[PATCH RFC v7 6/9] PM / devfreq: Add a governor for tracking remote device frequencies

[Pragnesh Papaniya]

From: Sibi Sankar <sibi.sankar at oss.qualcomm.com>

On SoCs where the governor and the mechanism to control the frequency
for devices like caches is hosted on the System Control Processor
(SCP), there exists a need to track the frequency changes in a
reliable way and provide ways to tweak parameters on the remote
governor.

Add a new "remote" devfreq governor that uses the track_remote
flag to expose the remote device's frequency to userspace via
trans_stat. The governor deliberately does not advertise the
DEVFREQ_GOV_ATTR_TARGET_FREQ attribute since the kernel cannot
set the frequency on a remote-managed device; reads of the
target_freq sysfs node therefore return -EINVAL.

Signed-off-by: Sibi Sankar <sibi.sankar at oss.qualcomm.com>
Signed-off-by: Pragnesh Papaniya <pragnesh.papaniya at oss.qualcomm.com>
---
 drivers/devfreq/Kconfig           |  8 +++++
 drivers/devfreq/Makefile          |  1 +
 drivers/devfreq/governor_remote.c | 73 +++++++++++++++++++++++++++++++++++++++
 include/linux/devfreq.h           |  1 +
 4 files changed, 83 insertions(+)

diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
index c999c4a1e567..2caa87554914 100644
--- a/drivers/devfreq/Kconfig
+++ b/drivers/devfreq/Kconfig
@@ -56,6 +56,14 @@ config DEVFREQ_GOV_POWERSAVE
 	  the DEVFREQ framework returns the lowest frequency available
 	  at any time.
 
+config DEVFREQ_GOV_REMOTE
+	tristate "Remote"
+	help
+	  A simple governor to track the frequency of devices whose
+	  dvfs control lies outside the kernel. This governor acts
+	  as an observer and provides for ways to track frequency and
+	  set/get information related to the remote dvfs device.
+
 config DEVFREQ_GOV_USERSPACE
 	tristate "Userspace"
 	help
diff --git a/drivers/devfreq/Makefile b/drivers/devfreq/Makefile
index 404179d79a9d..cde57c8cda76 100644
--- a/drivers/devfreq/Makefile
+++ b/drivers/devfreq/Makefile
@@ -4,6 +4,7 @@ obj-$(CONFIG_PM_DEVFREQ_EVENT)	+= devfreq-event.o
 obj-$(CONFIG_DEVFREQ_GOV_SIMPLE_ONDEMAND)	+= governor_simpleondemand.o
 obj-$(CONFIG_DEVFREQ_GOV_PERFORMANCE)	+= governor_performance.o
 obj-$(CONFIG_DEVFREQ_GOV_POWERSAVE)	+= governor_powersave.o
+obj-$(CONFIG_DEVFREQ_GOV_REMOTE)	+= governor_remote.o
 obj-$(CONFIG_DEVFREQ_GOV_USERSPACE)	+= governor_userspace.o
 obj-$(CONFIG_DEVFREQ_GOV_PASSIVE)	+= governor_passive.o
 
diff --git a/drivers/devfreq/governor_remote.c b/drivers/devfreq/governor_remote.c
new file mode 100644
index 000000000000..df3819757e56
--- /dev/null
+++ b/drivers/devfreq/governor_remote.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+ */
+
+#include <linux/errno.h>
+#include <linux/module.h>
+#include <linux/devfreq.h>
+#include <linux/devfreq-governor.h>
+
+static int devfreq_remote_track_func(struct devfreq *devfreq, unsigned long *freq)
+{
+	if (!devfreq->profile->get_cur_freq)
+		return -ENXIO;
+
+	return devfreq->profile->get_cur_freq(devfreq->dev.parent, freq);
+}
+
+static int devfreq_remote_track_handler(struct devfreq *devfreq, unsigned int event, void *data)
+{
+	switch (event) {
+	case DEVFREQ_GOV_START:
+		devfreq_monitor_start(devfreq);
+		break;
+
+	case DEVFREQ_GOV_STOP:
+		devfreq_monitor_stop(devfreq);
+		break;
+
+	case DEVFREQ_GOV_UPDATE_INTERVAL:
+		devfreq_update_interval(devfreq, (unsigned int *)data);
+		break;
+
+	case DEVFREQ_GOV_SUSPEND:
+		devfreq_monitor_suspend(devfreq);
+		break;
+
+	case DEVFREQ_GOV_RESUME:
+		devfreq_monitor_resume(devfreq);
+		break;
+	}
+
+	return 0;
+}
+
+static struct devfreq_governor devfreq_remote_track = {
+	.name = DEVFREQ_GOV_REMOTE,
+	.attrs = DEVFREQ_GOV_ATTR_POLLING_INTERVAL
+		| DEVFREQ_GOV_ATTR_TIMER,
+	.flags = DEVFREQ_GOV_FLAG_IMMUTABLE
+		| DEVFREQ_GOV_FLAG_TRACK_REMOTE,
+	.get_target_freq = devfreq_remote_track_func,
+	.event_handler = devfreq_remote_track_handler,
+};
+
+static int __init devfreq_remote_track_init(void)
+{
+	return devfreq_add_governor(&devfreq_remote_track);
+}
+subsys_initcall(devfreq_remote_track_init);
+
+static void __exit devfreq_remote_track_exit(void)
+{
+	int ret;
+
+	ret = devfreq_remove_governor(&devfreq_remote_track);
+	if (ret)
+		pr_err("%s: failed to remove governor %d\n", __func__, ret);
+}
+module_exit(devfreq_remote_track_exit);
+
+MODULE_DESCRIPTION("DEVFREQ Remote Tracking governor");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
index dc1075dc3446..4d50cf230950 100644
--- a/include/linux/devfreq.h
+++ b/include/linux/devfreq.h
@@ -21,6 +21,7 @@
 #define DEVFREQ_GOV_POWERSAVE		"powersave"
 #define DEVFREQ_GOV_USERSPACE		"userspace"
 #define DEVFREQ_GOV_PASSIVE		"passive"
+#define DEVFREQ_GOV_REMOTE		"remote"
 
 /* DEVFREQ notifier interface */
 #define DEVFREQ_TRANSITION_NOTIFIER	(0)

-- 
2.34.1