[PATCH] tentative fix for radeon on systems >4GB without hardware iommu

[Daniel Haid <d.haid@gogi.tv>]

 On my x86_64 system with >4GB of ram and swiotlb instead of
 a hardware iommu (because I have a VIA chipset), the call
 to pci_set_dma_mask (see below) with 40bits returns an error.

 But it seems that the radeon driver is designed to have
 need_dma32 = true exactly if pci_set_dma_mask is called
 with 32 bits and false if it is called with 40 bits.

 I have read somewhere that the default are 32 bits. So if the
 call fails I suppose that need_dma32 should be set to true.

 And indeed the patch fixes the problem I have had before
 and which I had described here:
 http://choon.net/forum/read.php?21,106131,115940

 --- 
 linux-2.6.39-gentoo/drivers/gpu/drm/radeon/radeon_device.c.old	2011-06-03 
 19:11:33.208891994 +0200
 +++ 
 linux-2.6.39-gentoo/drivers/gpu/drm/radeon/radeon_device.c	2011-06-03 
 19:21:10.240337986 +0200
 @@ -752,6 +752,7 @@ int radeon_device_init(struct radeon_dev
  	dma_bits = rdev->need_dma32 ? 32 : 40;
  	r = pci_set_dma_mask(rdev->pdev, DMA_BIT_MASK(dma_bits));
  	if (r) {
 +		rdev->need_dma32 = true;
  		printk(KERN_WARNING "radeon: No suitable DMA available.\n");
  	}