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NAME
pci — generic PCI bus driver
SYNOPSIS
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
DESCRIPTION
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 adapters.
IOCTLS
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:
PCI_GETCONF_LAST_DEVICE
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.
PCI_GETCONF_LIST_CHANGED
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.
PCI_GETCONF_MORE_DEVS
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.
PCI_GETCONF_ERROR
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 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 them.
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
reads.
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.
LOADER TUNABLES
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.
hw.pci<D>.<B>.<S>.INT<P>.irq
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.
DEVICE WIRING
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.
Examples
Given the following lines in /boot/device.hints: hint.nvme.3.at="pci6:0:0" hint.igb.8.at="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.
FILES
/dev/pci Character device for the pci driver.
SEE ALSO
pciconf(8)
HISTORY
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.
AUTHORS
Kenneth Merry <ken@FreeBSD.org>
BUGS
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.
Debian June 17, 2019 PCI(4)