Raw Configuration Access¶

The pci_read_config() function is used to read data from the PCI configuration space of the device dev, at offset reg, with width specifying the size of the access.

The pci_write_config() function is used to write the value val to the PCI configuration space of the device dev, at offset reg, with width specifying the size of the access.

The pcie_adjust_config() function is used to modify the value of a register in the PCI-express capability register set of device dev. The offset reg specifies a relative offset in the register set with width specifying the size of the access. The new value of the register is computed by modifying bits set in mask to the value in val. Any bits not specified in mask are preserved. The previous value of the register is returned.

The pcie_read_config() function is used to read the value of a register in the PCI-express capability register set of device dev. The offset reg specifies a relative offset in the register set with width specifying the size of the access.

The pcie_write_config() function is used to write the value val to a register in the PCI-express capability register set of device dev. The offset reg specifies a relative offset in the register set with width specifying the size of the access.

NOTE: Device drivers should only use these functions for functionality that is not available via another pci() function.

Locating Devices¶

The pci_find_bsf() function looks up the device_t of a PCI device, given its bus, slot, and func. The slot number actually refers to the number of the device on the bus, which does not necessarily indicate its geographic location in terms of a physical slot. Note that in case the system has multiple PCI domains, the pci_find_bsf() function only searches the first one. Actually, it is equivalent to:

pci_find_dbsf(0, bus, slot, func);

The pci_find_dbsf() function looks up the device_t of a PCI device, given its domain, bus, slot, and func. The slot number actually refers to the number of the device on the bus, which does not necessarily indicate its geographic location in terms of a physical slot.

The pci_find_device() function looks up the device_t of a PCI device, given its vendor and device IDs. Note that there can be multiple matches for this search; this function only returns the first matching device.

Device Information¶

The pci_find_cap() function is used to locate the first instance of a PCI capability register set for the device dev. The capability to locate is specified by ID via capability. Constant macros of the form PCIY_xxx for standard capability IDs are defined in <dev/pci/pcireg.h>. If the capability is found, then *capreg is set to the offset in configuration space of the capability register set, and pci_find_cap() returns zero. If the capability is not found or the device does not support capabilities, pci_find_cap() returns an error.

The pci_find_extcap() function is used to locate the first instance of a PCI-express extended capability register set for the device dev. The extended capability to locate is specified by ID via capability. Constant macros of the form PCIZ_xxx for standard extended capability IDs are defined in <dev/pci/pcireg.h>. If the extended capability is found, then *capreg is set to the offset in configuration space of the extended capability register set, and pci_find_extcap() returns zero. If the extended capability is not found or the device is not a PCI-express device, pci_find_extcap() returns an error.

The pci_find_htcap() function is used to locate the first instance of a HyperTransport capability register set for the device dev. The capability to locate is specified by type via capability. Constant macros of the form PCIM_HTCAP_xxx for standard HyperTransport capability types are defined in <dev/pci/pcireg.h>. If the capability is found, then *capreg is set to the offset in configuration space of the capability register set, and pci_find_htcap() returns zero. If the capability is not found or the device is not a HyperTransport device, pci_find_htcap() returns an error.

The pci_find_pcie_root_port() function walks up the PCI device hierarchy to locate the PCI-express root port upstream of dev. If a root port is not found, pci_find_pcie_root_port() returns NULL.

The pci_get_id() function is used to read an identifier from a device. The type flag is used to specify which identifier to read. The following flags are supported:

PCI_ID_RID

Read the routing identifier for the device.

PCI_ID_MSI

Read the MSI routing ID. This is needed by some interrupt controllers to route MSI and MSI-X interrupts.

The pci_get_vpd_ident() function is used to fetch a device's Vital Product Data (VPD) identifier string. If the device dev supports VPD and provides an identifier string, then *identptr is set to point at a read-only, null-terminated copy of the identifier string, and pci_get_vpd_ident() returns zero. If the device does not support VPD or does not provide an identifier string, then pci_get_vpd_ident() returns an error.

The pci_get_vpd_readonly() function is used to fetch the value of a single VPD read-only keyword for the device dev. The keyword to fetch is identified by the two character string kw. If the device supports VPD and provides a read-only value for the requested keyword, then *vptr is set to point at a read-only, null-terminated copy of the value, and pci_get_vpd_readonly() returns zero. If the device does not support VPD or does not provide the requested keyword, then pci_get_vpd_readonly() returns an error.

Device Configuration¶

The pci_enable_busmaster() function enables PCI bus mastering for the device dev, by setting the PCIM_CMD_BUSMASTEREN bit in the PCIR_COMMAND register. The pci_disable_busmaster() function clears this bit.

