Re: [PATCH v6 17/20] drm/i915: Watchdog timeout: Ringbuffer command emission for gen8+

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On 18/04/17 14:20, Chris Wilson wrote:
On Tue, Apr 18, 2017 at 01:23:32PM -0700, Michel Thierry wrote:
@@ -1329,10 +1331,29 @@ static int gen8_emit_bb_start(struct drm_i915_gem_request *req,
 		req->ctx->ppgtt->pd_dirty_rings &= ~intel_engine_flag(req->engine);
 	}

-	cs = intel_ring_begin(req, 4);
+	/* bb_start only */
+	num_dwords = 4;
+
+	/* check if watchdog will be required */
+	if (req->ctx->engine[req->engine->id].watchdog_threshold != 0) {
+		if (!req->engine->emit_start_watchdog ||
+		    !req->engine->emit_stop_watchdog)
+			return -EINVAL;

This is still a bug in the context setparam to get to this point without
a watchdog.


This can't happen (threshold != 0 && no emit_watchdog func), i915_gem_context_set_watchdog returns -ENODEV if vcs's emit_start_watchdog is not defined (the assumption is if the vcs has it, rcs does too).

I can remove it, if that's what you mean.

But re i915_gem_context_set_watchdog, I think maybe it should return ENODEV when there's no watchdog and the user is trying to get the array size (args->size == 0), and don't give false hopes.

+
+		/* + start_watchdog (6) + stop_watchdog (4) */
+		num_dwords += 10;
+		watchdog_running = true;
+	}
+static u32 *gen8_emit_stop_watchdog(struct drm_i915_gem_request *req, u32 *cs)
+{
+	struct intel_engine_cs *engine = req->engine;
+
+	/* XXX: no watchdog support in BCS engine */
+	GEM_BUG_ON(engine->id == BCS);
+
+	*cs++ = MI_LOAD_REGISTER_IMM(2);
+	*cs++ = i915_mmio_reg_offset(RING_CNTR(engine->mmio_base));
+	*cs++ = get_watchdog_disable(engine);
+	*cs++ = MI_NOOP;

Oops.

_context_set_watchdog also rejects if threshold[BCS] != 0.

-Chris

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