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

[Chris Wilson]

On Tue, Apr 18, 2017 at 02:36:14PM -0700, Michel Thierry wrote:
> 
> 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.

Yes, we shouldn't be setting the watchdog threshold if the watchdog is
not available. GEM_BUG_ON() would be fine. Throwing a very, very late
EINVAL is disconcerting.
 
> 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.

Seems reasonable.

> >>+
> >>+		/* + 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.

LRI(2), but only setting one register not two.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre