Re: [PATCH 04/17] pci: Add arch_can_pci_mmap_wc() macro

[David Woodhouse]

On Tue, 2017-04-04 at 16:36 -0500, Bjorn Helgaas wrote:
> > --- a/arch/xtensa/kernel/pci.c
> > +++ b/arch/xtensa/kernel/pci.c
> > @@ -345,7 +345,7 @@ __pci_mmap_set_pgprot(struct pci_dev *dev, struct 
> > vm_area_struct *vma,
> >  
> >     /* Set to write-through */
> >     prot = (prot & _PAGE_CA_MASK) | _PAGE_CA_WT;
> > -#if 0
> > +#ifdef arch_can_pci_mmap_wc
>
> This hunk seems like maybe it should be a separate patch.
> 
> ...
>
> This part seems different -- it changes the way pci_mmap_page_range()
> works.

It doesn't, because arch_can_pci_map_wc isn't defined on xtensa. So
it's just a trivial cleanup for future-proofing, turning that 'if 0'
into 'if '.

> > diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
> > index dc8912e..c49be71 100644
> > --- a/drivers/pci/proc.c
> > +++ b/drivers/pci/proc.c
> > @@ -209,15 +209,18 @@ static long proc_bus_pci_ioctl(struct file *file, 
> > unsigned int cmd,
> >     fpriv->mmap_state = pci_mmap_mem;
> >     break;
> >  
> > +#ifdef arch_can_pci_mmap_wc
> Can we get rid of these #ifdefs in the code by adding this to linux/pci.h?
> 
>   #ifndef arch_can_pci_mmap_wc
>   #define arch_can_pci_mmap_wc()  0
>   #endif

Er at the time, that was non-trivial because there was something
that actually needed to be *removed* with the preprocessor instead of
just not being called. But after I settled on the incremental approach
of having pci_mmap_resource_range() be a wrapper for
pci_mmap_page_range() *and* vice versa I think that requirement went
away. I'll take another look and see if I can do that now; thanks.

Are you happy with the suggestion that we use HAVE_PCI_MMAP *only* to
control mmap on /proc/bus/pci, and we present mmap through sysfs on all
platforms via the generic code?

smime.p7s
Description: S/MIME cryptographic signature

Re: [PATCH 04/17] pci: Add arch_can_pci_mmap_wc() macro

[David Woodhouse]

On Tue, 2017-04-04 at 16:36 -0500, Bjorn Helgaas wrote:
> > --- a/arch/xtensa/kernel/pci.c
> > +++ b/arch/xtensa/kernel/pci.c
> > @@ -345,7 +345,7 @@ __pci_mmap_set_pgprot(struct pci_dev *dev, struct 
> > vm_area_struct *vma,
> >  
> >     /* Set to write-through */
> >     prot = (prot & _PAGE_CA_MASK) | _PAGE_CA_WT;
> > -#if 0
> > +#ifdef arch_can_pci_mmap_wc
>
> This hunk seems like maybe it should be a separate patch.
> 
> ...
>
> This part seems different -- it changes the way pci_mmap_page_range()
> works.

It doesn't, because arch_can_pci_map_wc isn't defined on xtensa. So
it's just a trivial cleanup for future-proofing, turning that 'if 0'
into 'if '.

> > diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
> > index dc8912e..c49be71 100644
> > --- a/drivers/pci/proc.c
> > +++ b/drivers/pci/proc.c
> > @@ -209,15 +209,18 @@ static long proc_bus_pci_ioctl(struct file *file, 
> > unsigned int cmd,
> >     fpriv->mmap_state = pci_mmap_mem;
> >     break;
> >  
> > +#ifdef arch_can_pci_mmap_wc
> Can we get rid of these #ifdefs in the code by adding this to linux/pci.h?
> 
>   #ifndef arch_can_pci_mmap_wc
>   #define arch_can_pci_mmap_wc()  0
>   #endif

Er at the time, that was non-trivial because there was something
that actually needed to be *removed* with the preprocessor instead of
just not being called. But after I settled on the incremental approach
of having pci_mmap_resource_range() be a wrapper for
pci_mmap_page_range() *and* vice versa I think that requirement went
away. I'll take another look and see if I can do that now; thanks.