The pci_enable_io() function enables memory or I/O port address decoding for the device dev, by setting the PCIM_CMD_MEMEN or PCIM_CMD_PORTEN bit in the PCIR_COMMAND register appropriately. The pci_disable_io() function clears the appropriate bit. The space argument specifies which resource is affected; this can be either SYS_RES_MEMORY or SYS_RES_IOPORT as appropriate. Device drivers should generally not use these routines directly. The PCI bus will enable decoding automatically when a SYS_RES_MEMORY or SYS_RES_IOPORT resource is activated via bus_alloc_resource(9) or bus_activate_resource(9).

The pci_get_max_payload() function returns the current maximum TLP payload size in bytes for a PCI-express device. If the dev device is not a PCI-express device, pci_get_max_payload() returns zero.

The pci_get_max_read_req() function returns the current maximum read request size in bytes for a PCI-express device. If the dev device is not a PCI-express device, pci_get_max_read_req() returns zero.

The pci_set_max_read_req() sets the PCI-express maximum read request size for dev. The requested size may be adjusted, and pci_set_max_read_req() returns the actual size set in bytes. If the dev device is not a PCI-express device, pci_set_max_read_req() returns zero.

The pci_get_powerstate() function returns the current power state of the device dev. If the device does not support power management capabilities, then the default state of PCI_POWERSTATE_D0 is returned. The following power states are defined by PCI:

PCI_POWERSTATE_D0

State in which device is on and running. It is receiving full power from the system and delivering full functionality to the user.

PCI_POWERSTATE_D1

Class-specific low-power state in which device context may or may not be lost. Busses in this state cannot do anything to the bus, to force devices to lose context.

PCI_POWERSTATE_D2

Class-specific low-power state in which device context may or may not be lost. Attains greater power savings than PCI_POWERSTATE_D1. Busses in this state can cause devices to lose some context. Devices must be prepared for the bus to be in this state or higher.

PCI_POWERSTATE_D3

State in which the device is off and not running. Device context is lost, and power from the device can be removed.

PCI_POWERSTATE_UNKNOWN

State of the device is unknown.

The pci_set_powerstate() function is used to transition the device dev to the PCI power state state. If the device does not support power management capabilities or it does not support the specific power state state, then the function will fail with EOPNOTSUPP.

The pci_iov_attach() function is used to advertise that the given device (and associated device driver) supports PCI Single-Root I/O Virtualization (SR-IOV). A driver that supports SR-IOV must implement the PCI_IOV_INIT(9), PCI_IOV_ADD_VF(9) and PCI_IOV_UNINIT(9) methods. This function should be called during the DEVICE_ATTACH(9) method. If this function returns an error, it is recommended that the device driver still successfully attaches, but runs with SR-IOV disabled. The pf_schema and vf_schema parameters are used to define what device-specific configuration parameters the device driver accepts when SR-IOV is enabled for the Physical Function (PF) and for individual Virtual Functions (VFs) respectively. See pci_iov_schema(9) for details on how to construct the schema. If either the pf_schema or vf_schema is invalid or specifies parameter names that conflict with parameter names that are already in use, pci_iov_attach() will return an error and SR-IOV will not be available on the PF device. If a driver does not accept configuration parameters for either the PF device or the VF devices, the driver must pass an empty schema for that device. The SR-IOV infrastructure takes ownership of the pf_schema and vf_schema and is responsible for freeing them. The driver must never free the schemas itself.

The pci_iov_detach() function is used to advise the SR-IOV infrastructure that the driver for the given device is attempting to detach and that all SR-IOV resources for the device must be released. This function must be called during the DEVICE_DETACH(9) method if pci_iov_attach() was successfully called on the device and pci_iov_detach() has not subsequently been called on the device and returned no error. If this function returns an error, the DEVICE_DETACH(9) method must fail and return an error, as detaching the PF driver while VF devices are active would cause system instability. This function is safe to call and will always succeed if pci_iov_attach() previously failed with an error on the given device, or if pci_iov_attach() was never called on the device.

The pci_save_state() and pci_restore_state() functions can be used by a device driver to save and restore standard PCI config registers. The pci_save_state() function must be invoked while the device has valid state before pci_restore_state() can be used. If the device is not in the fully-powered state (PCI_POWERSTATE_D0) when pci_restore_state() is invoked, then the device will be transitioned to PCI_POWERSTATE_D0 before any config registers are restored.

Message Signaled Interrupts¶

Message Signaled Interrupts (MSI) and Enhanced Message Signaled Interrupts (MSI-X) are PCI capabilities that provide an alternate method for PCI devices to signal interrupts. The legacy INTx interrupt is available to PCI devices as a SYS_RES_IRQ resource with a resource ID of zero. MSI and MSI-X interrupts are available to PCI devices as one or more SYS_RES_IRQ resources with resource IDs greater than zero. A driver must ask the PCI bus to allocate MSI or MSI-X interrupts using pci_alloc_msi() or pci_alloc_msix() before it can use MSI or MSI-X SYS_RES_IRQ resources. A driver is not allowed to use the legacy INTx SYS_RES_IRQ resource if MSI or MSI-X interrupts have been allocated, and attempts to allocate MSI or MSI-X interrupts will fail if the driver is currently using the legacy INTx SYS_RES_IRQ resource. A driver is only allowed to use either MSI or MSI-X, but not both.

