[Intel-gfx] [PATCH] drm/i915: Configurable GT idle frequency

[Bob Paauwe]

There are real-time use cases where having deterministic CPU processes
can be more important than GPU power/performance. Parking the GPU at a
specific freqency by setting idle, min and max prohibits the normal
dynamic GPU frequency switching which can introduce significant PCI-E
latency. This adds the ability to configure the GPU "idle" frequecy
using the same method that already exists for minimum and maximum
frequencies.

In addition, parking the idle frequency may reduce spool up latencies
on GPU workloads.

Signed-off-by: Bob Paauwe <bob.j.paauwe at intel.com>
---
 drivers/gpu/drm/i915/i915_sysfs.c | 60 +++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_sysfs.c b/drivers/gpu/drm/i915/i915_sysfs.c
index 41313005af42..62612c23d514 100644
--- a/drivers/gpu/drm/i915/i915_sysfs.c
+++ b/drivers/gpu/drm/i915/i915_sysfs.c
@@ -454,11 +454,69 @@ static ssize_t gt_min_freq_mhz_store(struct device *kdev,
 	return ret ?: count;
 }
 
+static ssize_t gt_idle_freq_mhz_show(struct device *kdev, struct device_attribute *attr, char *buf)
+{
+	struct drm_i915_private *dev_priv = kdev_minor_to_i915(kdev);
+
+	return snprintf(buf, PAGE_SIZE, "%d\n",
+			intel_gpu_freq(dev_priv,
+				       dev_priv->gt_pm.rps.idle_freq));
+}
+
+static ssize_t gt_idle_freq_mhz_store(struct device *kdev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t count)
+{
+	struct drm_i915_private *dev_priv = kdev_minor_to_i915(kdev);
+	struct intel_rps *rps = &dev_priv->gt_pm.rps;
+	intel_wakeref_t wakeref;
+	u32 val;
+	ssize_t ret;
+
+	ret = kstrtou32(buf, 0, &val);
+	if (ret)
+		return ret;
+
+	wakeref = intel_runtime_pm_get(dev_priv);
+
+	mutex_lock(&dev_priv->pcu_lock);
+
+	val = intel_freq_opcode(dev_priv, val);
+
+	if (val < rps->min_freq ||
+	    val > rps->max_freq ||
+	    val > rps->max_freq_softlimit) {
+		mutex_unlock(&dev_priv->pcu_lock);
+		intel_runtime_pm_put(dev_priv, wakeref);
+		return -EINVAL;
+	}
+
+	rps->idle_freq = val;
+
+	val = clamp_t(int, rps->cur_freq,
+		      rps->idle_freq,
+		      rps->max_freq_softlimit);
+
+	/*
+	 * If the current freq is at the old idle freq we should
+	 * ajust it to the new idle.  Calling *_set_rps will also
+	 * update the interrupt limits and PMINTRMSK if ncessary.
+	 */
+	ret = intel_set_rps(dev_priv, val);
+
+	mutex_unlock(&dev_priv->pcu_lock);
+
+	intel_runtime_pm_put(dev_priv, wakeref);
+
+	return ret ?: count;
+}
+
 static DEVICE_ATTR_RO(gt_act_freq_mhz);
 static DEVICE_ATTR_RO(gt_cur_freq_mhz);
 static DEVICE_ATTR_RW(gt_boost_freq_mhz);
 static DEVICE_ATTR_RW(gt_max_freq_mhz);
 static DEVICE_ATTR_RW(gt_min_freq_mhz);
+static DEVICE_ATTR_RW(gt_idle_freq_mhz);
 
 static DEVICE_ATTR_RO(vlv_rpe_freq_mhz);
 
@@ -492,6 +550,7 @@ static const struct attribute * const gen6_attrs[] = {
 	&dev_attr_gt_boost_freq_mhz.attr,
 	&dev_attr_gt_max_freq_mhz.attr,
 	&dev_attr_gt_min_freq_mhz.attr,
+	&dev_attr_gt_idle_freq_mhz.attr,
 	&dev_attr_gt_RP0_freq_mhz.attr,
 	&dev_attr_gt_RP1_freq_mhz.attr,
 	&dev_attr_gt_RPn_freq_mhz.attr,
@@ -504,6 +563,7 @@ static const struct attribute * const vlv_attrs[] = {
 	&dev_attr_gt_boost_freq_mhz.attr,
 	&dev_attr_gt_max_freq_mhz.attr,
 	&dev_attr_gt_min_freq_mhz.attr,
+	&dev_attr_gt_idle_freq_mhz.attr,
 	&dev_attr_gt_RP0_freq_mhz.attr,
 	&dev_attr_gt_RP1_freq_mhz.attr,
 	&dev_attr_gt_RPn_freq_mhz.attr,
-- 
2.19.2