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linux/Documentation/ABI/testing/sysfs-bus-pci
Alex Williamson 91fa127794 PCI: Expose PCIe Resizable BAR support via sysfs 
Add a simple sysfs interface to Resizable BAR support, largely for the
purposes of assigning such devices to a VM through VFIO.  Resizable BARs
present a difficult feature to expose to a VM through emulation, as
resizing a BAR is done on the host.  It can fail, and often does, but we
have no means via emulation of a PCIe REBAR capability to handle the error
cases.

A vfio-pci specific ioctl interface is also cumbersome as there are often
multiple devices within the same bridge aperture and handling them is a
challenge.  In the interface proposed here, expanding a BAR potentially
requires such devices to be soft-removed during the resize operation and
rescanned after, in order for all the necessary resources to be released.
A pci-sysfs interface is also more universal than a vfio specific
interface.

Please see the ABI documentation update for usage.

Link: https://lore.kernel.org/r/166336088796.3597940.14973499936692558556.stgit@omen
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: Krzysztof Wilczyński <kw@linux.com>
2022-10-05 12:21:02 -05:00

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What: /sys/bus/pci/drivers/.../bind
What: /sys/devices/pciX/.../bind
Date: December 2003
Contact: linux-pci@vger.kernel.org
Description:
Writing a device location to this file will cause
the driver to attempt to bind to the device found at
this location. This is useful for overriding default
bindings. The format for the location is: DDDD:BB:DD.F.
That is Domain:Bus:Device.Function and is the same as
found in /sys/bus/pci/devices/. For example::
# echo 0000:00:19.0 > /sys/bus/pci/drivers/foo/bind
(Note: kernels before 2.6.28 may require echo -n).
What: /sys/bus/pci/drivers/.../unbind
What: /sys/devices/pciX/.../unbind
Date: December 2003
Contact: linux-pci@vger.kernel.org
Description:
Writing a device location to this file will cause the
driver to attempt to unbind from the device found at
this location. This may be useful when overriding default
bindings. The format for the location is: DDDD:BB:DD.F.
That is Domain:Bus:Device.Function and is the same as
found in /sys/bus/pci/devices/. For example::
# echo 0000:00:19.0 > /sys/bus/pci/drivers/foo/unbind
(Note: kernels before 2.6.28 may require echo -n).
What: /sys/bus/pci/drivers/.../new_id
What: /sys/devices/pciX/.../new_id
Date: December 2003
Contact: linux-pci@vger.kernel.org
Description:
Writing a device ID to this file will attempt to
dynamically add a new device ID to a PCI device driver.
This may allow the driver to support more hardware than
was included in the driver's static device ID support
table at compile time. The format for the device ID is:
VVVV DDDD SVVV SDDD CCCC MMMM PPPP. That is Vendor ID,
Device ID, Subsystem Vendor ID, Subsystem Device ID,
Class, Class Mask, and Private Driver Data. The Vendor ID
and Device ID fields are required, the rest are optional.
Upon successfully adding an ID, the driver will probe
for the device and attempt to bind to it. For example::
# echo "8086 10f5" > /sys/bus/pci/drivers/foo/new_id
What: /sys/bus/pci/drivers/.../remove_id
What: /sys/devices/pciX/.../remove_id
Date: February 2009
Contact: Chris Wright <chrisw@sous-sol.org>
Description:
Writing a device ID to this file will remove an ID
that was dynamically added via the new_id sysfs entry.
The format for the device ID is:
VVVV DDDD SVVV SDDD CCCC MMMM. That is Vendor ID, Device
ID, Subsystem Vendor ID, Subsystem Device ID, Class,
and Class Mask. The Vendor ID and Device ID fields are
required, the rest are optional. After successfully
removing an ID, the driver will no longer support the
device. This is useful to ensure auto probing won't
match the driver to the device. For example::
# echo "8086 10f5" > /sys/bus/pci/drivers/foo/remove_id
What: /sys/bus/pci/rescan
Date: January 2009
Contact: Linux PCI developers <linux-pci@vger.kernel.org>
Description:
Writing a non-zero value to this attribute will
force a rescan of all PCI buses in the system, and
re-discover previously removed devices.
