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PCI: Remove pci_enable_device_bars() from documentation

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Patch below removes pci_enable_device_bars() from Documentation/pci.txt .

Signed-off-by: Grant Grundler <grundler@parisc-linux.org>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Grant Grundler 2007-12-24 00:08:51 -07:00 committed by Greg Kroah-Hartman
parent 7cbe5b6005
commit d48b5d3a50
1 changed files with 1 additions and 36 deletions
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37
Documentation/pci.txt
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@ -274,8 +274,6 @@ the PCI device by calling pci_enable_device(). This will:
o allocate an IRQ (if BIOS did not).
NOTE: pci_enable_device() can fail! Check the return value.
NOTE2: Also see pci_enable_device_bars() below. Drivers can
attempt to enable only a subset of BARs they need.
[ OS BUG: we don't check resource allocations before enabling those
resources. The sequence would make more sense if we called
@ -605,40 +603,7 @@ device lists. This is still possible but discouraged.
10. pci_enable_device_bars() and Legacy I/O Port space
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Large servers may not be able to provide I/O port resources to all PCI
devices. I/O Port space is only 64KB on Intel Architecture[1] and is
likely also fragmented since the I/O base register of PCI-to-PCI
bridge will usually be aligned to a 4KB boundary[2]. On such systems,
pci_enable_device() and pci_request_region() will fail when
attempting to enable I/O Port regions that don't have I/O Port
resources assigned.
Fortunately, many PCI devices which request I/O Port resources also
provide access to the same registers via MMIO BARs. These devices can
be handled without using I/O port space and the drivers typically
offer a CONFIG_ option to only use MMIO regions
(e.g. CONFIG_TULIP_MMIO). PCI devices typically provide I/O port
interface for legacy OSes and will work when I/O port resources are not
assigned. The "PCI Local Bus Specification Revision 3.0" discusses
this on p.44, "IMPLEMENTATION NOTE".
If your PCI device driver doesn't need I/O port resources assigned to
I/O Port BARs, you should use pci_enable_device_bars() instead of
pci_enable_device() in order not to enable I/O port regions for the
corresponding devices. In addition, you should use
pci_request_selected_regions() and pci_release_selected_regions()
instead of pci_request_regions()/pci_release_regions() in order not to
request/release I/O port regions for the corresponding devices.
[1] Some systems support 64KB I/O port space per PCI segment.
[2] Some PCI-to-PCI bridges support optional 1KB aligned I/O base.
11. MMIO Space and "Write Posting"
10. MMIO Space and "Write Posting"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Converting a driver from using I/O Port space to using MMIO space