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     pci — generic PCI bus driver


     To compile the PCI bus driver into the kernel, place the following line in your kernel
     configuration file:

           device pci

     To compile in support for Single Root I/O Virtualization (SR-IOV):

           options PCI_IOV

     To compile in support for native PCI-express HotPlug:

           options PCI_HP


     The pci driver provides support for PCI devices in the kernel and limited access to PCI
     devices for userland.

     The pci driver provides a /dev/pci character device that can be used by userland programs to
     read and write PCI configuration registers.  Programs can also use this device 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
     runtime.  The pci driver also includes support for PCI-PCI bridges, various platform-
     specific Host-PCI bridges, and basic support for PCI VGA adapters.


     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 matching the specified criteria 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
                                     match his 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 registers 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 configuration registers
                      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.

     PCIOCATTACHED    This ioctl(2) allows users to query if a driver is attached to the PCI
                      device specified in the passed-in pci_io structure.  The pci_io structure
                      is described above, however, the pi_reg and pi_width fields are not used.
                      The status of the device is stored in the pi_data field.  A value of 0
                      indicates no driver is attached, while a value larger than 0 indicates that
                      a driver is attached.

     PCIOCBARMMAP     This ioctl(2) command allows userspace processes to mmap(2) the memory-
                      mapped PCI BAR into its address space.  The input parameters and results
                      are passed in the pci_bar_mmap structure, which has the following fields:

                      uint64_t  pbm_map_base
                                Reports the established mapping base to the caller.  If
                                PCIIO_BAR_MMAP_FIXED flag was specified, then this field must be
                                filled before the call with the desired address for the mapping.

                      uint64_t pbm_map_length
                                Reports the mapped length of the BAR, in bytes.  Its .Vt uint64_t
                                value is always multiple of machine pages.

                      int64_t pbm_bar_length
                                Reports length of the bar as exposed by the device.

                      int pbm_bar_off
                                Reports offset from the mapped base to the start of the first
                                register in the bar.

                      struct pcisel pbm_sel
                                Should be filled before the call.  Describes the device to
                                operate on.

                      int pbm_reg
                                The BAR index to mmap.

                      int pbm_flags
                                Flags which augments the operation.  See below.

                      int pbm_memattr
                                The caching attribute for the mapping.  Typical values are
                                VM_MEMATTR_UNCACHEABLE for control registers BARs, and
                                VM_MEMATTR_WRITE_COMBINING for frame buffers.  Regular memory-
                                like BAR should be mapped with VM_MEMATTR_DEFAULT attribute.

                      Currently defined flags are:

                      PCIIO_BAR_MMAP_FIXED     The resulted mappings should be established at the
                                               address specified by the pbm_map_base member,
                                               otherwise fail.

                      PCIIO_BAR_MMAP_EXCL      Must be used together with If the specified base
                                               contains already established mappings, the
                                               operation fails instead of implicitly unmapping

                      PCIIO_BAR_MMAP_RW        The requested mapping allows both reading and
                                               writing.  Without the flag, read-only mapping is
                                               established.  Note that it is common for the
                                               device registers to have side-effects even on

                      PCIIO_BAR_MMAP_ACTIVATE  (Unimplemented) If the BAR is not activated,
                                               activate it in the course of mapping.  Currently
                                               attempt to mmap an inactive BAR results in error.


     Tunables can be set at the loader(8) prompt before booting the kernel, or stored in
     loader.conf(5).  The current value of these tunables can be examined at runtime via
     sysctl(8) nodes of the same name.  Unless otherwise specified, each of these tunables is a
     boolean that can be enabled by setting the tunable to a non-zero value.

     hw.pci.clear_bars (Defaults to 0)
             Ignore any firmware-assigned memory and I/O port resources.  This forces the PCI bus
             driver to allocate resource ranges for memory and I/O port resources from scratch.

     hw.pci.clear_buses (Defaults to 0)
             Ignore any firmware-assigned bus number registers in PCI-PCI bridges.  This forces
             the PCI bus driver and PCI-PCI bridge driver to allocate bus numbers for secondary
             buses behind PCI-PCI bridges.

     hw.pci.clear_pcib (Defaults to 0)
             Ignore any firmware-assigned memory and I/O port resource windows in PCI-PCI
             bridges.  This forces the PCI-PCI bridge driver to allocate memory and I/O port
             resources for resource windows from scratch.

             By default the PCI-PCI bridge driver will allocate windows that contain the
             firmware-assigned resources devices behind the bridge.  In addition, the PCI-PCI
             bridge driver will suballocate from existing window regions when possible to satisfy
             a resource request.  As a result, both hw.pci.clear_bars and hw.pci.clear_pcib must
             be enabled to fully ignore firmware-supplied resource assignments.

     hw.pci.default_vgapci_unit (Defaults to -1)
             By default, the first PCI VGA adapter encountered by the system is assumed to be the
             boot display device.  This tunable can be set to choose a specific VGA adapter by
             specifying the unit number of the associated vgapciX device.

     hw.pci.do_power_nodriver (Defaults to 0)
             Place devices into a low power state (D3) when a suitable device driver is not
             found.  Can be set to one of the following values:

             3       Powers down all PCI devices without a device driver.

             2       Powers down most devices without a device driver.  PCI devices with the
                     display, memory, and base peripheral device classes are not powered down.

