Some devices may not support entire 64bit DMA. In a situation where such 
devices are co-located in a shared domain, we need to ensure there is some 
address space reserved for such devices without the low addresses getting
depleted by other devices capable of handling high dma addresses.

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Index: linux-2.6.21-rc5/Documentation/kernel-parameters.txt
===================================================================
--- linux-2.6.21-rc5.orig/Documentation/kernel-parameters.txt	2007-04-09 03:05:38.000000000 -0700
+++ linux-2.6.21-rc5/Documentation/kernel-parameters.txt	2007-04-09 03:05:41.000000000 -0700
@@ -735,6 +735,11 @@
 			first 16M. The floppy disk could be modified to use
 			the DMA api's but thats a lot of pain for very small
 			gain. This option is turned on by default.
+		preserve_{1g/2g/4g/512m/256m/16m}
+			If a device is sharing a domain with other devices
+			and the device mask doesnt cover the 64bit range,
+			use this option to let the iommu code preserve some
+			virtual addr for such devices.
 	io7=		[HW] IO7 for Marvel based alpha systems
 			See comment before marvel_specify_io7 in
 			arch/alpha/kernel/core_marvel.c.
Index: linux-2.6.21-rc5/drivers/pci/intel-iommu.c
===================================================================
--- linux-2.6.21-rc5.orig/drivers/pci/intel-iommu.c	2007-04-09 03:05:38.000000000 -0700
+++ linux-2.6.21-rc5/drivers/pci/intel-iommu.c	2007-04-09 03:06:17.000000000 -0700
@@ -90,6 +90,7 @@
 static int dmar_disabled, dmar_force_rw;
 static int dmar_map_gfx = 1, dmar_no_gfx_identity_map = 1;
 static int dmar_fix_isa = 1;
+static u64 dmar_preserve_iova_mask;
 
 static char *get_fault_reason(u8 fault_reason)
 {
@@ -119,6 +120,28 @@
 		} else if (!strncmp(str, "noisamap", 8)) {
 			dmar_fix_isa = 0;
 			printk (KERN_INFO"Intel-IOMMU: Turning off 16M unity map for LPC\n");
+ 		} else if (!strncmp(str, "preserve_", 9)) {
+ 			if (!strncmp(str + 9, "4g", 2) ||
+ 			    !strncmp(str + 9, "4G", 2))
+ 				dmar_preserve_iova_mask = DMA_32BIT_MASK;
+ 			else if (!strncmp(str + 9, "2g", 2) ||
+ 				!strncmp(str + 9, "2G", 2))
+ 				dmar_preserve_iova_mask = DMA_31BIT_MASK;
+ 			else if (!strncmp(str + 9, "1g", 2) ||
+ 			         !strncmp(str + 9, "1G", 2))
+ 				dmar_preserve_iova_mask = DMA_30BIT_MASK;
+ 			else if (!strncmp(str + 9, "512m", 2) ||
+ 			         !strncmp(str + 9, "512M", 2))
+ 				dmar_preserve_iova_mask = DMA_29BIT_MASK;
+ 			else if (!strncmp(str + 9, "256m", 4) ||
+ 			         !strncmp(str + 9, "256M", 4))
+ 				dmar_preserve_iova_mask = DMA_28BIT_MASK;
+ 			else if (!strncmp(str + 9, "16m", 3) ||
+ 			         !strncmp(str + 9, "16M", 3))
+ 				dmar_preserve_iova_mask = DMA_24BIT_MASK;
+			printk(KERN_INFO
+ 			"DMAR: Preserved IOVA mask 0x%Lx for devices "
+ 			"sharing domain\n", dmar_preserve_iova_mask);
 		}
 
 		str += strcspn(str, ",");
@@ -1726,9 +1749,10 @@
 	 * leave rooms for other devices
 	 */
 	if ((domain->flags & DOMAIN_FLAG_MULTIPLE_DEVICES) &&
-			pdev->dma_mask > DMA_32BIT_MASK)
+			dmar_preserve_iova_mask &&
+			pdev->dma_mask > dmar_preserve_iova_mask)
 		iova = alloc_iova(domain, addr, size,
-				DMA_32BIT_MASK + 1, pdev->dma_mask);
+				dmar_preserve_iova_mask + 1, pdev->dma_mask);
 	else
 		iova = alloc_iova(domain, addr, size,
 				IOVA_START_ADDR, pdev->dma_mask);

-- 
-
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