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PCI: Allow specifying devices using a base bus and path of devfns

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When specifying PCI devices on the kernel command line using a
bus/device/function address, bus numbers can change when adding or
replacing a device, changing motherboard firmware, or applying kernel
parameters like "pci=assign-buses".  When bus numbers change, it's likely
the command line tweak will be applied to the wrong device.

Therefore, it is useful to be able to specify devices with a base bus
number and the path of devfns needed to get to it, similar to the "device
scope" structure in the Intel VT-d spec, Section 8.3.1.

Thus, we add an option to specify devices in the following format:

  [<domain>:]<bus>:<device>.<func>[/<device>.<func>]*

The path can be any segment within the PCI hierarchy of any length and
determined through the use of 'lspci -t'.  When specified this way, it is
less likely that a renumbered bus will result in a valid device
specification and the tweak won't be applied to the wrong device.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
[bhelgaas: use "device" instead of "slot" in documentation since that's the
usual language in the PCI specs]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Stephen Bates <sbates@raithlin.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Christian König <christian.koenig@amd.com>
This commit is contained in:
Logan Gunthorpe
2018-07-30 10:18:38 -06:00
committed by Bjorn Helgaas
parent 07d8d7e57c
commit 45db33709c
2 changed files with 103 additions and 23 deletions
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8
Documentation/admin-guide/kernel-parameters.txt
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@@ -3000,7 +3000,7 @@
or a set of devices (<pci_dev>). These are
specified in one of the following formats:
[<domain>:]<bus>:<device>.<func>
[<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
pci:<vendor>:<device>[:<subvendor>:<subdevice>]
Note: the first format specifies a PCI
@@ -3009,7 +3009,11 @@
firmware changes, or due to changes caused
by other kernel parameters. If the
domain is left unspecified, it is
taken to be zero. The second format
taken to be zero. Optionally, a path
to a device through multiple device/function
addresses can be specified after the base
address (this is more robust against
renumbering issues). The second format
selects devices using IDs from the
configuration space which may match multiple
devices in the system.