Are you happy with the suggestion that we use HAVE_PCI_MMAP *only* to
control mmap on /proc/bus/pci, and we present mmap through sysfs on all
platforms via the generic code?

smime.p7s
Description: S/MIME cryptographic signature

Re: [PATCH 04/17] pci: Add arch_can_pci_mmap_wc() macro

[Bjorn Helgaas]

On Wed, Mar 22, 2017 at 01:25:18PM +, David Woodhouse wrote:
> From: David Woodhouse 
> 
> 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 
> ---
>  Documentation/filesystems/sysfs-pci.txt |  4 
>  arch/ia64/include/asm/pci.h |  2 ++
>  arch/powerpc/include/asm/pci.h  |  5 +++--
>  arch/x86/include/asm/pci.h  |  2 ++
>  arch/xtensa/include/asm/pci.h   |  6 +-
>  arch/xtensa/kernel/pci.c|  2 +-
>  drivers/pci/pci-sysfs.c |  6 --
>  drivers/pci/proc.c  | 17 ++---
>  8 files changed, 31 insertions(+), 13 deletions(-)
> 
> diff --git a/Documentation/filesystems/sysfs-pci.txt 
> b/Documentation/filesystems/sysfs-pci.txt
> index 6ea1ced..25b7f1c 100644
> --- a/Documentation/filesystems/sysfs-pci.txt
> +++ b/Documentation/filesystems/sysfs-pci.txt
> @@ -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.
> diff --git a/arch/ia64/include/asm/pci.h b/arch/ia64/include/asm/pci.h
> index c0835b0..6283758 100644
> --- a/arch/ia64/include/asm/pci.h
> +++ b/arch/ia64/include/asm/pci.h
> @@ -51,6 +51,8 @@ extern unsigned long ia64_max_iommu_merge_mask;
>  #define PCI_DMA_BUS_IS_PHYS  (ia64_max_iommu_merge_mask == ~0UL)
>  
>  #define HAVE_PCI_MMAP
> +#define arch_can_pci_mmap_wc()   1
> +
>  extern int pci_mmap_page_range (struct pci_dev *dev, struct vm_area_struct 
> *vma,
>   enum pci_mmap_state mmap_state, int 
> write_combine);
>  #define HAVE_PCI_LEGACY
> diff --git a/arch/powerpc/include/asm/pci.h b/arch/powerpc/include/asm/pci.h
> index 93eded8..b5b68c6 100644
> --- a/arch/powerpc/include/asm/pci.h
> +++ b/arch/powerpc/include/asm/pci.h
> @@ -81,8 +81,9 @@ struct vm_area_struct;
>  int pci_mmap_page_range(struct pci_dev *pdev, struct vm_area_struct *vma,
>   enum pci_mmap_state mmap_state, int write_combine);
>  
> -/* Tell drivers/pci/proc.c that we have pci_mmap_page_range() */
> -#define HAVE_PCI_MMAP1
> +/* Tell drivers/pci/proc.c that we have pci_mmap_page_range() and it does WC 
> */
> +#define HAVE_PCI_MMAP1
> +#define arch_can_pci_mmap_wc()   1
>  
>  extern int pci_legacy_read(struct pci_bus *bus, loff_t port, u32 *val,
>  size_t count);
> diff --git a/arch/x86/include/asm/pci.h b/arch/x86/include/asm/pci.h
> index 1411dbe..f6e22c2 100644
> --- a/arch/x86/include/asm/pci.h
> +++ b/arch/x86/include/asm/pci.h
> @@ -7,6 +7,7 @@
>  #include 
>  #include 
>  #include 
> +#include 
>  #include 
>  
>  #ifdef __KERNEL__
> @@ -102,6 +103,7 @@ int pcibios_set_irq_routing(struct pci_dev *dev, int pin, 
> int irq);
>  
>  
>  #define HAVE_PCI_MMAP
> +#define arch_can_pci_mmap_wc()   pat_enabled()
>  extern int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct 
> *vma,
>  enum pci_mmap_state mmap_state,
>  int write_combine);
> diff --git a/arch/xtensa/include/asm/pci.h b/arch/xtensa/include/asm/pci.h
> index 5d6bd93..f106879 100644
> --- a/arch/xtensa/include/asm/pci.h
> +++ b/arch/xtensa/include/asm/pci.h
> @@ -51,7 +51,11 @@ int pci_mmap_page_range(struct pci_dev *pdev, struct 
> vm_area_struct *vma,
>   enum pci_mmap_state mmap_state, int write_combine);
>  
>  /* Tell drivers/pci/proc.c that we have pci_mmap_page_range() */
> -#define HAVE_PCI_MMAP1
> +#define HAVE_PCI_MMAP1
> +
> +/* This was wrapped in #if 0 since the first merge of xtensa support...
> +#define arch_can_pci_mmap_wc()   1
> +*/
>  
>  #endif /* __KERNEL__ */
>  
> diff --git a/arch/xtensa/kernel/pci.c b/arch/xtensa/kernel/pci.c
> index b848cc3..c5944d3 100644
> --- a/arch/xtensa/kernel/pci.c
> +++ b/arch/xtensa/kernel/pci.c
> @@ -345,7 +345,7 @@ 

