drm/i915: correctly order the ring init sequence
We may only start to set up the new register values after having
confirmed that the ring is truely off. Otherwise the hw might lose the
newly written register values. This is caught later on in the init
sequence, when we check whether the register writes have stuck.
Cc: stable@vger.kernel.org
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50522
Tested-by: Yang Guang <guang.a.yang@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index bf0195a..414af1e 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -289,8 +289,6 @@
I915_WRITE_HEAD(ring, 0);
ring->write_tail(ring, 0);
- /* Initialize the ring. */
- I915_WRITE_START(ring, obj->gtt_offset);
head = I915_READ_HEAD(ring) & HEAD_ADDR;
/* G45 ring initialization fails to reset head to zero */
@@ -316,6 +314,11 @@
}
}
+ /* Initialize the ring. This must happen _after_ we've cleared the ring
+ * registers with the above sequence (the readback of the HEAD registers
+ * also enforces ordering), otherwise the hw might lose the new ring
+ * register values. */
+ I915_WRITE_START(ring, obj->gtt_offset);
I915_WRITE_CTL(ring,
((ring->size - PAGE_SIZE) & RING_NR_PAGES)
| RING_VALID);