drm/i915/guc/slpc: Add SLPC selftest live_slpc_power

A fundamental assumption is that at lower frequencies,
not only do we run slower, but we save power compared to
higher frequencies.
live_slpc_power checks if running at low frequency saves power

v2: re-use code to measure power
    fixed cosmetic review comments (Vinay)
Signed-off-by: Riana Tauro <riana.tauro@intel.com>
Reviewed-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220923110043.789178-4-riana.tauro@intel.com

drivers/gpu/drm/i915/gt/selftest_slpc.c

@@ -11,7 +11,8 @@
 enum test_type {
 	VARY_MIN,
 	VARY_MAX,
-	MAX_GRANTED
+	MAX_GRANTED,
+	SLPC_POWER,
 };
 
 static int slpc_set_min_freq(struct intel_guc_slpc *slpc, u32 freq)
@@ -41,6 +42,39 @@ static int slpc_set_max_freq(struct intel_guc_slpc *slpc, u32 freq)
 	return ret;
 }
 
+static int slpc_set_freq(struct intel_gt *gt, u32 freq)
+{
+	int err;
+	struct intel_guc_slpc *slpc = &gt->uc.guc.slpc;
+
+	err = slpc_set_max_freq(slpc, freq);
+	if (err) {
+		pr_err("Unable to update max freq");
+		return err;
+	}
+
+	err = slpc_set_min_freq(slpc, freq);
+	if (err) {
+		pr_err("Unable to update min freq");
+		return err;
+	}
+
+	return err;
+}
+
+static u64 measure_power_at_freq(struct intel_gt *gt, int *freq, u64 *power)
+{
+	int err = 0;
+
+	err = slpc_set_freq(gt, *freq);
+	if (err)
+		return err;
+	*freq = intel_rps_read_actual_frequency(&gt->rps);
+	*power = measure_power(&gt->rps, freq);
+
+	return err;
+}
+
 static int vary_max_freq(struct intel_guc_slpc *slpc, struct intel_rps *rps,
 			 u32 *max_act_freq)
 {
@@ -113,6 +147,58 @@ static int vary_min_freq(struct intel_guc_slpc *slpc, struct intel_rps *rps,
 	return err;
 }
 
+static int slpc_power(struct intel_gt *gt, struct intel_engine_cs *engine)
+{
+	struct intel_guc_slpc *slpc = &gt->uc.guc.slpc;
+	struct {
+		u64 power;
+		int freq;
+	} min, max;
+	int err = 0;
+
+	/*
+	 * Our fundamental assumption is that running at lower frequency
+	 * actually saves power. Let's see if our RAPL measurement supports
+	 * that theory.
+	 */
+	if (!librapl_supported(gt->i915))
+		return 0;
+
+	min.freq = slpc->min_freq;
+	err = measure_power_at_freq(gt, &min.freq, &min.power);
+
+	if (err)
+		return err;
+
+	max.freq = slpc->rp0_freq;
+	err = measure_power_at_freq(gt, &max.freq, &max.power);
+
+	if (err)
+		return err;
+
+	pr_info("%s: min:%llumW @ %uMHz, max:%llumW @ %uMHz\n",
+		engine->name,
+		min.power, min.freq,
+		max.power, max.freq);
+
+	if (10 * min.freq >= 9 * max.freq) {
+		pr_notice("Could not control frequency, ran at [%uMHz, %uMhz]\n",
+			  min.freq, max.freq);
+	}
+
+	if (11 * min.power > 10 * max.power) {
+		pr_err("%s: did not conserve power when setting lower frequency!\n",
+		       engine->name);
+		err = -EINVAL;
+	}
+
+	/* Restore min/max frequencies */
+	slpc_set_max_freq(slpc, slpc->rp0_freq);
+	slpc_set_min_freq(slpc, slpc->min_freq);
+
+	return err;
+}
+
 static int max_granted_freq(struct intel_guc_slpc *slpc, struct intel_rps *rps, u32 *max_act_freq)
 {
 	struct intel_gt *gt = rps_to_gt(rps);
@@ -233,8 +319,13 @@ static int run_test(struct intel_gt *gt, int test_type)
 
 			err = max_granted_freq(slpc, rps, &max_act_freq);
 			break;
+
+		case SLPC_POWER:
+			err = slpc_power(gt, engine);
+			break;
 		}
 
+		if (test_type != SLPC_POWER) {
 			pr_info("Max actual frequency for %s was %d\n",
 				engine->name, max_act_freq);
 
@@ -245,6 +336,7 @@ static int run_test(struct intel_gt *gt, int test_type)
 				       intel_uncore_read(gt->uncore, GT0_PERF_LIMIT_REASONS));
 				err = -EINVAL;
 			}
+		}
 
 		igt_spinner_end(&spin);
 		st_engine_heartbeat_enable(engine);
@@ -316,12 +408,29 @@ static int live_slpc_max_granted(void *arg)
 	return ret;
 }
 
+static int live_slpc_power(void *arg)
+{
+	struct drm_i915_private *i915 = arg;
+	struct intel_gt *gt;
+	unsigned int i;
+	int ret;
+
+	for_each_gt(gt, i915, i) {
+		ret = run_test(gt, SLPC_POWER);
+		if (ret)
+			return ret;
+	}
+
+	return ret;
+}
+
 int intel_slpc_live_selftests(struct drm_i915_private *i915)
 {
 	static const struct i915_subtest tests[] = {
 		SUBTEST(live_slpc_vary_max),
 		SUBTEST(live_slpc_vary_min),
 		SUBTEST(live_slpc_max_granted),
+		SUBTEST(live_slpc_power),
 	};
 
 	struct intel_gt *gt;