Re: [PATCH 04/17] pci: Add arch_can_pci_mmap_wc() macro

[Bjorn Helgaas]

On Wed, Mar 22, 2017 at 01:25:18PM +, David Woodhouse wrote:
> From: David Woodhouse 
> 
> 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 
> ---
>  Documentation/filesystems/sysfs-pci.txt |  4 
>  arch/ia64/include/asm/pci.h |  2 ++
>  arch/powerpc/include/asm/pci.h  |  5 +++--
>  arch/x86/include/asm/pci.h  |  2 ++
>  arch/xtensa/include/asm/pci.h   |  6 +-
>  arch/xtensa/kernel/pci.c|  2 +-
>  drivers/pci/pci-sysfs.c |  6 --
>  drivers/pci/proc.c  | 17 ++---
>  8 files changed, 31 insertions(+), 13 deletions(-)
> 
> diff --git a/Documentation/filesystems/sysfs-pci.txt 
> b/Documentation/filesystems/sysfs-pci.txt
> index 6ea1ced..25b7f1c 100644
> --- a/Documentation/filesystems/sysfs-pci.txt
> +++ b/Documentation/filesystems/sysfs-pci.txt
> @@ -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.
> diff --git a/arch/ia64/include/asm/pci.h b/arch/ia64/include/asm/pci.h
> index c0835b0..6283758 100644
> --- a/arch/ia64/include/asm/pci.h
> +++ b/arch/ia64/include/asm/pci.h
> @@ -51,6 +51,8 @@ extern unsigned long ia64_max_iommu_merge_mask;
>  #define PCI_DMA_BUS_IS_PHYS  (ia64_max_iommu_merge_mask == ~0UL)
>  
>  #define HAVE_PCI_MMAP
> +#define arch_can_pci_mmap_wc()   1
> +
>  extern int pci_mmap_page_range (struct pci_dev *dev, struct vm_area_struct 
> *vma,
>   enum pci_mmap_state mmap_state, int 
> write_combine);
>  #define HAVE_PCI_LEGACY
> diff --git a/arch/powerpc/include/asm/pci.h b/arch/powerpc/include/asm/pci.h
> index 93eded8..b5b68c6 100644
> --- a/arch/powerpc/include/asm/pci.h
> +++ b/arch/powerpc/include/asm/pci.h
> @@ -81,8 +81,9 @@ struct vm_area_struct;
>  int pci_mmap_page_range(struct pci_dev *pdev, struct vm_area_struct *vma,
>   enum pci_mmap_state mmap_state, int write_combine);
>  
> -/* Tell drivers/pci/proc.c that we have pci_mmap_page_range() */
> -#define HAVE_PCI_MMAP1
> +/* Tell drivers/pci/proc.c that we have pci_mmap_page_range() and it does WC 
> */
> +#define HAVE_PCI_MMAP1
> +#define arch_can_pci_mmap_wc()   1
>  
>  extern int pci_legacy_read(struct pci_bus *bus, loff_t port, u32 *val,
>  size_t count);
> diff --git a/arch/x86/include/asm/pci.h b/arch/x86/include/asm/pci.h
> index 1411dbe..f6e22c2 100644
> --- a/arch/x86/include/asm/pci.h
> +++ b/arch/x86/include/asm/pci.h
> @@ -7,6 +7,7 @@
>  #include 
>  #include 
>  #include 
> +#include 
>  #include 
>  
>  #ifdef __KERNEL__
> @@ -102,6 +103,7 @@ int pcibios_set_irq_routing(struct pci_dev *dev, int pin, 
> int irq);
>  
>  
>  #define HAVE_PCI_MMAP
> +#define arch_can_pci_mmap_wc()   pat_enabled()
>  extern int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct 
> *vma,
>  enum pci_mmap_state mmap_state,
>  int write_combine);
> diff --git a/arch/xtensa/include/asm/pci.h b/arch/xtensa/include/asm/pci.h
> index 5d6bd93..f106879 100644
> --- a/arch/xtensa/include/asm/pci.h
> +++ b/arch/xtensa/include/asm/pci.h
> @@ -51,7 +51,11 @@ int pci_mmap_page_range(struct pci_dev *pdev, struct 
> vm_area_struct *vma,
>   enum pci_mmap_state mmap_state, int write_combine);
>  
>  /* Tell drivers/pci/proc.c that we have pci_mmap_page_range() */
> -#define HAVE_PCI_MMAP1
> +#define HAVE_PCI_MMAP1
> +
> +/* This was wrapped in #if 0 since the first merge of xtensa support...
> +#define arch_can_pci_mmap_wc()   1
> +*/
>  
>  #endif /* __KERNEL__ */
>  
> diff --git a/arch/xtensa/kernel/pci.c b/arch/xtensa/kernel/pci.c
> index b848cc3..c5944d3 100644
> --- a/arch/xtensa/kernel/pci.c
> +++ b/arch/xtensa/kernel/pci.c
> @@ -345,7 +345,7 @@ __pci_mmap_set_pgprot(struct pci_dev *dev, struct 

