drm/panfrost: use spinlock instead of atomic

Convert busy_count to a simple int protected by spinlock.

Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Signed-off-by: Clément Péron <peron.clem@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200710095409.407087-6-peron.clem@gmail.com

drivers/gpu/drm/panfrost/panfrost_devfreq.c

@@ -12,16 +12,12 @@
 
 static void panfrost_devfreq_update_utilization(struct panfrost_devfreq *pfdevfreq)
 {
-	ktime_t now;
+	ktime_t now, last;
-	ktime_t last;
-
-	if (!pfdevfreq->devfreq)
-		return;
 
 	now = ktime_get();
 	last = pfdevfreq->time_last_update;
 
-	if (atomic_read(&pfdevfreq->busy_count) > 0)
+	if (pfdevfreq->busy_count > 0)
 		pfdevfreq->busy_time += ktime_sub(now, last);
 	else
 		pfdevfreq->idle_time += ktime_sub(now, last);
@@ -59,10 +55,14 @@ static int panfrost_devfreq_get_dev_status(struct device *dev,
 {
 	struct panfrost_device *pfdev = dev_get_drvdata(dev);
 	struct panfrost_devfreq *pfdevfreq = &pfdev->pfdevfreq;
+	unsigned long irqflags;
+
+	status->current_frequency = clk_get_rate(pfdev->clock);
+
+	spin_lock_irqsave(&pfdevfreq->lock, irqflags);
 
 	panfrost_devfreq_update_utilization(pfdevfreq);
 
-	status->current_frequency = clk_get_rate(pfdev->clock);
 	status->total_time = ktime_to_ns(ktime_add(pfdevfreq->busy_time,
 						   pfdevfreq->idle_time));
 
@@ -70,6 +70,8 @@ static int panfrost_devfreq_get_dev_status(struct device *dev,
 
 	panfrost_devfreq_reset(pfdevfreq);
 
+	spin_unlock_irqrestore(&pfdevfreq->lock, irqflags);
+
 	dev_dbg(pfdev->dev, "busy %lu total %lu %lu %% freq %lu MHz\n",
 		status->busy_time, status->total_time,
 		status->busy_time / (status->total_time / 100),
@@ -100,6 +102,8 @@ int panfrost_devfreq_init(struct panfrost_device *pfdev)
 	else if (ret)
 		return ret;
 
+	spin_lock_init(&pfdevfreq->lock);
+
 	panfrost_devfreq_reset(pfdevfreq);
 
 	cur_freq = clk_get_rate(pfdev->clock);
@@ -162,15 +166,32 @@ void panfrost_devfreq_suspend(struct panfrost_device *pfdev)
 
 void panfrost_devfreq_record_busy(struct panfrost_devfreq *pfdevfreq)
 {
+	unsigned long irqflags;
+
+	if (!pfdevfreq->devfreq)
+		return;
+
+	spin_lock_irqsave(&pfdevfreq->lock, irqflags);
+
 	panfrost_devfreq_update_utilization(pfdevfreq);
-	atomic_inc(&pfdevfreq->busy_count);
+
+	pfdevfreq->busy_count++;
+
+	spin_unlock_irqrestore(&pfdevfreq->lock, irqflags);
 }
 
 void panfrost_devfreq_record_idle(struct panfrost_devfreq *pfdevfreq)
 {
-	int count;
+	unsigned long irqflags;
+
+	if (!pfdevfreq->devfreq)
+		return;
+
+	spin_lock_irqsave(&pfdevfreq->lock, irqflags);
 
 	panfrost_devfreq_update_utilization(pfdevfreq);
-	count = atomic_dec_if_positive(&pfdevfreq->busy_count);
+
-	WARN_ON(count < 0);
+	WARN_ON(--pfdevfreq->busy_count < 0);
+
+	spin_unlock_irqrestore(&pfdevfreq->lock, irqflags);
 }

drivers/gpu/drm/panfrost/panfrost_devfreq.h

@@ -4,6 +4,7 @@
 #ifndef __PANFROST_DEVFREQ_H__
 #define __PANFROST_DEVFREQ_H__
 
+#include <linux/spinlock.h>
 #include <linux/ktime.h>
 
 struct devfreq;
@@ -14,10 +15,16 @@ struct panfrost_device;
 struct panfrost_devfreq {
 	struct devfreq *devfreq;
 	struct thermal_cooling_device *cooling;
+
 	ktime_t busy_time;
 	ktime_t idle_time;
 	ktime_t time_last_update;
-	atomic_t busy_count;
+	int busy_count;
+	/*
+	 * Protect busy_time, idle_time, time_last_update and busy_count
+	 * because these can be updated concurrently between multiple jobs.
+	 */
+	spinlock_t lock;
 };
 
 int panfrost_devfreq_init(struct panfrost_device *pfdev);