tach: Add show_rpm attribute on pwm-tegra-tach

Below changes are supported:
  - Added show rpm attribute to pwm-tegra-tachometer
  - Added HWMON registration for pwm-tegra-tachometer
  - Disbale interrupt to skip overrun/underrun configurations, so that
    rpm regiseter is configured properly to provide correct rpm reading.

Bug 3771589

Change-Id: Ie4a45eab03c4dbefb3b5abfd76f8dba8909d61ec
Signed-off-by: Sandipan Patra <spatra@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nv-oot/+/2768987
Reviewed-by: Bibek Basu <bbasu@nvidia.com>
Reviewed-by: Krishna Yarlagadda <kyarlagadda@nvidia.com>
GVS: Gerrit_Virtual_Submit <buildbot_gerritrpt@nvidia.com>

drivers/pwm/pwm-tegra-tachometer.c

@@ -12,7 +12,9 @@
 #include <linux/reset.h>
 #include <linux/of_device.h>
 #include <linux/io.h>
-#define DRIVER_NAME "pwm-tach"
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#define DRIVER_NAME "pwm_tach"
 
 /* Since oscillator clock (38.4MHz) serves as a clock source for
  * the tach input controller, 1.0105263MHz (i.e. 38.4/38) has to be
@@ -91,6 +93,37 @@ struct pwm_tegra_tach {
 	const struct pwm_tegra_tach_soc_data	*soc_data;
 };
 
+static ssize_t rpm_show(struct device *dev, struct device_attribute *attr,
+			char *buf)
+{
+	struct pwm_tegra_tach *ptt = dev_get_drvdata(dev);
+	struct pwm_device *pwm = &ptt->chip.pwms[0];
+	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 DEVICE_ATTR_RO(rpm);
+
+static struct attribute *pwm_tach_attrs[] = {
+	&dev_attr_rpm.attr,
+	NULL,
+};
+
+ATTRIBUTE_GROUPS(pwm_tach);
+
 static struct pwm_tegra_tach *to_tegra_pwm_chip(struct pwm_chip *chip)
 {
 	return container_of(chip, struct pwm_tegra_tach, chip);
@@ -299,6 +332,7 @@ static int pwm_tegra_tach_probe(struct platform_device *pdev)
 {
 	struct pwm_tegra_tach *ptt;
 	struct pwm_device *pwm;
+	struct device *hwmon;
 	struct resource *r;
 	int ret;
 
@@ -353,7 +387,11 @@ static int pwm_tegra_tach_probe(struct platform_device *pdev)
 		goto clk_unprep;
 	}
 
-	reset_control_reset(ptt->rst);
+	ret = reset_control_reset(ptt->rst);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "Failed to reset: %d\n", ret);
+		goto clk_unprep;
+	}
 
 	if (ptt->soc_data->has_interrupt_support) {
 		ptt->irq = platform_get_irq(pdev, 0);
@@ -413,6 +451,13 @@ static int pwm_tegra_tach_probe(struct platform_device *pdev)
 				TACH_FAN_ENABLE_INTERRUPT_SHIFT);
 
 	}
+
+	hwmon = devm_hwmon_device_register_with_groups(&pdev->dev, DRIVER_NAME, ptt, pwm_tach_groups);
+	if (IS_ERR(hwmon)) {
+		dev_warn(&pdev->dev, "Failed to register hwmon device: %d\n", PTR_ERR_OR_ZERO(hwmon));
+		dev_warn(&pdev->dev, "Tegra Tachometer got registered witout hwmon sysfs support\n");
+	}
+
 	return 0;
 
 pwm_remove:
@@ -472,7 +517,7 @@ static struct pwm_tegra_tach_soc_data tegra194_tach_soc_data = {
 };
 
 static struct pwm_tegra_tach_soc_data tegra234_tach_soc_data = {
-		.has_interrupt_support = true,
+		.has_interrupt_support = false,
 };
 
 static const struct of_device_id pwm_tegra_tach_of_match[] = {