[PATCH] Stop pci_set_dma_mask() from failing when RAM doesn't exceed the mask anyway

[David Woodhouse <dwmw2@infradead.org>]

On an iMac G5, the b43 driver is failing to initialise because trying to
set the dma mask to 30-bit fails. Even though there's only 512MiB of RAM
in the machine anyway:
	https://bugzilla.redhat.com/show_bug.cgi?id=514787

We should probably let it succeed if the available RAM in the system
doesn't exceed the requested limit.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

diff --git a/arch/powerpc/kernel/dma.c b/arch/powerpc/kernel/dma.c
index 20a60d6..1769a8e 100644
--- a/arch/powerpc/kernel/dma.c
+++ b/arch/powerpc/kernel/dma.c
@@ -90,11 +90,11 @@ static void dma_direct_unmap_sg(struct device *dev,
struct scatterlist *sg,
 static int dma_direct_dma_supported(struct device *dev, u64 mask)
 {
 #ifdef CONFIG_PPC64
-	/* Could be improved to check for memory though it better be
-	 * done via some global so platforms can set the limit in case
+	extern unsigned long highest_memmap_pfn;
+	/* Could be improved so platforms can set the limit in case
 	 * they have limited DMA windows
 	 */
-	return mask >= DMA_BIT_MASK(32);
+	return (mask >> PAGE_SHIFT) >= highest_memmap_pfn;
 #else
 	return 1;
 #endif

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation