powerpc: Fix up dma_alloc_coherent() on platforms without cache coherency.

The implementation we just revived has issues, such as using a
Kconfig-defined virtual address area in kernel space that nothing
actually carves out (and thus will overlap whatever is there),
or having some dependencies on being self contained in a single
PTE page which adds unnecessary constraints on the kernel virtual
address space.

This fixes it by using more classic PTE accessors and automatically
locating the area for consistent memory, carving an appropriate hole
in the kernel virtual address space, leaving only the size of that
area as a Kconfig option. It also brings some dma-mask related fixes
from the ARM implementation which was almost identical initially but
grew its own fixes.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/pgtable-ppc32.h b/arch/powerpc/include/asm/pgtable-ppc32.h
index 28fe9d4bae35..c9ff9d75990e 100644
--- a/arch/powerpc/include/asm/pgtable-ppc32.h
+++ b/arch/powerpc/include/asm/pgtable-ppc32.h
@@ -71,7 +71,11 @@ extern int icache_44x_need_flush;
  * until mem_init() at which point this becomes the top of the vmalloc
  * and ioremap space
  */
+#ifdef CONFIG_NOT_COHERENT_CACHE
+#define IOREMAP_TOP     ((KVIRT_TOP - CONFIG_CONSISTENT_SIZE) & PAGE_MASK)
+#else
 #define IOREMAP_TOP     KVIRT_TOP
+#endif
 
 /*
  * Just any arbitrary offset to the start of the vmalloc VM area: the