             1       Similar to a setting of 2 except that storage controllers are also not
                     powered down.

             0       All devices are left fully powered.

             A PCI device must support power management to be powered down.  Placing a device
             into a low power state may not reduce power consumption.

     hw.pci.do_power_resume (Defaults to 1)
             Place PCI devices into the fully powered state when resuming either the system or an
             individual device.  Setting this to zero is discouraged as the system will not
             attempt to power up non-powered PCI devices after a suspend.

     hw.pci.do_power_suspend (Defaults to 1)
             Place PCI devices into a low power state when suspending either the system or
             individual devices.  Normally the D3 state is used as the low power state, but
             firmware may override the desired power state during a system suspend.

     hw.pci.enable_ari (Defaults to 1)
             Enable support for PCI-express Alternative RID Interpretation.  This is often used
             in conjunction with SR-IOV.

     hw.pci.enable_io_modes (Defaults to 1)
             Enable memory or I/O port decoding in a PCI device's command register if it has
             firmware-assigned memory or I/O port resources.  The firmware (BIOS) in some systems
             does not enable memory or I/O port decoding for some devices even when it has
             assigned resources to the device.  This enables decoding for such resources during
             bus probe.

     hw.pci.enable_msi (Defaults to 1)
             Enable support for Message Signalled Interrupts (MSI).  MSI interrupts can be
             disabled by setting this tunable to 0.

     hw.pci.enable_msix (Defaults to 1)
             Enable support for extended Message Signalled Interrupts (MSI-X).  MSI-X interrupts
             can be disabled by setting this tunable to 0.

     hw.pci.enable_pcie_hp (Defaults to 1)
             Enable support for native PCI-express HotPlug.

     hw.pci.honor_msi_blacklist (Defaults to 1)
             MSI and MSI-X interrupts are disabled for certain chipsets known to have broken MSI
             and MSI-X implementations when this tunable is set.  It can be set to zero to permit
             use of MSI and MSI-X interrupts if the chipset match is a false positive.

     hw.pci.iov_max_config (Defaults to 1MB)
             The maximum amount of memory permitted for the configuration parameters used when
             creating Virtual Functions via SR-IOV.  This tunable can also be changed at runtime
             via sysctl(8).

     hw.pci.realloc_bars (Defaults to 0)
             Attempt to allocate a new resource range during the initial device scan for any
             memory or I/O port resources with firmware-assigned ranges that conflict with
             another active resource.

     hw.pci.usb_early_takeover (Defaults to 1 on amd64 and i386)
             Disable legacy device emulation of USB devices during the initial device scan.  Set
             this tunable to zero to use USB devices via legacy emulation when using a custom
             kernel without USB controller drivers.

             These tunables can be used to override the interrupt routing for legacy PCI INTx
             interrupts.  Unlike other tunables in this list, these do not have corresponding
             sysctl nodes.  The tunable name includes the address of the PCI device as well as
             the pin of the desired INTx IRQ to override:

             <D>     The domain (or segment) of the PCI device in decimal.

             <B>     The bus address of the PCI device in decimal.

             <S>     The slot of the PCI device in decimal.

             <P>     The interrupt pin of the PCI slot to override.  One of ‘A’, ‘B’, ‘C’, or

             The value of the tunable is the raw IRQ value to use for the INTx interrupt pin
             identified by the tunable name.  Mapping of IRQ values to platform interrupt sources
             is machine dependent.


     You can wire the device unit at a given location with device.hints.  Entries of the form
     hints.<name>.<unit>.at="pci<B>:<S>:<F>" or hints.<name>.<unit>.at="pci<D>:<B>:<S>:<F>" will
     force the driver name to probe and attach at unit unit for any PCI device found to match the
     specification, where:

     <D>      The domain (or segment) of the PCI device in decimal.  Defaults to 0 if unspecified

     <B>      The bus address of the PCI device in decimal.

     <S>      The slot of the PCI device in decimal.

     <F>      The function of the PCI device in decimal.

     The code to do the matching requires an exact string match.  Do not specify the angle
     brackets (< >) in the hints file.  Wiring multiple devices to the same name and unit
     produces undefined results.

     Given the following lines in /boot/device.hints:"pci6:0:0""pci14:0:0" If there is a device that supports igb(4) at PCI bus 14 slot 0
     function 0, then it will be assigned igb8 for probe and attach.  Likewise, if there is an
     nvme(4) card at PCI bus 6 slot 0 function 0, then it will be assigned nvme3 for probe and
     attach.  If another type of card is in either of these locations, the name and unit of that
     card will be the default names and will be unaffected by these hints.  If other igb or nvme
     cards are located elsewhere, they will be assigned their unit numbers sequentially, skipping
     the unit numbers that have 'at' hints.


     /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