hwmon: Add pwm based generic tachometer

Add PWM based generic tachometer which capture the pwm
and report the speed.

Bug 3621819

Change-Id: I08d7fc808c3a29d6876026ce539e3467887f8112
Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nv-oot/+/2703728
GVS: Gerrit_Virtual_Submit

drivers/Makefile

@@ -3,6 +3,7 @@
 
 LINUXINCLUDE += -I$(srctree.nvidia-oot)/include
 
+obj-m += hwmon/
 obj-m += mfd/
 obj-m += thermal/
 obj-m += watchdog/

drivers/hwmon/Makefile

@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2022, NVIDIA CORPORATION.  All rights reserved.
+
+obj-m += generic-pwm-tachometer.o

drivers/hwmon/generic-pwm-tachometer.c

@@ -0,0 +1,97 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2022, NVIDIA CORPORATION.  All rights reserved.
+
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/err.h>
+#include <linux/pwm.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+
+struct pwm_hwmon_tach {
+	struct device		*dev;
+	struct pwm_device	*pwm;
+	struct device		*hwmon;
+};
+
+static ssize_t show_rpm(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct pwm_hwmon_tach *ptt = dev_get_drvdata(dev);
+	struct pwm_device *pwm = ptt->pwm;
+	struct pwm_capture result;
+	unsigned int rpm = 0;
+	int ret;
+
+	ret = pwm_capture(pwm, &result, 0);
+	if (ret < 0) {
+		dev_err(ptt->dev, "Failed to capture PWM: %d\n", ret);
+		return ret;
+	}
+
+	if (result.period)
+		rpm = DIV_ROUND_CLOSEST_ULL(60ULL * NSEC_PER_SEC,
+					    result.period);
+
+	return sprintf(buf, "%u\n", rpm);
+}
+static SENSOR_DEVICE_ATTR(rpm, 0444, show_rpm, NULL, 0);
+
+static struct attribute *pwm_tach_attrs[] = {
+	&sensor_dev_attr_rpm.dev_attr.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(pwm_tach);
+
+static int pwm_tach_probe(struct platform_device *pdev)
+{
+	struct pwm_hwmon_tach *ptt;
+
+	ptt = devm_kzalloc(&pdev->dev, sizeof(*ptt), GFP_KERNEL);
+	if (!ptt)
+		return -ENOMEM;
+
+	ptt->dev = &pdev->dev;
+
+	platform_set_drvdata(pdev, ptt);
+	dev_set_drvdata(&pdev->dev, ptt);
+
+	ptt->pwm = devm_of_pwm_get(&pdev->dev, pdev->dev.of_node, NULL);
+	if (IS_ERR(ptt->pwm)) {
+		if (PTR_ERR(ptt->pwm) != -EPROBE_DEFER) {
+			dev_err(&pdev->dev, "Failed to get pwm:  %ld\n",
+				PTR_ERR(ptt->pwm));
+		}
+		return PTR_ERR(ptt->pwm);
+	}
+
+	ptt->hwmon = devm_hwmon_device_register_with_groups(&pdev->dev,
+					 "pwm_tach", ptt, pwm_tach_groups);
+	if (IS_ERR(ptt->hwmon)) {
+		dev_err(&pdev->dev, "Failed to register hwmon device: %d\n",
+			PTR_ERR_OR_ZERO(ptt->hwmon));
+		return PTR_ERR_OR_ZERO(ptt->hwmon);
+	}
+
+	return 0;
+}
+
+static const struct of_device_id pwm_tach_of_match[] = {
+	{ .compatible = "generic-pwm-tachometer" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, pwm_tach_of_match);
+
+static struct platform_driver pwm_tach_driver = {
+	.driver = {
+		.name = "generic-pwm-tachometer",
+		.of_match_table = pwm_tach_of_match,
+	},
+	.probe = pwm_tach_probe,
+};
+
+module_platform_driver(pwm_tach_driver);
+
+MODULE_DESCRIPTION("PWM based Generic Tachometer driver");
+MODULE_AUTHOR("Laxman Dewangan <ldewangan@nvidia.com>");
+MODULE_AUTHOR("R Raj Kumar <rrajk@nvidia.com>");
+MODULE_LICENSE("GPL v2");