drm/i915: Wrap around the tail offset before setting ring->tail

The HW only accepts offsets within ring->size, and fails peculiarly if
the RING_HEAD or RING_TAIL is set to ring->size. Therefore whenever we
set ring->head/ring->tail we want to make sure it is within value (using
intel_ring_wrap()).

v2: Double check execlists as well
v3: Remove redundancy with assert_ring_tail_valid()
v4: Just assert in intel_ring_reset() rather than be over-defensive.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> #v2
Link: https://patchwork.freedesktop.org/patch/msgid/20180611110845.31890-2-chris@chris-wilson.co.uk

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index d72a6a5ff3ac..bb4af8f84a22 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -496,6 +496,10 @@ static int init_ring_common(struct intel_engine_cs *engine)
 		DRM_DEBUG_DRIVER("%s initialization failed [head=%08x], fudging\n",
 				 engine->name, I915_READ_HEAD(engine));
 
+	/* Check that the ring offsets point within the ring! */
+	GEM_BUG_ON(!intel_ring_offset_valid(ring, ring->head));
+	GEM_BUG_ON(!intel_ring_offset_valid(ring, ring->tail));
+
 	intel_ring_update_space(ring);
 	I915_WRITE_HEAD(engine, ring->head);
 	I915_WRITE_TAIL(engine, ring->tail);
@@ -1062,6 +1066,8 @@ err:
 
 void intel_ring_reset(struct intel_ring *ring, u32 tail)
 {
+	GEM_BUG_ON(!intel_ring_offset_valid(ring, tail));
+
 	ring->tail = tail;
 	ring->head = tail;
 	ring->emit = tail;