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