[PATCH 04/17] pci: Add arch_can_pci_mmap_wc() macro

[David Woodhouse]

From: David Woodhouse 

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 
---
 Documentation/filesystems/sysfs-pci.txt |  4 
 arch/ia64/include/asm/pci.h |  2 ++
 arch/powerpc/include/asm/pci.h  |  5 +++--
 arch/x86/include/asm/pci.h  |  2 ++
 arch/xtensa/include/asm/pci.h   |  6 +-
 arch/xtensa/kernel/pci.c|  2 +-
 drivers/pci/pci-sysfs.c |  6 --
 drivers/pci/proc.c  | 17 ++---
 8 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/Documentation/filesystems/sysfs-pci.txt 
b/Documentation/filesystems/sysfs-pci.txt
index 6ea1ced..25b7f1c 100644
--- a/Documentation/filesystems/sysfs-pci.txt
+++ b/Documentation/filesystems/sysfs-pci.txt
@@ -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.
diff --git a/arch/ia64/include/asm/pci.h b/arch/ia64/include/asm/pci.h
index c0835b0..6283758 100644
--- a/arch/ia64/include/asm/pci.h
+++ b/arch/ia64/include/asm/pci.h
@@ -51,6 +51,8 @@ extern unsigned long ia64_max_iommu_merge_mask;
 #define PCI_DMA_BUS_IS_PHYS(ia64_max_iommu_merge_mask == ~0UL)
 
