[PATCH v12 3/10] x86, asm: Change is_new_memtype_allowed() for WT

[Toshi Kani <toshi.kani@hp.com>]

__ioremap_caller() calls reserve_memtype() to set new_pcm
(existing map type if any), and then calls
is_new_memtype_allowed() to verify if converting to new_pcm
is allowed when pcm (request type) is different from new_pcm.

When WT is requested, the caller expects that writes are
ordered and uncached.  Therefore, this patch changes
is_new_memtype_allowed() to disallow the following cases.

 - If the request is WT, mapping type cannot be WB
 - If the request is WT, mapping type cannot be WC

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/include/asm/pgtable.h |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index fe57e7a..2562e30 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -398,11 +398,17 @@ static inline int is_new_memtype_allowed(u64 paddr, unsigned long size,
 	 * requested memtype:
 	 * - request is uncached, return cannot be write-back
 	 * - request is write-combine, return cannot be write-back
+	 * - request is write-through, return cannot be write-back
+	 * - request is write-through, return cannot be write-combine
 	 */
 	if ((pcm == _PAGE_CACHE_MODE_UC_MINUS &&
 	     new_pcm == _PAGE_CACHE_MODE_WB) ||
 	    (pcm == _PAGE_CACHE_MODE_WC &&
-	     new_pcm == _PAGE_CACHE_MODE_WB)) {
+	     new_pcm == _PAGE_CACHE_MODE_WB) ||
+	    (pcm == _PAGE_CACHE_MODE_WT &&
+	     new_pcm == _PAGE_CACHE_MODE_WB) ||
+	    (pcm == _PAGE_CACHE_MODE_WT &&
+	     new_pcm == _PAGE_CACHE_MODE_WC)) {
 		return 0;
 	}