What: /sys/bus/pci/devices/.../msi_bus
Date: September 2014
Contact: Linux PCI developers <linux-pci@vger.kernel.org>
Description:
Writing a zero value to this attribute disallows MSI and
MSI-X for any future drivers of the device. If the device
is a bridge, MSI and MSI-X will be disallowed for future
drivers of all child devices under the bridge. Drivers
must be reloaded for the new setting to take effect.
What: /sys/bus/pci/devices/.../msi_irqs/
Date: September, 2011
Contact: Neil Horman <nhorman@tuxdriver.com>
Description:
The /sys/devices/.../msi_irqs directory contains a variable set
of files, with each file being named after a corresponding msi
irq vector allocated to that device.
What: /sys/bus/pci/devices/.../msi_irqs/<N>
Date: September 2011
Contact: Neil Horman <nhorman@tuxdriver.com>
Description:
This attribute indicates the mode that the irq vector named by
the file is in (msi vs. msix)
What: /sys/bus/pci/devices/.../irq
Date: August 2021
Contact: Linux PCI developers <linux-pci@vger.kernel.org>
Description:
If a driver has enabled MSI (not MSI-X), "irq" contains the
IRQ of the first MSI vector. Otherwise "irq" contains the
IRQ of the legacy INTx interrupt.
"irq" being set to 0 indicates that the device isn't
capable of generating legacy INTx interrupts.
What: /sys/bus/pci/devices/.../remove
Date: January 2009
Contact: Linux PCI developers <linux-pci@vger.kernel.org>
Description:
Writing a non-zero value to this attribute will
hot-remove the PCI device and any of its children.
What: /sys/bus/pci/devices/.../pci_bus/.../rescan
Date: May 2011
Contact: Linux PCI developers <linux-pci@vger.kernel.org>
Description:
Writing a non-zero value to this attribute will
force a rescan of the bus and all child buses,
and re-discover devices removed earlier from this
part of the device tree.
What: /sys/bus/pci/devices/.../rescan
Date: January 2009
Contact: Linux PCI developers <linux-pci@vger.kernel.org>
Description:
Writing a non-zero value to this attribute will
force a rescan of the device's parent bus and all
child buses, and re-discover devices removed earlier
from this part of the device tree.
What: /sys/bus/pci/devices/.../reset_method
Date: August 2021
Contact: Amey Narkhede <ameynarkhede03@gmail.com>
Description:
Some devices allow an individual function to be reset
without affecting other functions in the same slot.
For devices that have this support, a file named
reset_method is present in sysfs. Reading this file
gives names of the supported and enabled reset methods and
their ordering. Writing a space-separated list of names of
reset methods sets the reset methods and ordering to be
used when resetting the device. Writing an empty string
disables the ability to reset the device. Writing
"default" enables all supported reset methods in the
default ordering.
What: /sys/bus/pci/devices/.../reset
Date: July 2009
Contact: Michael S. Tsirkin <mst@redhat.com>
Description:
Some devices allow an individual function to be reset
without affecting other functions in the same device.
For devices that have this support, a file named reset
will be present in sysfs. Writing 1 to this file
will perform reset.
What: /sys/bus/pci/devices/.../vpd
Date: February 2008
Contact: Ben Hutchings <bwh@kernel.org>
Description:
A file named vpd in a device directory will be a
binary file containing the Vital Product Data for the
device. It should follow the VPD format defined in
PCI Specification 2.1 or 2.2, but users should consider
that some devices may have incorrectly formatted data.
If the underlying VPD has a writable section then the
corresponding section of this file will be writable.
What: /sys/bus/pci/devices/.../virtfn<N>
Date: March 2009
Contact: Yu Zhao <yu.zhao@intel.com>
Description:
This symbolic link appears when hardware supports the SR-IOV
capability and the Physical Function driver has enabled it.
