From: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Date: Tue, 20 Mar 2018 17:17:33 +0200
Subject: drm/i915: Avoid setting ring freq on invalid rps freqs
Git-commit: 66c1f77ae2b773f349c1ea1312d69a6ab775cc26
Patch-mainline: v4.18-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

Looping through rps frequencies when both min and max are zero
ends up into an endless loop. This can happen during hardware
enablement.

Bail out early if rps frequencies are not correctly set yet.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180320151734.11761-1-mika.kuoppala@linux.intel.com

Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/i915/intel_pm.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -6890,15 +6890,18 @@ static void gen6_enable_rps(struct drm_i
 static void gen6_update_ring_freq(struct drm_i915_private *dev_priv)
 {
 	struct intel_rps *rps = &dev_priv->gt_pm.rps;
-	int min_freq = 15;
+	const int min_freq = 15;
+	const int scaling_factor = 180;
 	unsigned int gpu_freq;
 	unsigned int max_ia_freq, min_ring_freq;
 	unsigned int max_gpu_freq, min_gpu_freq;
-	int scaling_factor = 180;
 	struct cpufreq_policy *policy;
 
 	WARN_ON(!mutex_is_locked(&dev_priv->pcu_lock));
 
+	if (rps->max_freq <= rps->min_freq)
+		return;
+
 	policy = cpufreq_cpu_get(0);
 	if (policy) {
 		max_ia_freq = policy->cpuinfo.max_freq;
@@ -6932,7 +6935,7 @@ static void gen6_update_ring_freq(struct
 	 * the PCU should use as a reference to determine the ring frequency.
 	 */
 	for (gpu_freq = max_gpu_freq; gpu_freq >= min_gpu_freq; gpu_freq--) {
-		int diff = max_gpu_freq - gpu_freq;
+		const int diff = max_gpu_freq - gpu_freq;
 		unsigned int ia_freq = 0, ring_freq = 0;
 
 		if (IS_GEN9_BC(dev_priv) || IS_CANNONLAKE(dev_priv)) {