linux-kernel - [PATCH 1/8] x86/dma: Mark iommu_pass_through as __read

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Message-ID: <1252056994-31980-2-git-send-email-joerg.roedel@amd.com>
Date:	Fri, 4 Sep 2009 11:36:27 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
CC:	Joerg Roedel <joerg.roedel@....com>
Subject: [PATCH 1/8] x86/dma: Mark iommu_pass_through as __read_mostly

This variable is read most of the time. This patch marks it
as such. It also documents the meaning the this variable
while at it.

Signed-off-by: Joerg Roedel <joerg.roedel@....com>
---
 arch/x86/kernel/pci-dma.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index 1a041bc..873aa07 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -32,7 +32,14 @@ int no_iommu __read_mostly;
 /* Set this to 1 if there is a HW IOMMU in the system */
 int iommu_detected __read_mostly = 0;
 
-int iommu_pass_through;
+/*
+ * This variable becomes 1 if iommu=pt is passed on the kernel command line.
+ * If this variable is 1, IOMMU implementations do no DMA ranslation for
+ * devices and allow every device to access to whole physical memory. This is
+ * useful if a user want to use an IOMMU only for KVM device assignment to
+ * guests and not for driver dma translation.
+ */
+int iommu_pass_through __read_mostly;
 
 dma_addr_t bad_dma_address __read_mostly = 0;
 EXPORT_SYMBOL(bad_dma_address);
-- 
1.6.3.3


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