The symbolic link points to the PCI device sysfs entry of the
Virtual Function whose index is N (0...MaxVFs-1).
What: /sys/bus/pci/devices/.../dep_link
Date: March 2009
Contact: Yu Zhao <yu.zhao@intel.com>
Description:
This symbolic link appears when hardware supports the SR-IOV
capability and the Physical Function driver has enabled it,
and this device has vendor specific dependencies with others.
The symbolic link points to the PCI device sysfs entry of
Physical Function this device depends on.
What: /sys/bus/pci/devices/.../physfn
Date: March 2009
Contact: Yu Zhao <yu.zhao@intel.com>
Description:
This symbolic link appears when a device is a Virtual Function.
The symbolic link points to the PCI device sysfs entry of the
Physical Function this device associates with.
What: /sys/bus/pci/devices/.../modalias
Date: May 2005
Contact: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Description:
This attribute indicates the PCI ID of the device object.
That is in the format:
pci:vXXXXXXXXdXXXXXXXXsvXXXXXXXXsdXXXXXXXXbcXXscXXiXX,
where:
- vXXXXXXXX contains the vendor ID;
- dXXXXXXXX contains the device ID;
- svXXXXXXXX contains the sub-vendor ID;
- sdXXXXXXXX contains the subsystem device ID;
- bcXX contains the device class;
- scXX contains the device subclass;
- iXX contains the device class programming interface.
What: /sys/bus/pci/slots/.../module
Date: June 2009
Contact: linux-pci@vger.kernel.org
Description:
This symbolic link points to the PCI hotplug controller driver
module that manages the hotplug slot.
What: /sys/bus/pci/devices/.../label
Date: July 2010
Contact: Narendra K <narendra_k@dell.com>, linux-bugs@dell.com
Description:
Reading this attribute will provide the firmware
given name (SMBIOS type 41 string or ACPI _DSM string) of
the PCI device. The attribute will be created only
if the firmware has given a name to the PCI device.
ACPI _DSM string name will be given priority if the
system firmware provides SMBIOS type 41 string also.
Users:
Userspace applications interested in knowing the
firmware assigned name of the PCI device.
What: /sys/bus/pci/devices/.../index
Date: July 2010
Contact: Narendra K <narendra_k@dell.com>, linux-bugs@dell.com
Description:
Reading this attribute will provide the firmware given instance
number of the PCI device. Depending on the platform this can
be for example the SMBIOS type 41 device type instance or the
user-defined ID (UID) on s390. The attribute will be created
only if the firmware has given an instance number to the PCI
device and that number is guaranteed to uniquely identify the
device in the system.
Users:
Userspace applications interested in knowing the
firmware assigned device type instance of the PCI
device that can help in understanding the firmware
intended order of the PCI device.
What: /sys/bus/pci/devices/.../acpi_index
Date: July 2010
Contact: Narendra K <narendra_k@dell.com>, linux-bugs@dell.com
Description:
Reading this attribute will provide the firmware
given instance (ACPI _DSM instance number) of the PCI device.
The attribute will be created only if the firmware has given
an instance number to the PCI device. ACPI _DSM instance number
will be given priority if the system firmware provides SMBIOS
type 41 device type instance also.
Users:
Userspace applications interested in knowing the
firmware assigned instance number of the PCI
device that can help in understanding the firmware
intended order of the PCI device.
What: /sys/bus/pci/devices/.../d3cold_allowed
Date: July 2012
Contact: Huang Ying <ying.huang@intel.com>
Description:
d3cold_allowed is bit to control whether the corresponding PCI
device can be put into D3Cold state. If it is cleared, the
device will never be put into D3Cold state. If it is set, the
device may be put into D3Cold state if other requirements are
satisfied too. Reading this attribute will show the current
value of d3cold_allowed bit. Writing this attribute will set
the value of d3cold_allowed bit.
What: /sys/bus/pci/devices/.../sriov_totalvfs
Date: November 2012
Contact: Donald Dutile <ddutile@redhat.com>
Description:
This file appears when a physical PCIe device supports SR-IOV.
