m68k: Use the generic dma coherent remap allocator

This switches m68k to using common code for the DMA allocations,
including potential use of the CMA allocator if configured.
Also add a comment where the existing behavior seems to be lacking.

Switching to the generic code enables DMA allocations from atomic
context, which is required by the DMA API documentation, and also
adds various other minor features drivers start relying upon.  It
also makes sure we have a tested code base for all architectures
that require uncached pte bits for coherent DMA allocations.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/Kconfig

@@ -3,10 +3,12 @@ config M68K
 	bool
 	default y
 	select ARCH_32BIT_OFF_T
+	select ARCH_HAS_DMA_MMAP_PGPROT if MMU && !COLDFIRE
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE if HAS_DMA
 	select ARCH_MIGHT_HAVE_PC_PARPORT if ISA
 	select ARCH_NO_COHERENT_DMA_MMAP if !MMU
 	select ARCH_NO_PREEMPT if !COLDFIRE
+	select DMA_DIRECT_REMAP if HAS_DMA && MMU && !COLDFIRE
 	select HAVE_IDE
 	select HAVE_AOUT if MMU
 	select HAVE_DEBUG_BUGVERBOSE

arch/m68k/kernel/dma.c

@@ -18,57 +18,17 @@
 #include <asm/pgalloc.h>
 
 #if defined(CONFIG_MMU) && !defined(CONFIG_COLDFIRE)
-
-void *arch_dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
-		gfp_t flag, unsigned long attrs)
+pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
+		unsigned long attrs)
 {
-	struct page *page, **map;
-	pgprot_t pgprot;
-	void *addr;
-	int i, order;
-
-	pr_debug("dma_alloc_coherent: %d,%x\n", size, flag);
-
-	size = PAGE_ALIGN(size);
-	order = get_order(size);
-
-	page = alloc_pages(flag | __GFP_ZERO, order);
-	if (!page)
-		return NULL;
-
-	*handle = page_to_phys(page);
-	map = kmalloc(sizeof(struct page *) << order, flag & ~__GFP_DMA);
-	if (!map) {
-		__free_pages(page, order);
-		return NULL;
+	if (CPU_IS_040_OR_060) {
+		pgprot_val(prot) &= ~_PAGE_CACHE040;
+		pgprot_val(prot) |= _PAGE_GLOBAL040 | _PAGE_NOCACHE_S;
+	} else {
+		pgprot_val(prot) |= _PAGE_NOCACHE030;
 	}
-	split_page(page, order);
-
-	order = 1 << order;
-	size >>= PAGE_SHIFT;
-	map[0] = page;
-	for (i = 1; i < size; i++)
-		map[i] = page + i;
-	for (; i < order; i++)
-		__free_page(page + i);
-	pgprot = __pgprot(_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_DIRTY);
-	if (CPU_IS_040_OR_060)
-		pgprot_val(pgprot) |= _PAGE_GLOBAL040 | _PAGE_NOCACHE_S;
-	else
-		pgprot_val(pgprot) |= _PAGE_NOCACHE030;
-	addr = vmap(map, size, VM_MAP, pgprot);
-	kfree(map);
-
-	return addr;
+	return prot;
 }
-
-void arch_dma_free(struct device *dev, size_t size, void *addr,
-		dma_addr_t handle, unsigned long attrs)
-{
-	pr_debug("dma_free_coherent: %p, %x\n", addr, handle);
-	vfree(addr);
-}
-
 #else
 
 #include <asm/cacheflush.h>