pwm: Add support for Azoteq IQS620A PWM generator

This patch adds support for the Azoteq IQS620A, capable of generating
a 1-kHz PWM output with duty cycle between ~0.4% and 100% (inclusive).

Signed-off-by: Jeff LaBundy <jeff@labundy.com>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/Kconfig

@@ -232,6 +232,16 @@ config PWM_IMX_TPM
 	  To compile this driver as a module, choose M here: the module
 	  will be called pwm-imx-tpm.
 
+config PWM_IQS620A
+	tristate "Azoteq IQS620A PWM support"
+	depends on MFD_IQS62X || COMPILE_TEST
+	help
+	  Generic PWM framework driver for the Azoteq IQS620A multi-function
+	  sensor.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called pwm-iqs620a.
+
 config PWM_JZ4740
 	tristate "Ingenic JZ47xx PWM support"
 	depends on MACH_INGENIC

drivers/pwm/Makefile

@@ -20,6 +20,7 @@ obj-$(CONFIG_PWM_IMG)		+= pwm-img.o
 obj-$(CONFIG_PWM_IMX1)		+= pwm-imx1.o
 obj-$(CONFIG_PWM_IMX27)		+= pwm-imx27.o
 obj-$(CONFIG_PWM_IMX_TPM)	+= pwm-imx-tpm.o
+obj-$(CONFIG_PWM_IQS620A)	+= pwm-iqs620a.o
 obj-$(CONFIG_PWM_JZ4740)	+= pwm-jz4740.o
 obj-$(CONFIG_PWM_LP3943)	+= pwm-lp3943.o
 obj-$(CONFIG_PWM_LPC18XX_SCT)	+= pwm-lpc18xx-sct.o

