iommu/amd: Add workaround for event log erratum

Due to a recent erratum it can happen that the head pointer
of the event-log is updated before the actual event-log
entry is written. This patch implements the recommended
workaround.

Cc: stable@vger.kernel.org	# all stable kernels
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

1 files changed, 23 insertions, 6 deletions

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 08f3eecb87a2..d90a421e9cac 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -450,12 +450,27 @@ static void dump_command(unsigned long phys_addr)
 
 static void iommu_print_event(struct amd_iommu *iommu, void *__evt)
 {
-        u32 *event = __evt;
-        int type  = (event[1] >> EVENT_TYPE_SHIFT)  & EVENT_TYPE_MASK;
-        int devid = (event[0] >> EVENT_DEVID_SHIFT) & EVENT_DEVID_MASK;
-        int domid = (event[1] >> EVENT_DOMID_SHIFT) & EVENT_DOMID_MASK;
-        int flags = (event[1] >> EVENT_FLAGS_SHIFT) & EVENT_FLAGS_MASK;
-        u64 address = (u64)(((u64)event[3]) << 32) | event[2];
+        int type, devid, domid, flags;
+        volatile u32 *event = __evt;
+        int count = 0;
+        u64 address;
+
+retry:
+        type    = (event[1] >> EVENT_TYPE_SHIFT)  & EVENT_TYPE_MASK;
+        devid   = (event[0] >> EVENT_DEVID_SHIFT) & EVENT_DEVID_MASK;
+        domid   = (event[1] >> EVENT_DOMID_SHIFT) & EVENT_DOMID_MASK;
+        flags   = (event[1] >> EVENT_FLAGS_SHIFT) & EVENT_FLAGS_MASK;
+        address = (u64)(((u64)event[3]) << 32) | event[2];
+
+        if (type == 0) {
+                /* Did we hit the erratum? */
+                if (++count == LOOP_TIMEOUT) {
+                        pr_err("AMD-Vi: No event written to event log\n");
+                        return;
+                }
+                udelay(1);
+                goto retry;
+        }
 
         printk(KERN_ERR "AMD-Vi: Event logged [");
 
@@ -508,6 +523,8 @@ static void iommu_print_event(struct amd_iommu *iommu, void *__evt)
         default:
                 printk(KERN_ERR "UNKNOWN type=0x%02x]\n", type);
         }
+
+        memset(__evt, 0, 4 * sizeof(u32));
 }
 
 static void iommu_poll_events(struct amd_iommu *iommu)