From 09067207f6eacb7f00c8f7f0623c3696083ce042 Mon Sep 17 00:00:00 2001
From: Joerg Roedel <joerg.roedel@amd.com>
Date: Mon, 15 Jun 2009 16:06:48 +0200
Subject: amd-iommu: set event buffer head and tail to 0 manually

These registers may contain values from previous kernels. So reset them
to known values before enable the event buffer again.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

diff --git a/arch/x86/kernel/amd_iommu_init.c b/arch/x86/kernel/amd_iommu_init.c
index 48a79b9..068a356 100644
--- a/arch/x86/kernel/amd_iommu_init.c
+++ b/arch/x86/kernel/amd_iommu_init.c
@@ -486,6 +486,10 @@ static void iommu_enable_event_buffer(struct amd_iommu *iommu)
 	memcpy_toio(iommu->mmio_base + MMIO_EVT_BUF_OFFSET,
 		    &entry, sizeof(entry));
 
+	/* set head and tail to zero manually */
+	writel(0x00, iommu->mmio_base + MMIO_EVT_HEAD_OFFSET);
+	writel(0x00, iommu->mmio_base + MMIO_EVT_TAIL_OFFSET);
+
 	iommu_feature_enable(iommu, CONTROL_EVT_LOG_EN);
 }
 
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