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Commit d48b5d3a authored by Grant Grundler's avatar Grant Grundler Committed by Greg Kroah-Hartman
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PCI: Remove pci_enable_device_bars() from documentation 



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

Signed-off-by: default avatarGrant Grundler <grundler@parisc-linux.org>
Acked-by: default avatarAlan Cox <alan@redhat.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 7cbe5b60

Documentation/pci.txt

+1 −36
Original line number Diff line number Diff line
@@ -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