[PATCH] drm/i915/gt: Disable arbitration around Braswell's pdp updates

[Chris Wilson]

Braswell's pdp workaround is full of dragons, that may be being angered
when they are interrupted. Let's not take that risk and disable
arbitrartion during the update.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_execlists_submission.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
index 52c1fe62bdfe..10e9940cf3f5 100644
--- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
+++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
@@ -2539,6 +2539,14 @@ static int emit_pdps(struct i915_request *rq)
 	 * GPU hangs to forcewake errors and machine lockups!
 	 */
 
+	cs = intel_ring_begin(rq, 2);
+	if (IS_ERR(cs))
+		return PTR_ERR(cs);
+
+	*cs++ = MI_ARB_ON_OFF | MI_ARB_DISABLE;
+	*cs++ = MI_NOOP;
+	intel_ring_advance(rq, cs);
+
 	/* Flush any residual operations from the context load */
 	err = engine->emit_flush(rq, EMIT_FLUSH);
 	if (err)
@@ -2564,7 +2572,8 @@ static int emit_pdps(struct i915_request *rq)
 		*cs++ = i915_mmio_reg_offset(GEN8_RING_PDP_LDW(base, i));
 		*cs++ = lower_32_bits(pd_daddr);
 	}
-	*cs++ = MI_NOOP;
+	*cs++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
+	intel_ring_advance(rq, cs);
 
 	intel_ring_advance(rq, cs);
 
-- 
2.20.1