From be2602ba7152b3e2557d192c2f2a5a91d4d29e3d Mon Sep 17 00:00:00 2001
From: David Vrabel <david.vrabel@citrix.com>
Date: Fri, 9 May 2014 11:40:46 +0100
Subject: [PATCH 2/2] x86,xen: correct dma_get_required_mask() for Xen PV guests

On systems where DMA addresses and physical addresses are not 1:1
(such as Xen PV guests), the generic dma_get_required_mask() will not
return the correct mask (since it uses max_pfn).

Some device drivers (such as mptsas, mpt2sas) use
dma_get_required_mask() to set device DMA masks to allow them to use
only 32-bit DMA addresses in hardware structures.  This results in
unnecessary use of the SWIOTLB if DMA addresses are more than 32-bits,
impacting performance significantly.

Provide an arch-specific dma_get_required_mask() that defaults to the
generic dma_get_required_mask_from_pfn().

Under Xen, the required DMA mask can then be set to always 64-bits.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
diff --git a/arch/x86/include/asm/device.h b/arch/x86/include/asm/device.h
index 03dd729..10bc628 100644
--- a/arch/x86/include/asm/device.h
+++ b/arch/x86/include/asm/device.h
@@ -13,4 +13,6 @@ struct dev_archdata {
 struct pdev_archdata {
 };
 
+#define ARCH_HAS_DMA_GET_REQUIRED_MASK
+
 #endif /* _ASM_X86_DEVICE_H */
diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index f7d0672..3423da9 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -135,6 +135,14 @@ void dma_generic_free_coherent(struct device *dev, size_t size, void *vaddr,
 		free_pages((unsigned long)vaddr, get_order(size));
 }
 
+u64 dma_get_required_mask(struct device *dev)
+{
+	if (dma_ops->get_required_mask)
+		return dma_ops->get_required_mask(dev);
+	return dma_get_required_mask_from_max_pfn(dev);
+}
+EXPORT_SYMBOL_GPL(dma_get_required_mask);
+
 /*
  * See <Documentation/x86/x86_64/boot-options.txt> for the iommu kernel
  * parameter documentation.
diff --git a/arch/x86/xen/pci-swiotlb-xen.c b/arch/x86/xen/pci-swiotlb-xen.c
index 9695704..98eef08 100644
--- a/arch/x86/xen/pci-swiotlb-xen.c
+++ b/arch/x86/xen/pci-swiotlb-xen.c
@@ -31,6 +31,7 @@ static struct dma_map_ops xen_swiotlb_dma_ops = {
 	.map_page = xen_swiotlb_map_page,
 	.unmap_page = xen_swiotlb_unmap_page,
 	.dma_supported = xen_swiotlb_dma_supported,
+	.get_required_mask = xen_swiotlb_get_required_mask,
 };
 
 /*
diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 07a9b9e..92cc199 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -596,3 +596,10 @@ xen_swiotlb_dma_supported(struct device *hwdev, u64 mask)
 	return xen_virt_to_bus(xen_io_tlb_end - 1) <= mask;
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_dma_supported);
+
+u64
+xen_swiotlb_get_required_mask(struct device *dev)
+{
+	return DMA_BIT_MASK(64);
+}
+EXPORT_SYMBOL_GPL(xen_swiotlb_get_required_mask);
diff --git a/include/xen/swiotlb-xen.h b/include/xen/swiotlb-xen.h
index de8bcc6..e08d8bd 100644
--- a/include/xen/swiotlb-xen.h
+++ b/include/xen/swiotlb-xen.h
@@ -55,4 +55,7 @@ xen_swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr);
 extern int
 xen_swiotlb_dma_supported(struct device *hwdev, u64 mask);
 
+extern u64
+xen_swiotlb_get_required_mask(struct device *dev);
+
 #endif /* __LINUX_SWIOTLB_XEN_H */