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drm/i915: Workaround to avoid lite restore with HEAD==TAIL

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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>
This commit is contained in:
Michel Thierry 2015-04-15 18:11:33 +01:00 committed by Jani Nikula
parent 9535c4757b
commit 53292cdb06
2 changed files with 36 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
drivers/gpu/drm/i915/i915_gem.c
View File

@ -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

35
drivers/gpu/drm/i915/intel_lrc.c
View File

@ -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;
}