[PATCH 5/9] drm/i915: Enable i915 perf stream for Haswell OA unit

[Chris Wilson]

On Wed, Apr 20, 2016 at 03:23:10PM +0100, Robert Bragg wrote:
> +static void i915_oa_stream_enable(struct i915_perf_stream *stream)
> +{
> +	struct drm_i915_private *dev_priv = stream->dev_priv;
> +
> +	dev_priv->perf.oa.ops.oa_enable(dev_priv);
> +
> +	if (dev_priv->perf.oa.periodic)
> +		hrtimer_start(&dev_priv->perf.oa.poll_check_timer,
> +			      ns_to_ktime(POLL_PERIOD),
> +			      HRTIMER_MODE_REL_PINNED);
> +}

> +static void i915_oa_stream_disable(struct i915_perf_stream *stream)
> +{
> +	struct drm_i915_private *dev_priv = stream->dev_priv;
> +
> +	dev_priv->perf.oa.ops.oa_disable(dev_priv);
> +
> +	if (dev_priv->perf.oa.periodic)
> +		hrtimer_cancel(&dev_priv->perf.oa.poll_check_timer);
> +}

> +static enum hrtimer_restart oa_poll_check_timer_cb(struct hrtimer *hrtimer)
> +{
> +	struct drm_i915_private *dev_priv =
> +		container_of(hrtimer, typeof(*dev_priv),
> +			     perf.oa.poll_check_timer);
> +
> +	if (!dev_priv->perf.oa.ops.oa_buffer_is_empty(dev_priv))
> +		wake_up(&dev_priv->perf.oa.poll_wq);
> +
> +	hrtimer_forward_now(hrtimer, ns_to_ktime(POLL_PERIOD));
> +
> +	return HRTIMER_RESTART;
> +}

> @@ -424,8 +1313,37 @@ void i915_perf_init(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(dev);
>  
> +	if (!IS_HASWELL(dev))
> +		return;
> +
> +	hrtimer_init(&dev_priv->perf.oa.poll_check_timer,
> +		     CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> +	dev_priv->perf.oa.poll_check_timer.function = oa_poll_check_timer_cb;
> +	init_waitqueue_head(&dev_priv->perf.oa.poll_wq);

This timer only serves to wake up pollers / wait_unlocked, right? So why
is it always running (when the stream is enabled)?

What happens to poll / wait_unlocked if oa.periodic is not set? It seems
like those functions would block indefinitely.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre