[PATCH v4 11/12] misc: throttler: Add Chrome OS EC throttler

[Matthias Kaehlcke]

The driver subscribes to throttling events from the Chrome OS
embedded controller and enables/disables system throttling based
on these events.

Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
Reviewed-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
Reviewed-by: Brian Norris <briannorris@xxxxxxxxxxxx>
---
Changes in v4:
- adapt to parent being struct cros_ec_dev instead of struct
  cros_ec_device
- added 'Reviewed-by: Brian Norris <briannorris@xxxxxxxxxxxx>' tag

Changes in v3:
- change module license to GPL v2 as in the SPDX identifier
- don't instantiate the throttler through the DT (instantiation
  by CrOS EC MFD in a separate patch)

Changes in v2:
- added SPDX line instead of license boiler-plate
- use macro to avoid splitting line
- changed variable name for throttler from 'cte' to 'ce_thr'
- formatting fixes
- Kconfig: removed odd dashes around 'help'
- added 'Reviewed-by' tag
---
 drivers/misc/throttler/Kconfig             |  10 ++
 drivers/misc/throttler/Makefile            |   1 +
 drivers/misc/throttler/cros_ec_throttler.c | 111 +++++++++++++++++++++
 3 files changed, 122 insertions(+)
 create mode 100644 drivers/misc/throttler/cros_ec_throttler.c

diff --git a/drivers/misc/throttler/Kconfig b/drivers/misc/throttler/Kconfig
index 8b2e63b2ef48..ef984c96f67b 100644
--- a/drivers/misc/throttler/Kconfig
+++ b/drivers/misc/throttler/Kconfig
@@ -20,4 +20,14 @@ menuconfig THROTTLER_DEBUG
 
 	  Choose N unless you want to debug throttler drivers.
 
+config CROS_EC_THROTTLER
+	tristate "Throttler event monitor for the Chrome OS Embedded Controller"
+	depends on MFD_CROS_EC
+	help
+	  This driver adds support to throttle the system in reaction to
+	  Chrome OS EC events.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called cros_ec_throttler.
+
 endif # THROTTLER
diff --git a/drivers/misc/throttler/Makefile b/drivers/misc/throttler/Makefile
index c8d920cee315..d9b2a77dabc9 100644
--- a/drivers/misc/throttler/Makefile
+++ b/drivers/misc/throttler/Makefile
@@ -1 +1,2 @@
 obj-$(CONFIG_THROTTLER)		+= core.o
+obj-$(CONFIG_CROS_EC_THROTTLER)	+= cros_ec_throttler.o
diff --git a/drivers/misc/throttler/cros_ec_throttler.c b/drivers/misc/throttler/cros_ec_throttler.c
new file mode 100644
index 000000000000..82a25415a264
--- /dev/null
+++ b/drivers/misc/throttler/cros_ec_throttler.c
@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for throttling triggered by events from the Chrome OS Embedded
+ * Controller.
+ *
+ * Copyright (C) 2018 Google, Inc.
+ */
+
+#include <linux/kernel.h>
+#include <linux/mfd/cros_ec.h>
+#include <linux/module.h>
+#include <linux/notifier.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/throttler.h>
+
+#define nb_to_ce_thr(nb) container_of(nb, struct cros_ec_throttler, nb)
+
+struct cros_ec_throttler {
+	struct cros_ec_device *ec;
+	struct throttler *throttler;
+	struct notifier_block nb;
+};
+
+static int cros_ec_throttler_event(struct notifier_block *nb,
+	unsigned long queued_during_suspend, void *_notify)
+{
+	struct cros_ec_throttler *ce_thr = nb_to_ce_thr(nb);
+	u32 host_event;
+
+	host_event = cros_ec_get_host_event(ce_thr->ec);
+	if (host_event & EC_HOST_EVENT_MASK(EC_HOST_EVENT_THROTTLE_START)) {
+		throttler_set_level(ce_thr->throttler, 1);
+
+		return NOTIFY_OK;
+	} else if (host_event &
+		   EC_HOST_EVENT_MASK(EC_HOST_EVENT_THROTTLE_STOP)) {
+		throttler_set_level(ce_thr->throttler, 0);
+
+		return NOTIFY_OK;
+	}
+
+	return NOTIFY_DONE;
+}
+
+static int cros_ec_throttler_probe(struct platform_device *pdev)
+{
+	struct cros_ec_throttler *ce_thr;
+	struct device *dev = &pdev->dev;
+	struct cros_ec_dev *ec;
+	int ret;
+
+	ce_thr = devm_kzalloc(dev, sizeof(*ce_thr), GFP_KERNEL);
+	if (!ce_thr)
+		return -ENOMEM;
+
+	ec = dev_get_drvdata(pdev->dev.parent);
+	ce_thr->ec = ec->ec_dev;
+
+	/*
+	 * The core code uses the DT node of the throttler to identify its
+	 * throttling devices and rates. The CrOS EC throttler is a sub-device
+	 * of the CrOS EC MFD device and doesn't have its own device node. Use
+	 * the node of the MFD device instead.
+	 */
+	dev->of_node = ce_thr->ec->dev->of_node;
+
+	ce_thr->throttler = throttler_setup(dev);
+	if (IS_ERR(ce_thr->throttler))
+		return PTR_ERR(ce_thr->throttler);
+
+	dev_set_drvdata(dev, ce_thr);
+
+	ce_thr->nb.notifier_call = cros_ec_throttler_event;
+	ret = blocking_notifier_chain_register(&ce_thr->ec->event_notifier,
+					       &ce_thr->nb);
+	if (ret < 0) {
+		dev_err(dev, "failed to register notifier\n");
+		throttler_teardown(ce_thr->throttler);
+		return ret;
+	}
+
+	return 0;
+}
+
+static int cros_ec_throttler_remove(struct platform_device *pdev)
+{
+	struct cros_ec_throttler *ce_thr = platform_get_drvdata(pdev);
+
+	blocking_notifier_chain_unregister(&ce_thr->ec->event_notifier,
+					   &ce_thr->nb);
+
+	throttler_teardown(ce_thr->throttler);
+
+	return 0;
+}
+
+static struct platform_driver cros_ec_throttler_driver = {
+	.driver = {
+		.name = "cros-ec-throttler",
+	},
+	.probe		= cros_ec_throttler_probe,
+	.remove		= cros_ec_throttler_remove,
+};
+
+module_platform_driver(cros_ec_throttler_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Matthias Kaehlcke <mka@xxxxxxxxxxxx>");
+MODULE_DESCRIPTION("Chrome OS EC Throttler");
-- 
2.18.0.rc2.346.g013aa6912e-goog