drm/i915/selftest: Add throttle reason diagnostics to RPS selftests

Report GPU throttle reasons when RPS tests fail to reach expected
frequencies or power levels.

v2: Read the throttle value before the spinner ends (Raag)
    Add a condition before printing throttle value (Krzysztof)
v3: Extend throttle reasons debug support (Raag)
v4: Cosmetic changes (Raag)

Signed-off-by: Sk Anirban <sk.anirban@intel.com>
Reviewed-by: Raag Jadav <raag.jadav@intel.com>
Reviewed-by: Krzysztof Karas <krzysztof.karas@intel.com>
Link: https://patch.msgid.link/20251223101605.3304379-2-sk.anirban@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>

Author: sanirban-999

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

@@ -378,6 +378,7 @@ int live_rps_control(void *arg)
 	enum intel_engine_id id;
 	struct igt_spinner spin;
 	intel_wakeref_t wakeref;
+	u32 throttle;
 	int err = 0;
 
 	/*
@@ -463,6 +464,9 @@ int live_rps_control(void *arg)
 		max = rps_set_check(rps, limit);
 		max_dt = ktime_sub(ktime_get(), max_dt);
 
+		throttle = intel_uncore_read(gt->uncore, intel_gt_perf_limit_reasons_reg(gt));
+		throttle &= GT0_PERF_LIMIT_REASONS_MASK;
+
 		min_dt = ktime_get();
 		min = rps_set_check(rps, rps->min_freq);
 		min_dt = ktime_sub(ktime_get(), min_dt);
@@ -478,11 +482,9 @@ int live_rps_control(void *arg)
 			min, max, ktime_to_ns(min_dt), ktime_to_ns(max_dt));
 
 		if (limit != rps->max_freq) {
-			u32 throttle = intel_uncore_read(gt->uncore,
-							 intel_gt_perf_limit_reasons_reg(gt));
-
-			pr_warn("%s: GPU throttled with reasons 0x%08x\n",
-				engine->name, throttle & GT0_PERF_LIMIT_REASONS_MASK);
+			if (throttle)
+				pr_warn("%s: GPU throttled with reasons 0x%08x\n",
+					engine->name, throttle);
 			show_pstate_limits(rps);
 		}
 
@@ -1138,6 +1140,7 @@ int live_rps_power(void *arg)
 	struct intel_engine_cs *engine;
 	enum intel_engine_id id;
 	struct igt_spinner spin;
+	u32 throttle;
 	int err = 0;
 
 	/*
@@ -1195,6 +1198,9 @@ int live_rps_power(void *arg)
 		max.freq = rps->max_freq;
 		max.power = measure_power_at(rps, &max.freq);
 
+		throttle = intel_uncore_read(gt->uncore, intel_gt_perf_limit_reasons_reg(gt));
+		throttle &= GT0_PERF_LIMIT_REASONS_MASK;
+
 		min.freq = rps->min_freq;
 		min.power = measure_power_at(rps, &min.freq);
 
@@ -1210,12 +1216,21 @@ int live_rps_power(void *arg)
 			pr_notice("Could not control frequency, ran at [%d:%uMHz, %d:%uMhz]\n",
 				  min.freq, intel_gpu_freq(rps, min.freq),
 				  max.freq, intel_gpu_freq(rps, max.freq));
+
+			if (throttle)
+				pr_warn("%s: GPU throttled with reasons 0x%08x\n",
+					engine->name, throttle);
 			continue;
 		}
 
 		if (11 * min.power > 10 * max.power) {
 			pr_err("%s: did not conserve power when setting lower frequency!\n",
 			       engine->name);
+
+			if (throttle)
+				pr_warn("%s: GPU throttled with reasons 0x%08x\n",
+					engine->name, throttle);
+
 			err = -EINVAL;
 			break;
 		}
@@ -1241,6 +1256,7 @@ int live_rps_dynamic(void *arg)
 	struct intel_engine_cs *engine;
 	enum intel_engine_id id;
 	struct igt_spinner spin;
+	u32 throttle;
 	int err = 0;
 
 	/*
@@ -1293,6 +1309,9 @@ int live_rps_dynamic(void *arg)
 		max.freq = wait_for_freq(rps, rps->max_freq, 500);
 		max.dt = ktime_sub(ktime_get(), max.dt);
 
+		throttle = intel_uncore_read(gt->uncore, intel_gt_perf_limit_reasons_reg(gt));
+		throttle &= GT0_PERF_LIMIT_REASONS_MASK;
+
 		igt_spinner_end(&spin);
 
 		min.dt = ktime_get();
@@ -1308,6 +1327,11 @@ int live_rps_dynamic(void *arg)
 		if (min.freq >= max.freq) {
 			pr_err("%s: dynamic reclocking of spinner failed\n!",
 			       engine->name);
+
+			if (throttle)
+				pr_warn("%s: GPU throttled with reasons 0x%08x\n",
+					engine->name, throttle);
+
 			err = -EINVAL;
 		}