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: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Thomas Daniel <thomas.daniel@intel.com>
Signed-off-by: Michel Thierry <michel.thierry@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index d07c0b1..53394f9 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2377,10 +2377,11 @@
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
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index fcb074b..09df74b 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -393,6 +393,26 @@
}
}
+ 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 @@
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 @@
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;
}