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

[Michel Thierry]

On 18/04/17 16:06, Chris Wilson wrote:
> 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.

Oh... proof that most of the time I only copy+paste stuff.

> -Chris
>