Userspace applications can read this file to determine the
maximum number of Virtual Functions (VFs) a PCIe physical
function (PF) can support. Typically, this is the value reported
in the PF's SR-IOV extended capability structure's TotalVFs
element. Drivers have the ability at probe time to reduce the
value read from this file via the pci_sriov_set_totalvfs()
function.
What: /sys/bus/pci/devices/.../sriov_numvfs
Date: November 2012
Contact: Donald Dutile <ddutile@redhat.com>
Description:
This file appears when a physical PCIe device supports SR-IOV.
Userspace applications can read and write to this file to
determine and control the enablement or disablement of Virtual
Functions (VFs) on the physical function (PF). A read of this
file will return the number of VFs that are enabled on this PF.
A number written to this file will enable the specified
number of VFs. A userspace application would typically read the
file and check that the value is zero, and then write the number
of VFs that should be enabled on the PF; the value written
should be less than or equal to the value in the sriov_totalvfs
file. A userspace application wanting to disable the VFs would
write a zero to this file. The core ensures that valid values
are written to this file, and returns errors when values are not
valid. For example, writing a 2 to this file when sriov_numvfs
is not 0 and not 2 already will return an error. Writing a 10
when the value of sriov_totalvfs is 8 will return an error.
What: /sys/bus/pci/devices/.../driver_override
Date: April 2014
Contact: Alex Williamson <alex.williamson@redhat.com>
Description:
This file allows the driver for a device to be specified which
will override standard static and dynamic ID matching. When
specified, only a driver with a name matching the value written
to driver_override will have an opportunity to bind to the
device. The override is specified by writing a string to the
driver_override file (echo pci-stub > driver_override) and
may be cleared with an empty string (echo > driver_override).
This returns the device to standard matching rules binding.
Writing to driver_override does not automatically unbind the
device from its current driver or make any attempt to
automatically load the specified driver. If no driver with a
matching name is currently loaded in the kernel, the device
will not bind to any driver. This also allows devices to
opt-out of driver binding using a driver_override name such as
"none". Only a single driver may be specified in the override,
there is no support for parsing delimiters.
What: /sys/bus/pci/devices/.../numa_node
Date: Oct 2014
Contact: Prarit Bhargava <prarit@redhat.com>
Description:
This file contains the NUMA node to which the PCI device is
attached, or -1 if the node is unknown. The initial value
comes from an ACPI _PXM method or a similar firmware
source. If that is missing or incorrect, this file can be
written to override the node. In that case, please report
a firmware bug to the system vendor. Writing to this file
taints the kernel with TAINT_FIRMWARE_WORKAROUND, which
reduces the supportability of your system.
What: /sys/bus/pci/devices/.../revision
Date: November 2016
Contact: Emil Velikov <emil.l.velikov@gmail.com>
Description:
This file contains the revision field of the PCI device.
The value comes from device config space. The file is read only.
What: /sys/bus/pci/devices/.../sriov_drivers_autoprobe
Date: April 2017
Contact: Bodong Wang<bodong@mellanox.com>
Description:
This file is associated with the PF of a device that
supports SR-IOV. It determines whether newly-enabled VFs
are immediately bound to a driver. It initially contains
1, which means the kernel automatically binds VFs to a
compatible driver immediately after they are enabled. If
an application writes 0 to the file before enabling VFs,
the kernel will not bind VFs to a driver.
A typical use case is to write 0 to this file, then enable
VFs, then assign the newly-created VFs to virtual machines.
Note that changing this file does not affect already-
enabled VFs. In this scenario, the user must first disable
the VFs, write 0 to sriov_drivers_autoprobe, then re-enable
the VFs.
This is similar to /sys/bus/pci/drivers_autoprobe, but
affects only the VFs associated with a specific PF.
What: /sys/bus/pci/devices/.../p2pmem/size
Date: November 2017
Contact: Logan Gunthorpe <logang@deltatee.com>
Description:
If the device has any Peer-to-Peer memory registered, this
file contains the total amount of memory that the device
provides (in decimal).
