x86: PAT: add pgprot_writecombine() interface for drivers - v3

Impact: New mm functionality.

Add pgprot_writecombine. pgprot_writecombine will be aliased to
pgprot_noncached when not supported by the architecture.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

2 files changed, 11 insertions, 0 deletions

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 6968d4f6be3e..579f8ceee948 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -168,6 +168,9 @@
 
 #ifndef __ASSEMBLY__
 
+#define pgprot_writecombine     pgprot_writecombine
+extern pgprot_t pgprot_writecombine(pgprot_t prot);
+
 /*
  * ZERO_PAGE is a global shared page that is always zero: used
  * for zero-mapped memory areas etc..
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 1069ffecf77d..d5254bae84f4 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -832,6 +832,14 @@ void untrack_pfn_vma(struct vm_area_struct *vma, unsigned long pfn,
         }
 }
 
+pgprot_t pgprot_writecombine(pgprot_t prot)
+{
+        if (pat_enabled)
+                return __pgprot(pgprot_val(prot) | _PAGE_CACHE_WC);
+        else
+                return pgprot_noncached(prot);
+}
+
 #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_X86_PAT)
 
 /* get Nth element of the linked list */