On Thu, Jun 09, 2016 at 01:20:23PM -0500, Bjorn Helgaas wrote:
> From: Yinghai Lu <yinghai@xxxxxxxxxx>
>
> The powerpc-specific __pci_mmap_set_pgprot() does two things:
>
> 1) Disables write combining for I/O port space mappings
>
> This only affects procfs mappings. The pci_mmap_resource() sysfs path
> only requests write combining for resources with IORESOURCE_PREFETCH
> set, which doesn't include I/O resources.
>
> The only way to request write combining for I/O port space mappings
> was via the PCIIOC_WRITE_COMBINE ioctl and the proc_bus_pci_mmap()
> path, and we recently changed that path to ignore write combining for
> I/O, so this code in powerpc is no longer needed.
>
> 2) Automatically enables write combining for mappings of prefetchable
> resources, even if not requested by the user
>
> Both procfs (via PCIIOC_MMAP_IS_MEM and PCIIOC_WRITE_COMBINE ioctls)
> and sysfs (via "resourceN_wc" files, which are created for resources
> with IORESOURCE_PREFETCH) provide ways for the user to map PCI memory
> space with write combining.
>
> Users that desire write combining should use one of those ways instead
> of relying on powerpc-specific behavior.
>
> Remove the powerpc-specific __pci_mmap_set_pgprot().
>
> The user-visible effect of this change is that users mapping prefetchable
> PCI memory space via procfs without PCIIOC_WRITE_COMBINE or via sysfs
> "resourceN" (not "resourceN_wc") will get regular uncacheable mappings
> instead of the write combining mappings they used to get.
>
> The new behavior matches the behavior on all other arches that support
> write combining mapping.
Powerpc folks, any thoughts on this?
It's currently on my pci/resource branch, and I plan to merge it for
v4.8 if there are no objections.
> [bhelgaas: changelog]
> Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>
> Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> ---
> arch/powerpc/kernel/pci-common.c | 37 ++++---------------------------------
> 1 file changed, 4 insertions(+), 33 deletions(-)
>
> diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
> index 0f7a60f..8c6beb0 100644
> --- a/arch/powerpc/kernel/pci-common.c
> +++ b/arch/powerpc/kernel/pci-common.c
> @@ -356,36 +356,6 @@ static struct resource *__pci_mmap_make_offset(struct pci_dev *dev,
> }
>
> /*
> - * Set vm_page_prot of VMA, as appropriate for this architecture, for a pci
> - * device mapping.
> - */
> -static pgprot_t __pci_mmap_set_pgprot(struct pci_dev *dev, struct resource *rp,
> - pgprot_t protection,
> - enum pci_mmap_state mmap_state,
> - int write_combine)
> -{
> -
> - /* Write combine is always 0 on non-memory space mappings. On
> - * memory space, if the user didn't pass 1, we check for a
> - * "prefetchable" resource. This is a bit hackish, but we use
> - * this to workaround the inability of /sysfs to provide a write
> - * combine bit
> - */
> - if (mmap_state != pci_mmap_mem)
> - write_combine = 0;
> - else if (write_combine == 0) {
> - if (rp->flags & IORESOURCE_PREFETCH)
> - write_combine = 1;
> - }
> -
> - /* XXX would be nice to have a way to ask for write-through */
> - if (write_combine)
> - return pgprot_noncached_wc(protection);
> - else
> - return pgprot_noncached(protection);
> -}
> -
> -/*
> * This one is used by /dev/mem and fbdev who have no clue about the
> * PCI device, it tries to find the PCI device first and calls the
> * above routine
> @@ -458,9 +428,10 @@ int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
> return -EINVAL;
>
> vma->vm_pgoff = offset >> PAGE_SHIFT;
> - vma->vm_page_prot = __pci_mmap_set_pgprot(dev, rp,
> - vma->vm_page_prot,
> - mmap_state, write_combine);
> + if (write_combine)
> + vma->vm_page_prot = pgprot_noncached_wc(vma->vm_page_prot);
> + else
> + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>
> ret = remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
> vma->vm_end - vma->vm_start, vma->vm_page_prot);
>
> --
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