 #define HAVE_PCI_MMAP
+#define arch_can_pci_mmap_wc() 1
+
 extern int pci_mmap_page_range (struct pci_dev *dev, struct vm_area_struct 
*vma,
enum pci_mmap_state mmap_state, int 
write_combine);
 #define HAVE_PCI_LEGACY
diff --git a/arch/powerpc/include/asm/pci.h b/arch/powerpc/include/asm/pci.h
index 93eded8..b5b68c6 100644
--- a/arch/powerpc/include/asm/pci.h
+++ b/arch/powerpc/include/asm/pci.h
@@ -81,8 +81,9 @@ struct vm_area_struct;
 int pci_mmap_page_range(struct pci_dev *pdev, struct vm_area_struct *vma,
enum pci_mmap_state mmap_state, int write_combine);
 
-/* Tell drivers/pci/proc.c that we have pci_mmap_page_range() */
-#define HAVE_PCI_MMAP  1
+/* Tell drivers/pci/proc.c that we have pci_mmap_page_range() and it does WC */
+#define HAVE_PCI_MMAP  1
+#define arch_can_pci_mmap_wc() 1
 
 extern int pci_legacy_read(struct pci_bus *bus, loff_t port, u32 *val,
   size_t count);
diff --git a/arch/x86/include/asm/pci.h b/arch/x86/include/asm/pci.h
index 1411dbe..f6e22c2 100644
--- a/arch/x86/include/asm/pci.h
+++ b/arch/x86/include/asm/pci.h
@@ -7,6 +7,7 @@
 #include 
 #include 
 #include 
+#include 
 #include 
 
 #ifdef __KERNEL__
@@ -102,6 +103,7 @@ int pcibios_set_irq_routing(struct pci_dev *dev, int pin, 
int irq);
 
 
 #define HAVE_PCI_MMAP
+#define arch_can_pci_mmap_wc() pat_enabled()
 extern int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
   enum pci_mmap_state mmap_state,
   int write_combine);
diff --git a/arch/xtensa/include/asm/pci.h b/arch/xtensa/include/asm/pci.h
index 5d6bd93..f106879 100644
--- a/arch/xtensa/include/asm/pci.h
+++ b/arch/xtensa/include/asm/pci.h
@@ -51,7 +51,11 @@ int pci_mmap_page_range(struct pci_dev *pdev, struct 
vm_area_struct *vma,
enum pci_mmap_state mmap_state, int write_combine);
 
 /* Tell drivers/pci/proc.c that we have pci_mmap_page_range() */
-#define HAVE_PCI_MMAP  1
+#define HAVE_PCI_MMAP  1
+
+/* This was wrapped in #if 0 since the first merge of xtensa support...
+#define arch_can_pci_mmap_wc() 1
+*/
 
 #endif /* __KERNEL__ */
 
diff --git a/arch/xtensa/kernel/pci.c b/arch/xtensa/kernel/pci.c
index b848cc3..c5944d3 100644
--- a/arch/xtensa/kernel/pci.c
+++ b/arch/xtensa/kernel/pci.c
@@ -345,7 +345,7 @@ __pci_mmap_set_pgprot(struct pci_dev *dev, struct 
vm_area_struct *vma,
 
/* Set to write-through */
prot = (prot & _PAGE_CA_MASK) | _PAGE_CA_WT;
-#if 0
+#ifdef arch_can_pci_mmap_wc
if (!write_combine)
prot |= _PAGE_WRITETHRU;
 #endif
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 

[PATCH 04/17] pci: Add arch_can_pci_mmap_wc() macro

[David Woodhouse]

From: David Woodhouse 

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 
---
 Documentation/filesystems/sysfs-pci.txt |  4 
 arch/ia64/include/asm/pci.h |  2 ++
 arch/powerpc/include/asm/pci.h  |  5 +++--
 arch/x86/include/asm/pci.h  |  2 ++
 arch/xtensa/include/asm/pci.h   |  6 +-
 arch/xtensa/kernel/pci.c|  2 +-
 drivers/pci/pci-sysfs.c |  6 --
 drivers/pci/proc.c  | 17 ++---
 8 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/Documentation/filesystems/sysfs-pci.txt 
b/Documentation/filesystems/sysfs-pci.txt
index 6ea1ced..25b7f1c 100644
--- a/Documentation/filesystems/sysfs-pci.txt
+++ b/Documentation/filesystems/sysfs-pci.txt
@@ -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.
diff --git a/arch/ia64/include/asm/pci.h b/arch/ia64/include/asm/pci.h
index c0835b0..6283758 100644
--- a/arch/ia64/include/asm/pci.h
+++ b/arch/ia64/include/asm/pci.h
@@ -51,6 +51,8 @@ extern unsigned long ia64_max_iommu_merge_mask;
 #define PCI_DMA_BUS_IS_PHYS(ia64_max_iommu_merge_mask == ~0UL)
 
