PM / devfreq: add support for suspend/resume of a devfreq device

The patch prepares devfreq device for handling suspend/resume
functionality. The new fields will store needed information during this
process. Devfreq framework handles opp-suspend DT entry and there is no
need of modyfications in the drivers code. It uses atomic variables to
make sure no race condition affects the process.

Suggested-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Suggested-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>

drivers/devfreq/devfreq.c

@@ -316,6 +316,10 @@ static int devfreq_set_target(struct devfreq *devfreq, unsigned long new_freq,
 			"Couldn't update frequency transition information.\n");
 
 	devfreq->previous_freq = new_freq;
+
+	if (devfreq->suspend_freq)
+		devfreq->resume_freq = cur_freq;
+
 	return err;
 }
 
@@ -667,6 +671,9 @@ struct devfreq *devfreq_add_device(struct device *dev,
 	}
 	devfreq->max_freq = devfreq->scaling_max_freq;
 
+	devfreq->suspend_freq = dev_pm_opp_get_suspend_opp_freq(dev);
+	atomic_set(&devfreq->suspend_count, 0);
+
 	dev_set_name(&devfreq->dev, "devfreq%d",
 				atomic_inc_return(&devfreq_no));
 	err = device_register(&devfreq->dev);
@@ -867,14 +874,28 @@ EXPORT_SYMBOL(devm_devfreq_remove_device);
  */
 int devfreq_suspend_device(struct devfreq *devfreq)
 {
+	int ret;
+
 	if (!devfreq)
 		return -EINVAL;
 
-	if (!devfreq->governor)
+	if (atomic_inc_return(&devfreq->suspend_count) > 1)
 		return 0;
 
-	return devfreq->governor->event_handler(devfreq,
+	if (devfreq->governor) {
+		ret = devfreq->governor->event_handler(devfreq,
 					DEVFREQ_GOV_SUSPEND, NULL);
+		if (ret)
+			return ret;
+	}
+
+	if (devfreq->suspend_freq) {
+		ret = devfreq_set_target(devfreq, devfreq->suspend_freq, 0);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
 }
 EXPORT_SYMBOL(devfreq_suspend_device);
 
@@ -888,14 +909,28 @@ EXPORT_SYMBOL(devfreq_suspend_device);
  */
 int devfreq_resume_device(struct devfreq *devfreq)
 {
+	int ret;
+
 	if (!devfreq)
 		return -EINVAL;
 
-	if (!devfreq->governor)
+	if (atomic_dec_return(&devfreq->suspend_count) >= 1)
 		return 0;
 
-	return devfreq->governor->event_handler(devfreq,
+	if (devfreq->resume_freq) {
+		ret = devfreq_set_target(devfreq, devfreq->resume_freq, 0);
+		if (ret)
+			return ret;
+	}
+
+	if (devfreq->governor) {
+		ret = devfreq->governor->event_handler(devfreq,
 					DEVFREQ_GOV_RESUME, NULL);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
 }
 EXPORT_SYMBOL(devfreq_resume_device);
 

include/linux/devfreq.h

@@ -131,6 +131,9 @@ struct devfreq_dev_profile {
  * @scaling_min_freq:	Limit minimum frequency requested by OPP interface
  * @scaling_max_freq:	Limit maximum frequency requested by OPP interface
  * @stop_polling:	 devfreq polling status of a device.
+ * @suspend_freq:	 frequency of a device set during suspend phase.
+ * @resume_freq:	 frequency of a device set in resume phase.
+ * @suspend_count:	 suspend requests counter for a device.
  * @total_trans:	Number of devfreq transitions
  * @trans_table:	Statistics of devfreq transitions
  * @time_in_state:	Statistics of devfreq states
@@ -167,6 +170,10 @@ struct devfreq {
 	unsigned long scaling_max_freq;
 	bool stop_polling;
 
+	unsigned long suspend_freq;
+	unsigned long resume_freq;
+	atomic_t suspend_count;
+
 	/* information for device frequency transition */
 	unsigned int total_trans;
 	unsigned int *trans_table;