drivers/pwm/pwm-iqs620a.c

@@ -0,0 +1,270 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Azoteq IQS620A PWM Generator
+ *
+ * Copyright (C) 2019 Jeff LaBundy <jeff@labundy.com>
+ *
+ * Limitations:
+ * - The period is fixed to 1 ms and is generated continuously despite changes
+ *   to the duty cycle or enable/disable state.
+ * - Changes to the duty cycle or enable/disable state take effect immediately
+ *   and may result in a glitch during the period in which the change is made.
+ * - The device cannot generate a 0% duty cycle. For duty cycles below 1 / 256
+ *   ms, the output is disabled and relies upon an external pull-down resistor
+ *   to hold the GPIO3/LTX pin low.
+ */
+
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/mfd/iqs62x.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/notifier.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+
+#define IQS620_PWR_SETTINGS			0xD2
+#define IQS620_PWR_SETTINGS_PWM_OUT		BIT(7)
+
+#define IQS620_PWM_DUTY_CYCLE			0xD8
+
+#define IQS620_PWM_PERIOD_NS			1000000
+
+struct iqs620_pwm_private {
+	struct iqs62x_core *iqs62x;
+	struct pwm_chip chip;
+	struct notifier_block notifier;
+	struct mutex lock;
+	bool out_en;
+	u8 duty_val;
+};
+
+static int iqs620_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
+			    const struct pwm_state *state)
+{
+	struct iqs620_pwm_private *iqs620_pwm;
+	struct iqs62x_core *iqs62x;
+	int duty_scale, ret;
+
+	if (state->polarity != PWM_POLARITY_NORMAL)
+		return -ENOTSUPP;
+
+	if (state->period < IQS620_PWM_PERIOD_NS)
+		return -EINVAL;
+
+	iqs620_pwm = container_of(chip, struct iqs620_pwm_private, chip);
+	iqs62x = iqs620_pwm->iqs62x;
+
+	/*
+	 * The duty cycle generated by the device is calculated as follows:
+	 *
+	 * duty_cycle = (IQS620_PWM_DUTY_CYCLE + 1) / 256 * 1 ms
+	 *
+	 * ...where IQS620_PWM_DUTY_CYCLE is a register value between 0 and 255
+	 * (inclusive). Therefore the lowest duty cycle the device can generate
+	 * while the output is enabled is 1 / 256 ms.
+	 *
+	 * For lower duty cycles (e.g. 0), the PWM output is simply disabled to
+	 * allow an external pull-down resistor to hold the GPIO3/LTX pin low.
+	 */
+	duty_scale = state->duty_cycle * 256 / IQS620_PWM_PERIOD_NS;
+
+	mutex_lock(&iqs620_pwm->lock);
+
+	if (!state->enabled || !duty_scale) {
+		ret = regmap_update_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
+					 IQS620_PWR_SETTINGS_PWM_OUT, 0);
+		if (ret)
+			goto err_mutex;
+	}
+
+	if (duty_scale) {
+		u8 duty_val = min(duty_scale - 1, 0xFF);
+
+		ret = regmap_write(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE,
+				   duty_val);
+		if (ret)
+			goto err_mutex;
+
+		iqs620_pwm->duty_val = duty_val;
+	}
+
+	if (state->enabled && duty_scale) {
+		ret = regmap_update_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
+					 IQS620_PWR_SETTINGS_PWM_OUT, 0xFF);
+		if (ret)
+			goto err_mutex;
+	}
+
+	iqs620_pwm->out_en = state->enabled;
+
+err_mutex:
+	mutex_unlock(&iqs620_pwm->lock);
+
+	return ret;
+}
+
+static void iqs620_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
+				 struct pwm_state *state)
+{
+	struct iqs620_pwm_private *iqs620_pwm;
+
+	iqs620_pwm = container_of(chip, struct iqs620_pwm_private, chip);
+
+	mutex_lock(&iqs620_pwm->lock);
+
+	/*
+	 * Since the device cannot generate a 0% duty cycle, requests to do so
+	 * cause subsequent calls to iqs620_pwm_get_state to report the output
+	 * as disabled with duty cycle equal to that which was in use prior to
+	 * the request. This is not ideal, but is the best compromise based on
+	 * the capabilities of the device.
+	 */
+	state->enabled = iqs620_pwm->out_en;
+	state->duty_cycle = DIV_ROUND_UP((iqs620_pwm->duty_val + 1) *
+					 IQS620_PWM_PERIOD_NS, 256);
+
+	mutex_unlock(&iqs620_pwm->lock);
+
+	state->period = IQS620_PWM_PERIOD_NS;
+}
+
+static int iqs620_pwm_notifier(struct notifier_block *notifier,
+			       unsigned long event_flags, void *context)
+{
+	struct iqs620_pwm_private *iqs620_pwm;
+	struct iqs62x_core *iqs62x;
+	int ret;
+
+	if (!(event_flags & BIT(IQS62X_EVENT_SYS_RESET)))
+		return NOTIFY_DONE;
+
+	iqs620_pwm = container_of(notifier, struct iqs620_pwm_private,
+				  notifier);
+	iqs62x = iqs620_pwm->iqs62x;
+
+	mutex_lock(&iqs620_pwm->lock);
+
+	/*
+	 * The parent MFD driver already prints an error message in the event
+	 * of a device reset, so nothing else is printed here unless there is
+	 * an additional failure.
+	 */
+	ret = regmap_write(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE,
+			   iqs620_pwm->duty_val);
+	if (ret)
+		goto err_mutex;
+
+	ret = regmap_update_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
+				 IQS620_PWR_SETTINGS_PWM_OUT,
+				 iqs620_pwm->out_en ? 0xFF : 0);
+
+err_mutex:
+	mutex_unlock(&iqs620_pwm->lock);
+
+	if (ret) {
+		dev_err(iqs620_pwm->chip.dev,
+			"Failed to re-initialize device: %d\n", ret);
+		return NOTIFY_BAD;
+	}
+
+	return NOTIFY_OK;
+}
+
+static const struct pwm_ops iqs620_pwm_ops = {
+	.apply = iqs620_pwm_apply,
+	.get_state = iqs620_pwm_get_state,
+	.owner = THIS_MODULE,
+};
+
+static void iqs620_pwm_notifier_unregister(void *context)
+{
+	struct iqs620_pwm_private *iqs620_pwm = context;
+	int ret;
+
+	ret = blocking_notifier_chain_unregister(&iqs620_pwm->iqs62x->nh,
+						 &iqs620_pwm->notifier);
+	if (ret)
+		dev_err(iqs620_pwm->chip.dev,
+			"Failed to unregister notifier: %d\n", ret);
+}
+
+static int iqs620_pwm_probe(struct platform_device *pdev)
+{
+	struct iqs62x_core *iqs62x = dev_get_drvdata(pdev->dev.parent);
+	struct iqs620_pwm_private *iqs620_pwm;
+	unsigned int val;
+	int ret;
+
+	iqs620_pwm = devm_kzalloc(&pdev->dev, sizeof(*iqs620_pwm), GFP_KERNEL);
+	if (!iqs620_pwm)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, iqs620_pwm);
+	iqs620_pwm->iqs62x = iqs62x;
+
+	ret = regmap_read(iqs62x->regmap, IQS620_PWR_SETTINGS, &val);
+	if (ret)
+		return ret;
+	iqs620_pwm->out_en = val & IQS620_PWR_SETTINGS_PWM_OUT;
+
+	ret = regmap_read(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE, &val);
+	if (ret)
+		return ret;
+	iqs620_pwm->duty_val = val;
+
+	iqs620_pwm->chip.dev = &pdev->dev;
+	iqs620_pwm->chip.ops = &iqs620_pwm_ops;
+	iqs620_pwm->chip.base = -1;
+	iqs620_pwm->chip.npwm = 1;
+
+	mutex_init(&iqs620_pwm->lock);
+
+	iqs620_pwm->notifier.notifier_call = iqs620_pwm_notifier;
+	ret = blocking_notifier_chain_register(&iqs620_pwm->iqs62x->nh,
+					       &iqs620_pwm->notifier);
+	if (ret) {
+		dev_err(&pdev->dev, "Failed to register notifier: %d\n", ret);
+		return ret;
+	}
+
+	ret = devm_add_action_or_reset(&pdev->dev,
+				       iqs620_pwm_notifier_unregister,
+				       iqs620_pwm);
+	if (ret)
+		return ret;
+
+	ret = pwmchip_add(&iqs620_pwm->chip);
+	if (ret)
+		dev_err(&pdev->dev, "Failed to add device: %d\n", ret);
+
+	return ret;
+}
+
+static int iqs620_pwm_remove(struct platform_device *pdev)
+{
+	struct iqs620_pwm_private *iqs620_pwm = platform_get_drvdata(pdev);
+	int ret;
+
+	ret = pwmchip_remove(&iqs620_pwm->chip);
+	if (ret)
+		dev_err(&pdev->dev, "Failed to remove device: %d\n", ret);
+
+	return ret;
+}
+
+static struct platform_driver iqs620_pwm_platform_driver = {
+	.driver = {
+		.name = "iqs620a-pwm",
+	},
+	.probe = iqs620_pwm_probe,
+	.remove = iqs620_pwm_remove,
+};
+module_platform_driver(iqs620_pwm_platform_driver);
+
+MODULE_AUTHOR("Jeff LaBundy <jeff@labundy.com>");
+MODULE_DESCRIPTION("Azoteq IQS620A PWM Generator");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:iqs620a-pwm");