[PATCH v4 4/7] pwm: Add support for Azoteq IQS620A PWM generator

From: Jeff LaBundy <jeff@labundy.com>
To: "lee.jones@linaro.org" <lee.jones@linaro.org>,
	"dmitry.torokhov@gmail.com" <dmitry.torokhov@gmail.com>,
	"thierry.reding@gmail.com" <thierry.reding@gmail.com>,
	"jic23@kernel.org" <jic23@kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>
Cc: "linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
	"u.kleine-koenig@pengutronix.de" <u.kleine-koenig@pengutronix.de>,
	"linux-pwm@vger.kernel.org" <linux-pwm@vger.kernel.org>,
	"knaack.h@gmx.de" <knaack.h@gmx.de>,
	"lars@metafoo.de" <lars@metafoo.de>,
	"pmeerw@pmeerw.net" <pmeerw@pmeerw.net>,
	"linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>,
	"robh+dt@kernel.org" <robh+dt@kernel.org>,
	"mark.rutland@arm.com" <mark.rutland@arm.com>,
	Jeff LaBundy <jeff@labundy.com>
Subject: [PATCH v4 4/7] pwm: Add support for Azoteq IQS620A PWM generator
Date: Fri, 17 Jan 2020 02:35:57 +0000	[thread overview]
Message-ID: <1579228475-6681-5-git-send-email-jeff@labundy.com> (raw)
In-Reply-To: <1579228475-6681-1-git-send-email-jeff@labundy.com>

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>
---
Changes in v4:
  - Updated iqs620_pwm_apply and iqs620_pwm_get_state to hold the lock around
    only the minimum necessary code
  - Removed the completion protecting against early use of chip->pwms[0] from
    inside iqs620_pwm_notifier in favor of cached register values
  - Updated iqs620_pwm_get_state to use the cached register values instead of
    reading IQS620_PWR_SETTINGS_PWM_OUT and IQS620_PWM_DUTY_CYCLE (both equal
    to zero by default)
  - Added a comment in iqs620_pwm_notifier to note that the parent MFD driver
    prints an error message in the event of a device reset

Changes in v3:
  - Updated the commit message to say "~0.4%" instead of "0.4%"
  - Clarified the effect of duty cycle and state changes in the 'Limitations'
    section and added a restriction regarding 0% duty cycle
  - Added a comment in iqs620_pwm_apply to explain how duty cycle is derived
  - Updated iqs620_pwm_apply to disable the output first and enable it last to
    prevent temporarily driving a stale duty cycle
  - Rounded the calculation for duty cycle up and down in iqs620_pwm_get_state
    and iqs620_pwm_apply, respectively
  - Added a comment in iqs620_pwm_get_state to explain what it reports follow-
    ing requests to set duty cycle to 0%
  - Added a lock to prevent back-to-back access of IQS620_PWR_SETTINGS_PWM_OUT
    and IQS620_PWM_DUTY_CYCLE from being interrupted
  - Updated iqs620_pwm_notifier to reference pwm->state directly as opposed to
    calling pwm_get_state
  - Moved notifier unregistration back to a device-managed action
  - Added a completion to prevent iqs620_pwm_notifier from referencing the
    pwm_chip structure until it has been initialized by pwmchip_add

Changes in v2:
  - Merged 'Copyright' and 'Author' lines into one in introductory comments
  - Added 'Limitations' section to introductory comments
  - Replaced 'error' with 'ret' throughout
  - Added const qualifier to state argument of iqs620_pwm_apply and removed all
    modifications to the variable's contents
  - Updated iqs620_pwm_apply to return -ENOTSUPP or -EINVAL if the requested
    polarity is inverted or the requested period is below 1 ms, respectively
  - Updated iqs620_pwm_apply to disable the PWM output if duty cycle is zero
  - Added iqs620_pwm_get_state
  - Eliminated tabbed alignment of pwm_ops and platform_driver struct members
  - Moved notifier unregistration to already present iqs620_pwm_remove, which
    eliminated the need for a device-managed action and ready flag
  - Added a comment in iqs620_pwm_probe to explain the order of operations
  - Changed Kconfig "depends on" logic to MFD_IQS62X || COMPILE_TEST

 drivers/pwm/Kconfig       |  10 ++
 drivers/pwm/Makefile      |   1 +
 drivers/pwm/pwm-iqs620a.c | 258 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 269 insertions(+)
 create mode 100644 drivers/pwm/pwm-iqs620a.c

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index bd21655..60bcf6c 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -222,6 +222,16 @@ 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
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index 9a47507..a59c710 100644
--- a/drivers/pwm/Makefile
+++ b/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
diff --git a/drivers/pwm/pwm-iqs620a.c b/drivers/pwm/pwm-iqs620a.c
new file mode 100644
index 0000000..75ca482
--- /dev/null
+++ b/drivers/pwm/pwm-iqs620a.c
@@ -0,0 +1,258 @@
+// 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 on-board 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->map, 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->map, 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->map, 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->map, IQS620_PWM_DUTY_CYCLE,
+			   iqs620_pwm->duty_val);
+	if (ret)
+		goto err_mutex;
+
+	ret = regmap_update_bits(iqs62x->map, 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 iqs620_pwm_private *iqs620_pwm;
+	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 = dev_get_drvdata(pdev->dev.parent);
+
+	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 = IQS620_DRV_NAME_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:" IQS620_DRV_NAME_PWM);
--
2.7.4

