Re: [Intel-gfx] [PATCH 3/4] drm/i915/gt: Always send a pulse down the engine after disabling heartbeat

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 16/09/2020 10:42, Chris Wilson wrote:
> Currently, we check we can send a pulse prior to disabling the
> heartbeat to verify that we can change the heartbeat, but since we may
> re-evaluate execution upon changing the heartbeat interval we need another
> pulse afterwards to refresh execution.
> 
> Fixes: 9a40bddd47ca ("drm/i915/gt: Expose heartbeat interval via sysfs")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: <stable@vger.kernel.org> # v5.7+
> ---
>   drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c b/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c
> index 8ffdf676c0a0..d09df370f7cd 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c
> @@ -192,10 +192,12 @@ int intel_engine_set_heartbeat(struct intel_engine_cs *engine,
>   	WRITE_ONCE(engine->props.heartbeat_interval_ms, delay);
>   
>   	if (intel_engine_pm_get_if_awake(engine)) {
> -		if (delay)
> +		if (delay) {
>   			intel_engine_unpark_heartbeat(engine);
> -		else
> +		} else {
>   			intel_engine_park_heartbeat(engine);
> +			intel_engine_pulse(engine); /* recheck execution */
> +		}
>   		intel_engine_pm_put(engine);
>   	}
>   
> 

I did not immediately get this one. Do we really need two pulses or 
maybe we could re-order the code a bit and just undo the heartbeat park 
if pulse after parking did not work?

Regards,

Tvrtko
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