drm/i915/ringbuffer: Handle wrapping of the autoreported HEAD
If the tail advances beyond the autoreport HEAD value, then we need to
fallback to an uncached read of the HEAD register in order to ascertain
the correct amount of remaining space in the ringbuffer.
Reported-by: Fang, Xun <xunx.fang@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=32259
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 89a65be..31cd7e3 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -696,20 +696,17 @@
drm_i915_private_t *dev_priv = dev->dev_private;
u32 head;
- head = intel_read_status_page(ring, 4);
- if (head) {
- ring->head = head & HEAD_ADDR;
- ring->space = ring->head - (ring->tail + 8);
- if (ring->space < 0)
- ring->space += ring->size;
- if (ring->space >= n)
- return 0;
- }
-
trace_i915_ring_wait_begin (dev);
end = jiffies + 3 * HZ;
do {
- ring->head = I915_READ_HEAD(ring) & HEAD_ADDR;
+ /* If the reported head position has wrapped or hasn't advanced,
+ * fallback to the slow and accurate path.
+ */
+ head = intel_read_status_page(ring, 4);
+ if (head < ring->actual_head)
+ head = I915_READ_HEAD(ring);
+ ring->actual_head = head;
+ ring->head = head & HEAD_ADDR;
ring->space = ring->head - (ring->tail + 8);
if (ring->space < 0)
ring->space += ring->size;