x86/PCI: Adjust GFP mask handling for coherent allocations

Rather than forcing GFP flags and DMA mask to be inconsistent,
GFP flags should be determined even for the fallback device
through dma_alloc_coherent_mask()/dma_alloc_coherent_gfp_flags().

This restores 64-bit behavior as it was prior to commits
8965eb19386fdf5ccd0ef8b02593eb8560aa3416 and
4a367f3a9dbf2e7ffcee4702203479809236ee6e (not sure why there are
two of them), where GFP_DMA was forced on for 32-bit, but not
for 64-bit, with the slight adjustment that afaict even 32-bit
doesn't need this without CONFIG_ISA.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Acked-by: Takashi Iwai <tiwai@suse.de>
LKML-Reference: <4AF18187020000780001D8AA@vpn.id2.novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

arch/x86/include/asm/dma-mapping.h

@@ -14,6 +14,12 @@
 #include <asm/swiotlb.h>
 #include <asm-generic/dma-coherent.h>
 
+#ifdef CONFIG_ISA
+# define ISA_DMA_BIT_MASK DMA_BIT_MASK(24)
+#else
+# define ISA_DMA_BIT_MASK DMA_BIT_MASK(32)
+#endif
+
 extern dma_addr_t bad_dma_address;
 extern int iommu_merge;
 extern struct device x86_dma_fallback_dev;
@@ -124,10 +130,8 @@ dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle,
 	if (dma_alloc_from_coherent(dev, size, dma_handle, &memory))
 		return memory;
 
-	if (!dev) {
+	if (!dev)
 		dev = &x86_dma_fallback_dev;
-		gfp |= GFP_DMA;
-	}
 
 	if (!is_device_dma_capable(dev))
 		return NULL;

arch/x86/kernel/pci-dma.c

@@ -45,12 +45,10 @@ int iommu_pass_through __read_mostly;
 dma_addr_t bad_dma_address __read_mostly = 0;
 EXPORT_SYMBOL(bad_dma_address);
 
-/* Dummy device used for NULL arguments (normally ISA). Better would
-   be probably a smaller DMA mask, but this is bug-to-bug compatible
-   to older i386. */
+/* Dummy device used for NULL arguments (normally ISA). */
 struct device x86_dma_fallback_dev = {
 	.init_name = "fallback device",
-	.coherent_dma_mask = DMA_BIT_MASK(32),
+	.coherent_dma_mask = ISA_DMA_BIT_MASK,
 	.dma_mask = &x86_dma_fallback_dev.coherent_dma_mask,
 };
 EXPORT_SYMBOL(x86_dma_fallback_dev);