x86: restore old GART alloc_coherent behavior

Currently, GART alloc_coherent tries to allocate pages with GFP_DMA32
for a device having dma_masks > 24bit < 32bits. If GART gets an
address that a device can't access to, GART try to map the address to
a virtual I/O address that the device can access to.

But Andi pointed out, "The GART is somewhere in the 4GB range so you
cannot use it to map anything < 4GB. Also GART is pretty small."

http://lkml.org/lkml/2008/9/12/43

That is, it's possible that GART doesn't have virtual I/O address
space that a device can access to. The above behavior doesn't work for
a device having dma_masks > 24bit < 32bits.

This patch restores old GART alloc_coherent behavior (before the
alloc_coherent rewrite).

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/pci-gart_64.c

@@ -487,31 +487,28 @@ static void *
 gart_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_addr,
 		    gfp_t flag)
 {
-	void *vaddr;
 	dma_addr_t paddr;
 	unsigned long align_mask;
-	u64 dma_mask = dma_alloc_coherent_mask(dev, flag);
+	struct page *page;
 
-	vaddr = (void *)__get_free_pages(flag | __GFP_ZERO, get_order(size));
-	if (!vaddr)
-		return NULL;
+	if (force_iommu && !(flag & GFP_DMA)) {
+		flag &= ~(__GFP_DMA | __GFP_HIGHMEM | __GFP_DMA32);
+		page = alloc_pages(flag | __GFP_ZERO, get_order(size));
+		if (!page)
+			return NULL;
 
-	paddr = virt_to_phys(vaddr);
-	if (is_buffer_dma_capable(dma_mask, paddr, size)) {
-		*dma_addr = paddr;
-		return vaddr;
-	}
+		align_mask = (1UL << get_order(size)) - 1;
+		paddr = dma_map_area(dev, page_to_phys(page), size,
+				     DMA_BIDIRECTIONAL, align_mask);
 
-	align_mask = (1UL << get_order(size)) - 1;
-
-	*dma_addr = dma_map_area(dev, paddr, size, DMA_BIDIRECTIONAL,
-				 align_mask);
-	flush_gart();
-
-	if (*dma_addr != bad_dma_address)
-		return vaddr;
-
-	free_pages((unsigned long)vaddr, get_order(size));
+		flush_gart();
+		if (paddr != bad_dma_address) {
+			*dma_addr = paddr;
+			return page_address(page);
+		}
+		__free_pages(page, get_order(size));
+	} else
+		return dma_generic_alloc_coherent(dev, size, dma_addr, flag);
 
 	return NULL;
 }