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Commit 53292cdb authored by Michel Thierry's avatar Michel Thierry Committed by Jani Nikula
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drm/i915: Workaround to avoid lite restore with HEAD==TAIL 



WaIdleLiteRestore is an execlists-only workaround, and requires the driver
to ensure that any context always has HEAD!=TAIL when attempting lite
restore.

Add two extra MI_NOOP instructions at the end of each request, but keep
the requests tail pointing before the MI_NOOPs. We may not need to
executed them, and this is why request->tail is sampled before adding
these extra instructions.

If we submit a context to the ELSP which has previously been submitted,
move the tail pointer past the MI_NOOPs. This ensures HEAD!=TAIL.

v2: Move overallocation to gen8_emit_request, and added note about
sampling request->tail in commit message (Chris).

v3: Remove redundant request->tail assignment in __i915_add_request, in
lrc mode this is already set in execlists_context_queue.
Do not add wa implementation details inside gem (Chris).

v4: Apply the wa whenever the req has been resubmitted and update
comment (Chris).

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: default avatarThomas Daniel <thomas.daniel@intel.com>
Signed-off-by: default avatarMichel Thierry <michel.thierry@intel.com>
Signed-off-by: default avatarJani Nikula <jani.nikula@intel.com>
parent 9535c475

drivers/gpu/drm/i915/i915_gem.c

+2 −1
Original line number Diff line number Diff line
@@ -2377,10 +2377,11 @@ int __i915_add_request(struct intel_engine_cs *ring, 
		ret = ring->add_request(ring);

		if (ret)

			return ret;



		request->tail = intel_ring_get_tail(ringbuf);

	}



	request->head = request_start;

	request->tail = intel_ring_get_tail(ringbuf);



	/* Whilst this request exists, batch_obj will be on the

	 * active_list, and so will hold the active reference. Only when this

drivers/gpu/drm/i915/intel_lrc.c

+34 −1
Original line number Diff line number Diff line
@@ -393,6 +393,26 @@ static void execlists_context_unqueue(struct intel_engine_cs *ring) 
		}

	}



	if (IS_GEN8(ring->dev) || IS_GEN9(ring->dev)) {

		/*

		 * WaIdleLiteRestore: make sure we never cause a lite

		 * restore with HEAD==TAIL

		 */

		if (req0 && req0->elsp_submitted) {

			/*

			 * Apply the wa NOOPS to prevent ring:HEAD == req:TAIL

			 * as we resubmit the request. See gen8_emit_request()

			 * for where we prepare the padding after the end of the

			 * request.

			 */

			struct intel_ringbuffer *ringbuf;



			ringbuf = req0->ctx->engine[ring->id].ringbuf;

			req0->tail += 8;

			req0->tail &= ringbuf->size - 1;

		}

	}



	WARN_ON(req1 && req1->elsp_submitted);



	execlists_submit_contexts(ring, req0->ctx, req0->tail,
@@ -1315,7 +1335,12 @@ static int gen8_emit_request(struct intel_ringbuffer *ringbuf, 
	u32 cmd;

	int ret;



	ret = intel_logical_ring_begin(ringbuf, request->ctx, 6);

	/*

	 * Reserve space for 2 NOOPs at the end of each request to be

	 * used as a workaround for not being allowed to do lite

	 * restore with HEAD==TAIL (WaIdleLiteRestore).

	 */

	ret = intel_logical_ring_begin(ringbuf, request->ctx, 8);

	if (ret)

		return ret;
@@ -1333,6 +1358,14 @@ static int gen8_emit_request(struct intel_ringbuffer *ringbuf, 
	intel_logical_ring_emit(ringbuf, MI_NOOP);

	intel_logical_ring_advance_and_submit(ringbuf, request->ctx, request);



	/*

	 * Here we add two extra NOOPs as padding to avoid

	 * lite restore of a context with HEAD==TAIL.

	 */

	intel_logical_ring_emit(ringbuf, MI_NOOP);

	intel_logical_ring_emit(ringbuf, MI_NOOP);

	intel_logical_ring_advance(ringbuf);



	return 0;

}