PCI: Ignore write combining when mapping I/O port space
PCI exposes files like /proc/bus/pci/00/00.0 in procfs. These files
support operations like this:
ioctl(fd, PCIIOC_MMAP_IS_IO); # request I/O port space
ioctl(fd, PCIIOC_WRITE_COMBINE, 1); # request write-combining
mmap(fd, ...)
Write combining is useful on PCI memory space, but I don't think it makes
sense on PCI I/O port space.
We *could* change proc_bus_pci_ioctl() to make it impossible to set
mmap_state == pci_mmap_io and write_combine at the same time, but that
would break the following sequence, which is currently legal:
mmap(fd, ...) # default is I/O, non-combining
ioctl(fd, PCIIOC_WRITE_COMBINE, 1); # request write-combining
ioctl(fd, PCIIOC_MMAP_IS_MEM); # request memory space
mmap(fd, ...) # get write-combining mapping
Ignore the write-combining flag when mapping I/O port space.
This patch should have no functional effect, based on this analysis of all
implementations of pci_mmap_page_range():
- ia64 mips parisc sh unicore32 x86 do not support mapping of I/O port
space at all.
- arm cris microblaze mn10300 sparc xtensa support mapping of I/O port
space, but ignore the write_combine argument to pci_mmap_page_range().
- powerpc supports mapping of I/O port space and uses write_combine, and
it disables write combining for I/O port space in
__pci_mmap_set_pgprot().
This patch makes it possible to remove __pci_mmap_set_pgprot() from
powerpc, which simplifies that path.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
1 file changed