2 files changed, 11 insertions, 3 deletions

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 56bc95c056dd..2de0e45464c5 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -785,6 +785,14 @@ int intel_init_ring_buffer(struct drm_device *dev,
         if (ret)
                 goto err_unmap;
 
+        /* Workaround an erratum on the i830 which causes a hang if
+         * the TAIL pointer points to within the last 2 cachelines
+         * of the buffer.
+         */
+        ring->effective_size = ring->size;
+        if (IS_I830(ring->dev))
+                ring->effective_size -= 128;
+
         return 0;
 
 err_unmap:
@@ -827,8 +835,7 @@ void intel_cleanup_ring_buffer(struct intel_ring_buffer *ring)
 static int intel_wrap_ring_buffer(struct intel_ring_buffer *ring)
 {
         unsigned int *virt;
-        int rem;
-        rem = ring->size - ring->tail;
+        int rem = ring->size - ring->tail;
 
         if (ring->space < rem) {
                 int ret = intel_wait_ring_buffer(ring, rem);
@@ -895,7 +902,7 @@ int intel_ring_begin(struct intel_ring_buffer *ring,
         int n = 4*num_dwords;
         int ret;
 
-        if (unlikely(ring->tail + n > ring->size)) {
+        if (unlikely(ring->tail + n > ring->effective_size)) {
                 ret = intel_wrap_ring_buffer(ring);
                 if (unlikely(ret))
                         return ret;
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 8e2e357ad6ee..bbbf505c8b56 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -49,6 +49,7 @@ struct  intel_ring_buffer {
         u32             tail;
         int             space;
         int             size;
+        int             effective_size;
         struct intel_hw_status_page status_page;
 
         u32             irq_seqno;              /* last seq seem at irq time */