 #define HAVE_PCI_MMAP
+#define arch_can_pci_mmap_wc() 1
+
 extern int pci_mmap_page_range (struct pci_dev *dev, struct vm_area_struct 
*vma,
enum pci_mmap_state mmap_state, int 
write_combine);
 #define HAVE_PCI_LEGACY
diff --git a/arch/powerpc/include/asm/pci.h b/arch/powerpc/include/asm/pci.h
index 93eded8..b5b68c6 100644
--- a/arch/powerpc/include/asm/pci.h
+++ b/arch/powerpc/include/asm/pci.h
@@ -81,8 +81,9 @@ struct vm_area_struct;
 int pci_mmap_page_range(struct pci_dev *pdev, struct vm_area_struct *vma,
enum pci_mmap_state mmap_state, int write_combine);
 
-/* Tell drivers/pci/proc.c that we have pci_mmap_page_range() */
-#define HAVE_PCI_MMAP  1
+/* Tell drivers/pci/proc.c that we have pci_mmap_page_range() and it does WC */
+#define HAVE_PCI_MMAP  1
+#define arch_can_pci_mmap_wc() 1
 
 extern int pci_legacy_read(struct pci_bus *bus, loff_t port, u32 *val,
   size_t count);
diff --git a/arch/x86/include/asm/pci.h b/arch/x86/include/asm/pci.h
index 1411dbe..f6e22c2 100644
--- a/arch/x86/include/asm/pci.h
+++ b/arch/x86/include/asm/pci.h
@@ -7,6 +7,7 @@
 #include 
 #include 
 #include 
+#include 
 #include 
 
 #ifdef __KERNEL__
@@ -102,6 +103,7 @@ int pcibios_set_irq_routing(struct pci_dev *dev, int pin, 
int irq);
 
 
 #define HAVE_PCI_MMAP
+#define arch_can_pci_mmap_wc() pat_enabled()
 extern int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
   enum pci_mmap_state mmap_state,
   int write_combine);
diff --git a/arch/xtensa/include/asm/pci.h b/arch/xtensa/include/asm/pci.h
index 5d6bd93..f106879 100644
--- a/arch/xtensa/include/asm/pci.h
+++ b/arch/xtensa/include/asm/pci.h
@@ -51,7 +51,11 @@ int pci_mmap_page_range(struct pci_dev *pdev, struct 
vm_area_struct *vma,
enum pci_mmap_state mmap_state, int write_combine);
 
 /* Tell drivers/pci/proc.c that we have pci_mmap_page_range() */
-#define HAVE_PCI_MMAP  1
+#define HAVE_PCI_MMAP  1
+
+/* This was wrapped in #if 0 since the first merge of xtensa support...
+#define arch_can_pci_mmap_wc() 1
+*/
 
 #endif /* __KERNEL__ */
 
diff --git a/arch/xtensa/kernel/pci.c b/arch/xtensa/kernel/pci.c
index b848cc3..c5944d3 100644
--- a/arch/xtensa/kernel/pci.c
+++ b/arch/xtensa/kernel/pci.c
@@ -345,7 +345,7 @@ __pci_mmap_set_pgprot(struct pci_dev *dev, struct 
vm_area_struct *vma,
 
/* Set to write-through */
prot = (prot & _PAGE_CA_MASK) | _PAGE_CA_WT;
-#if 0
+#ifdef arch_can_pci_mmap_wc
if (!write_combine)
prot |= _PAGE_WRITETHRU;
 #endif
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 7ac258f..cf2c7d8 100644
---