Xen devel - May 2013 - [PATCH Xen-4.2] AMD/iommu: SR56x0 Erratum 64 - Reset all head & tail pointers

Reference at time of patch:
http://support.amd.com/us/ChipsetMotherboard_TechDocs/46303.pdf

Erratum 64 states that the head and tail pointers for the Command buffer and
Event log are only reset on a cold boot, not a warm boot.

While the erratum is limited to systems using SR56xx chipsets (such as Family
10h CPUs), resetting the pointers is a sensible action in all cases, including
the PPR log for consistency.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

--

Changes since v1:
 * Reset PPR head/tail pointer as well

diff -r 914f6b933621 -r 12e272d21c4a xen/drivers/passthrough/amd/iommu_init.c
--- a/xen/drivers/passthrough/amd/iommu_init.c
+++ b/xen/drivers/passthrough/amd/iommu_init.c
@@ -154,6 +154,11 @@ static void register_iommu_cmd_buffer_in
                          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)
@@ -182,6 +187,11 @@ static void register_iommu_event_log_in_
                         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 register_iommu_ppr_log_in_mmio_space(struct amd_iommu *iommu)
@@ -210,6 +220,9 @@ static void register_iommu_ppr_log_in_mm
                         IOMMU_PPR_LOG_LENGTH_MASK,
                         IOMMU_PPR_LOG_LENGTH_SHIFT, &entry);
     writel(entry, iommu->mmio_base + IOMMU_PPR_LOG_BASE_HIGH_OFFSET);
+
+    writel(0, iommu->mmio_base + IOMMU_PPR_LOG_HEAD_OFFSET);
+    writel(0, iommu->mmio_base + IOMMU_PPR_LOG_TAIL_OFFSET);
 }