[ARM] 3439/2: xsc3: add I/O coherency support

Patch from Lennert Buytenhek

This patch adds support for the I/O coherent cache available on the
xsc3.  The approach is to provide a simple API to determine whether the
chipset supports coherency by calling arch_is_coherent() and then
setting the appropriate system memory PTE and PMD bits.  In addition,
we call this API on dma_alloc_coherent() and dma_map_single() calls.
A generic version exists that will compile out all the coherency-related
code that is not needed on the majority of ARM systems.

Note that we do not check for coherency in the dma_alloc_writecombine()
function as that still requires a special PTE setting.  We also don't
touch dma_mmap_coherent() as that is a special ARM-only API that is by
definition only used on non-coherent system.

Signed-off-by: Deepak Saxena <dsaxena@plexity.net>
Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/mm-armv.c

@@ -388,6 +388,17 @@ void __init build_mem_type_table(void)
 	cp = &cache_policies[cachepolicy];
 	kern_pgprot = user_pgprot = cp->pte;
 
+	/*
+	 * Enable CPU-specific coherency if supported.
+	 * (Only available on XSC3 at the moment.)
+	 */
+	if (arch_is_coherent()) {
+		if (cpu_is_xsc3()) {
+			mem_types[MT_MEMORY].prot_sect |= PMD_SECT_S;
+			mem_types[MT_MEMORY].prot_pte |= L_PTE_COHERENT;
+		}
+	}
+
 	/*
 	 * ARMv6 and above have extended page tables.
 	 */