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PCI: Remove no longer correct documentation regarding MSI vector assignment

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The MSI vector reservation system described in Documentation/MSI-HOWTO.txt
was removed by Eric in 92db6d10bc. Remove
the references to it in the documentation.

While we're here § 5.5.1 refers to x86 hardware requirements, so make that
clear.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Michael Ellerman 2007-09-20 12:48:23 +10:00 committed by Greg Kroah-Hartman
parent 346ca04d05
commit 4904e23b6b
1 changed files with 4 additions and 65 deletions
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69
Documentation/MSI-HOWTO.txt
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@ -241,68 +241,7 @@ address space of the MSI-X table/MSI-X PBA. Otherwise, the PCI subsystem
will fail enabling MSI-X on its hardware device when it calls the function
pci_enable_msix().
5.3.2 Handling MSI-X allocation
Determining the number of MSI-X vectors allocated to a function is
dependent on the number of MSI capable devices and MSI-X capable
devices populated in the system. The policy of allocating MSI-X
vectors to a function is defined as the following:
#of MSI-X vectors allocated to a function = (x - y)/z where
x = The number of available PCI vector resources by the time
the device driver calls pci_enable_msix(). The PCI vector
resources is the sum of the number of unassigned vectors
(new) and the number of released vectors when any MSI/MSI-X
device driver switches its hardware device back to a legacy
mode or is hot-removed. The number of unassigned vectors
may exclude some vectors reserved, as defined in parameter
NR_HP_RESERVED_VECTORS, for the case where the system is
capable of supporting hot-add/hot-remove operations. Users
may change the value defined in NR_HR_RESERVED_VECTORS to
meet their specific needs.
y = The number of MSI capable devices populated in the system.
This policy ensures that each MSI capable device has its
vector reserved to avoid the case where some MSI-X capable
drivers may attempt to claim all available vector resources.
z = The number of MSI-X capable devices populated in the system.
This policy ensures that maximum (x - y) is distributed
evenly among MSI-X capable devices.
Note that the PCI subsystem scans y and z during a bus enumeration.
When the PCI subsystem completes configuring MSI/MSI-X capability
structure of a device as requested by its device driver, y/z is
decremented accordingly.
5.3.3 Handling MSI-X shortages
For the case where fewer MSI-X vectors are allocated to a function
than requested, the function pci_enable_msix() will return the
maximum number of MSI-X vectors available to the caller. A device
driver may re-send its request with fewer or equal vectors indicated
in the return. For example, if a device driver requests 5 vectors, but
the number of available vectors is 3 vectors, a value of 3 will be
returned as a result of pci_enable_msix() call. A function could be
designed for its driver to use only 3 MSI-X table entries as
different combinations as ABC--, A-B-C, A--CB, etc. Note that this
patch does not support multiple entries with the same vector. Such
attempt by a device driver to use 5 MSI-X table entries with 3 vectors
as ABBCC, AABCC, BCCBA, etc will result as a failure by the function
pci_enable_msix(). Below are the reasons why supporting multiple
entries with the same vector is an undesirable solution.
- The PCI subsystem cannot determine the entry that
generated the message to mask/unmask MSI while handling
software driver ISR. Attempting to walk through all MSI-X
table entries (2048 max) to mask/unmask any match vector
is an undesirable solution.
- Walking through all MSI-X table entries (2048 max) to handle
SMP affinity of any match vector is an undesirable solution.
5.3.4 API pci_enable_msix
5.3.2 API pci_enable_msix
int pci_enable_msix(struct pci_dev *dev, struct msix_entry *entries, int nvec)
@ -339,7 +278,7 @@ a failure. This failure may be a result of duplicate entries
specified in second argument, or a result of no available vector,
or a result of failing to initialize MSI-X table entries.
5.3.5 API pci_disable_msix
5.3.3 API pci_disable_msix
void pci_disable_msix(struct pci_dev *dev)
@ -349,7 +288,7 @@ always call free_irq() on all MSI-X vectors it has done request_irq()
on before calling this API. Failure to do so results in a BUG_ON() and
a device will be left with MSI-X enabled and leaks its vectors.
5.3.6 MSI-X mode vs. legacy mode diagram
5.3.4 MSI-X mode vs. legacy mode diagram
The below diagram shows the events which switch the interrupt
mode on the MSI-X capable device function between MSI-X mode and
@ -407,7 +346,7 @@ between MSI mod MSI-X mode during a run-time.
MSI/MSI-X support requires support from both system hardware and
individual hardware device functions.
5.5.1 System hardware support
5.5.1 Required x86 hardware support
Since the target of MSI address is the local APIC CPU, enabling
MSI/MSI-X support in the Linux kernel is dependent on whether existing