The pci_msi_count() function returns the maximum number of MSI messages supported by the device dev. If the device does not support MSI, then pci_msi_count() returns zero.

The pci_alloc_msi() function attempts to allocate *count MSI messages for the device dev. The pci_alloc_msi() function may allocate fewer messages than requested for various reasons including requests for more messages than the device dev supports, or if the system has a shortage of available MSI messages. On success, *count is set to the number of messages allocated and pci_alloc_msi() returns zero. The SYS_RES_IRQ resources for the allocated messages will be available at consecutive resource IDs beginning with one. If pci_alloc_msi() is not able to allocate any messages, it returns an error. Note that MSI only supports message counts that are powers of two; requests to allocate a non-power of two count of messages will fail.

The pci_release_msi() function is used to release any allocated MSI or MSI-X messages back to the system. If any MSI or MSI-X SYS_RES_IRQ resources are allocated by the driver or have a configured interrupt handler, this function will fail with EBUSY. The pci_release_msi() function returns zero on success and an error on failure.

The pci_msix_count() function returns the maximum number of MSI-X messages supported by the device dev. If the device does not support MSI-X, then pci_msix_count() returns zero.

The pci_msix_pba_bar() function returns the offset in configuration space of the Base Address Register (BAR) containing the MSI-X Pending Bit Array (PBA) for device dev. The returned value can be used as the resource ID with bus_alloc_resource(9) and bus_release_resource(9) to allocate the BAR. If the device does not support MSI-X, then pci_msix_pba_bar() returns -1.

The pci_msix_table_bar() function returns the offset in configuration space of the BAR containing the MSI-X vector table for device dev. The returned value can be used as the resource ID with bus_alloc_resource(9) and bus_release_resource(9) to allocate the BAR. If the device does not support MSI-X, then pci_msix_table_bar() returns -1.

The pci_alloc_msix() function attempts to allocate *count MSI-X messages for the device dev. The pci_alloc_msix() function may allocate fewer messages than requested for various reasons including requests for more messages than the device dev supports, or if the system has a shortage of available MSI-X messages. On success, *count is set to the number of messages allocated and pci_alloc_msix() returns zero. For MSI-X messages, the resource ID for each SYS_RES_IRQ resource identifies the index in the MSI-X table of the corresponding message. A resource ID of one maps to the first index of the MSI-X table; a resource ID two identifies the second index in the table, etc. The pci_alloc_msix() function assigns the *count messages allocated to the first *count table indices. If pci_alloc_msix() is not able to allocate any messages, it returns an error. Unlike MSI, MSI-X does not require message counts that are powers of two.

The BARs containing the MSI-X vector table and PBA must be allocated via bus_alloc_resource(9) before calling pci_alloc_msix() and must not be released until after calling pci_release_msi(). Note that the vector table and PBA may be stored in the same BAR or in different BARs.

The pci_pending_msix() function examines the dev device's PBA to determine the pending status of the MSI-X message at table index index. If the indicated message is pending, this function returns a non-zero value; otherwise, it returns zero. Passing an invalid index to this function will result in undefined behavior.

As mentioned in the description of pci_alloc_msix(), MSI-X messages are initially assigned to the first N table entries. A driver may use a different distribution of available messages to table entries via the pci_remap_msix() function. Note that this function must be called after a successful call to pci_alloc_msix() but before any of the SYS_RES_IRQ resources are allocated. The pci_remap_msix() function returns zero on success, or an error on failure.

The vectors array should contain count message vectors. The array maps directly to the MSI-X table in that the first entry in the array specifies the message used for the first entry in the MSI-X table, the second entry in the array corresponds to the second entry in the MSI-X table, etc. The vector value in each array index can either be zero to indicate that no message should be assigned to the corresponding MSI-X table entry, or it can be a number from one to N (where N is the count returned from the previous call to pci_alloc_msix()) to indicate which of the allocated messages should be assigned to the corresponding MSI-X table entry.

If pci_remap_msix() succeeds, each MSI-X table entry with a non-zero vector will have an associated SYS_RES_IRQ resource whose resource ID corresponds to the table index as described above for pci_alloc_msix(). MSI-X table entries that with a vector of zero will not have an associated SYS_RES_IRQ resource. Additionally, if any of the original messages allocated by pci_alloc_msix() are not used in the new distribution of messages in the MSI-X table, they will be released automatically. Note that if a driver wishes to use fewer messages than were allocated by pci_alloc_msix(), the driver must use a single, contiguous range of messages beginning with one in the new distribution. The pci_remap_msix() function will fail if this condition is not met.