What: /sys/bus/pci/devices/.../p2pmem/available
Date: November 2017
Contact: Logan Gunthorpe <logang@deltatee.com>
Description:
If the device has any Peer-to-Peer memory registered, this
file contains the amount of memory that has not been
allocated (in decimal).
What: /sys/bus/pci/devices/.../p2pmem/published
Date: November 2017
Contact: Logan Gunthorpe <logang@deltatee.com>
Description:
If the device has any Peer-to-Peer memory registered, this
file contains a '1' if the memory has been published for
use outside the driver that owns the device.
What: /sys/bus/pci/devices/.../link/clkpm
/sys/bus/pci/devices/.../link/l0s_aspm
/sys/bus/pci/devices/.../link/l1_aspm
/sys/bus/pci/devices/.../link/l1_1_aspm
/sys/bus/pci/devices/.../link/l1_2_aspm
/sys/bus/pci/devices/.../link/l1_1_pcipm
/sys/bus/pci/devices/.../link/l1_2_pcipm
Date: October 2019
Contact: Heiner Kallweit <hkallweit1@gmail.com>
Description: If ASPM is supported for an endpoint, these files can be
used to disable or enable the individual power management
states. Write y/1/on to enable, n/0/off to disable.
What: /sys/bus/pci/devices/.../power_state
Date: November 2020
Contact: Linux PCI developers <linux-pci@vger.kernel.org>
Description:
This file contains the current PCI power state of the device.
The value comes from the PCI kernel device state and can be one
of: "unknown", "error", "D0", D1", "D2", "D3hot", "D3cold".
The file is read only.
What: /sys/bus/pci/devices/.../sriov_vf_total_msix
Date: January 2021
Contact: Leon Romanovsky <leonro@nvidia.com>
Description:
This file is associated with a SR-IOV physical function (PF).
It contains the total number of MSI-X vectors available for
assignment to all virtual functions (VFs) associated with PF.
The value will be zero if the device doesn't support this
functionality. For supported devices, the value will be
constant and won't be changed after MSI-X vectors assignment.
What: /sys/bus/pci/devices/.../sriov_vf_msix_count
Date: January 2021
Contact: Leon Romanovsky <leonro@nvidia.com>
Description:
This file is associated with a SR-IOV virtual function (VF).
It allows configuration of the number of MSI-X vectors for
the VF. This allows devices that have a global pool of MSI-X
vectors to optimally divide them between VFs based on VF usage.
The values accepted are:
* > 0 - this number will be reported as the Table Size in the
VF's MSI-X capability
* < 0 - not valid
* = 0 - will reset to the device default value
The file is writable if the PF is bound to a driver that
implements ->sriov_set_msix_vec_count().
What: /sys/bus/pci/devices/.../resourceN_resize
Date: September 2022
Contact: Alex Williamson <alex.williamson@redhat.com>
Description:
These files provide an interface to PCIe Resizable BAR support.
A file is created for each BAR resource (N) supported by the
PCIe Resizable BAR extended capability of the device. Reading
each file exposes the bitmap of available resource sizes:
# cat resource1_resize
00000000000001c0
The bitmap represents supported resource sizes for the BAR,
where bit0 = 1MB, bit1 = 2MB, bit2 = 4MB, etc. In the above
example the device supports 64MB, 128MB, and 256MB BAR sizes.
When writing the file, the user provides the bit position of
the desired resource size, for example:
# echo 7 > resource1_resize
This indicates to set the size value corresponding to bit 7,
128MB. The resulting size is 2 ^ (bit# + 20). This definition
matches the PCIe specification of this capability.
In order to make use of resource resizing, all PCI drivers must
be unbound from the device and peer devices under the same
parent bridge may need to be soft removed. In the case of
VGA devices, writing a resize value will remove low level
console drivers from the device. Raw users of pci-sysfs
resourceN attributes must be terminated prior to resizing.
Success of the resizing operation is not guaranteed.
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