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     pci — generic PCI driver


     device pci


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

     The pci 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


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


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

     PCIOCGETCONF     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:

                      pat_buf_len    The length, in bytes, of the buffer filled with user-
                                     supplied patterns.

                      num_patterns   The number of user-supplied patterns.

                      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:

                                     pc_sel     PCI domain, bus, slot and function.

                                     pd_name    PCI device driver name.

                                     pd_unit    PCI device driver unit number.

                                     pc_vendor  PCI vendor ID.

                                     pc_device  PCI device ID.

                                     pc_class   PCI device class.

                                     flags      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.

                      match_buf_len  Length of the matches buffer allocated by the user to hold
                                     the results of the PCIOCGETCONF query.

                      num_matches    Number of matches returned by the kernel.

                      matches        Buffer containing matching devices returned by the kernel.
                                     The items in this buffer are of type pci_conf, which
                                     consists of the following items:

                                     pc_sel        PCI domain, bus, slot and function.

                                     pc_hdr        PCI header type.

                                     pc_subvendor  PCI subvendor ID.

                                     pc_subdevice  PCI subdevice ID.

                                     pc_vendor     PCI vendor ID.

                                     pc_device     PCI device ID.

                                     pc_class      PCI device class.

                                     pc_subclass   PCI device subclass.

                                     pc_progif     PCI device programming interface.

                                     pc_revid      PCI revision ID.

                                     pd_name       Driver name.

                                     pd_unit       Driver unit number.

                      offset         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.

                      generation     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.

                      status         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 sizeof(struct pci_match_conf), errno will be set to

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

                      pi_sel    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

                      pi_reg    The PCI configuration register the user would like to access.

                      pi_width  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.

                      pi_data   The data returned by the kernel.

     PCIOCWRITE       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.


     /dev/pci  Character device for the pci driver.




     The pci driver (not the kernel's PCI support code) first appeared in FreeBSD 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 FreeBSD 3.0.


     Kenneth Merry <>


     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