSIS section. The driver cannot be built as a kld(4).


The following ioctl(2) calls are supported by the driver. They are defined in the header file In sys/pciio.h .

This ioctl(2) takes a pci_conf_io structure. It allows the user to retrieve information on all PCI devices in the system, or on PCI devices matching patterns supplied by the user. The call may set errno to any value specified in either copyin(9) or copyout(9). The pci_conf_io structure consists of a number of fields:

The length, in bytes, of the buffer filled with user-supplied patterns.
The number of user-supplied patterns.
Pointer to a buffer filled with user-supplied patterns. patterns is a pointer to num_patterns pci_match_conf structures. The pci_match_conf structure consists of the following elements:

PCI domain, bus, slot and function.
PCI device driver name.
PCI device driver unit number.
PCI vendor ID.
PCI device ID.
PCI device class.
The flags describe which of the fields the kernel should match against. A device must match all specified fields in order to be returned. The match flags are enumerated in the pci_getconf_flags structure. Hopefully the flag values are obvious enough that they do not need to described in detail.

Length of the matches buffer allocated by the user to hold the results of the PCIOCGETCONF query.
Number of matches returned by the kernel.
Buffer containing matching devices returned by the kernel. The items in this buffer are of type pci_conf which consists of the following items:

PCI domain, bus, slot and function.
PCI header type.
PCI subvendor ID.
PCI subdevice ID.
PCI vendor ID.
PCI device ID.
PCI device class.
PCI device subclass.
PCI device programming interface.
PCI revision ID.
Driver name.
Driver unit number.

The offset is passed in by the user to tell the kernel where it should start traversing the device list. The value passed out by the kernel points to the record immediately after the last one returned. The user may pass the value returned by the kernel in subsequent calls to the PCIOCGETCONF ioctl. If the user does not intend to use the offset, it must be set to zero.
PCI configuration generation. This value only needs to be set if the offset is set. The kernel will compare the current generation number of its internal device list to the generation passed in by the user to determine whether its device list has changed since the user last called the PCIOCGETCONF ioctl. If the device list has changed, a status of PCI_GETCONF_LIST_CHANGED will be passed back.
The status tells the user the disposition of his request for a device list. The possible status values are:

This means that there are no more devices in the PCI device list after the ones returned in the matches buffer.
This status tells the user that the PCI device list has changed since his last call to the PCIOCGETCONF ioctl and he must reset the offset and generation to zero to start over at the beginning of the list.
This tells the user that his buffer was not large enough to hold all of the remaining devices in the device list that possibly match his criteria. It is possible for this status to be returned, even when none of the remaining devices in the list would match the user's criteria.
This indicates a general error while servicing the user's request. If the pat_buf_len is not equal to num_patterns times Fn sizeof struct pci_match_conf , errno will be set to Er EINVAL .

This ioctl(2) reads the PCI configuration registers specified by the passed-in pci_io structure. The pci_io structure consists of the following fields:

A pcisel structure which specifies the domain, bus, slot and function the user would like to query. If the specific bus is not found, errno will be set to ENODEV and -1 returned from the ioctl.
The PCI configuration register the user would like to access.
The width, in bytes, of the data the user would like to read. This value may be either 1, 2, or 4. 3-byte reads and reads larger than 4 bytes are not supported. If an invalid width is passed, errno will be set to EINVAL.
The data returned by the kernel.

This ioctl(2) allows users to write to the PCI specified in the passed-in pci_io structure. The pci_io structure is described above. The limitations on data width described for reading registers, above, also apply to writing PCI configuration registers.


Character device for the driver.


The driver (not the kernel's PCI support code) first appeared in Fx 2.2 , and was written by Stefan Esser and Garrett Wollman. Support for device listing and matching was re-implemented by Kenneth Merry, and first appeared in Fx 3.0 .


An Kenneth Merry Aq [email protected]


It is not possible for users to specify an accurate offset into the device list without calling the PCIOCGETCONF at least once, since they have no way of knowing the current generation number otherwise. This probably is not a serious problem, though, since users can easily narrow their search by specifying a pattern or patterns for the kernel to match against.