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PCI(4)                 FreeBSD Kernel Interfaces Manual                 PCI(4)

     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 loss.

     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

     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

                                     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

                                     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

                                     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

                      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 EINVAL.

     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 fields:

                      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 ioctl.

                      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.

     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

     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

             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

     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 `D'.

             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.

     /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 <[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

FreeBSD 11.1-RELEASE-p4        September 8, 2016       FreeBSD 11.1-RELEASE-p4
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