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PCI: Add arch_can_pci_mmap_wc() macro

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Most of the almost-identical versions of pci_mmap_page_range() silently
ignore the 'write_combine' argument and give uncached mappings.

Yet we allow the PCIIOC_WRITE_COMBINE ioctl in /proc/bus/pci, expose the
'resourceX_wc' file in sysfs, and allow an attempted mapping to apparently
succeed.

To fix this, introduce a macro arch_can_pci_mmap_wc() which indicates
whether the platform can do a write-combining mapping.  On x86 this ends up
being pat_enabled(), while the few other platforms that support it can just
set it to a literal '1'.

Signed-off-by: David Woodhouse <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
This commit is contained in:
David Woodhouse 2017-04-12 13:25:54 +01:00 • committed by Bjorn Helgaas
commit ae749c7ab4
7 changed files with 25 additions and 11 deletions
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4
Documentation/filesystems/sysfs-pci.txt
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@ -117,6 +117,10 @@ code must define HAVE_PCI_MMAP and provide a pci_mmap_page_range function.
Platforms are free to only support subsets of the mmap functionality, but
useful return codes should be provided.
Platforms which support write-combining maps of PCI resources must define
arch_can_pci_mmap_wc() which shall evaluate to non-zero at runtime when
write-combining is permitted.
Legacy resources are protected by the HAVE_PCI_LEGACY define. Platforms
wishing to support legacy functionality should define it and provide
pci_legacy_read, pci_legacy_write and pci_mmap_legacy_page_range functions.