diff options
Diffstat (limited to 'Documentation/pci.txt')
| -rw-r--r-- | Documentation/pci.txt | 37 |
1 files changed, 1 insertions, 36 deletions
diff --git a/Documentation/pci.txt b/Documentation/pci.txt index 7754f5aea4e..72b20c63959 100644 --- a/Documentation/pci.txt +++ b/Documentation/pci.txt @@ -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 |