Revert "AMD/iommu: SR56x0 Erratum 64 - Reset all head & tail pointers"

This reverts commit 22de18bb89.

The code this patch added is redundant with already present code in
set_iommu_{command_buffer,event_log}_control().

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>

master commit: e430510e5c
master date: 2013-06-05 10:05:49 +0200

xen/drivers/passthrough/amd/iommu_init.c

@@ -119,11 +119,6 @@ static void register_iommu_cmd_buffer_in_mmio_space(struct amd_iommu *iommu)
                          IOMMU_CMD_BUFFER_LENGTH_MASK,
                          IOMMU_CMD_BUFFER_LENGTH_SHIFT, &entry);
     writel(entry, iommu->mmio_base+IOMMU_CMD_BUFFER_BASE_HIGH_OFFSET);
-
-    /* Reset head/tail pointer. SR56x0 Erratum 64 means this might not happen
-     * automatically for us. */
-    writel(0, iommu->mmio_base + IOMMU_CMD_BUFFER_HEAD_OFFSET);
-    writel(0, iommu->mmio_base + IOMMU_CMD_BUFFER_TAIL_OFFSET);
 }
 
 static void register_iommu_event_log_in_mmio_space(struct amd_iommu *iommu)
@@ -151,11 +146,6 @@ static void register_iommu_event_log_in_mmio_space(struct amd_iommu *iommu)
                         IOMMU_EVENT_LOG_LENGTH_MASK,
                         IOMMU_EVENT_LOG_LENGTH_SHIFT, &entry);
     writel(entry, iommu->mmio_base+IOMMU_EVENT_LOG_BASE_HIGH_OFFSET);
-
-    /* Reset head/tail pointer. SR56x0 Erratum 64 means this might not happen
-     * automatically for us. */
-    writel(0, iommu->mmio_base + IOMMU_EVENT_LOG_HEAD_OFFSET);
-    writel(0, iommu->mmio_base + IOMMU_EVENT_LOG_TAIL_OFFSET);
 }
 
 static void set_iommu_translation_control(struct amd_iommu *iommu,