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, ...)
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@xxxxxxxxxx>
---
drivers/pci/proc.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
index 3f155e7..2408abe 100644
--- a/drivers/pci/proc.c
+++ b/drivers/pci/proc.c
@@ -231,7 +231,7 @@ static int proc_bus_pci_mmap(struct file *file, struct vm_area_struct *vma)
{
struct pci_dev *dev = PDE_DATA(file_inode(file));
struct pci_filp_private *fpriv = file->private_data;
- int i, ret;
+ int i, ret, write_combine;
if (!capable(CAP_SYS_RAWIO))
return -EPERM;
@@ -245,9 +245,12 @@ static int proc_bus_pci_mmap(struct file *file, struct vm_area_struct *vma)
if (i >= PCI_ROM_RESOURCE)
return -ENODEV;
+ if (fpriv->mmap_state == pci_mmap_mem)
+ write_combine = fpriv->write_combine;
+ else
+ write_combine = 0;
ret = pci_mmap_page_range(dev, vma,
- fpriv->mmap_state,
- fpriv->write_combine);
+ fpriv->mmap_state, write_combine);
if (ret < 0)
return ret;
--
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