[RFC PATCH 06/10] pwm: ntxec: Add driver for PWM function in Netronix EC

[Jonathan Neuschäfer]

The Netronix EC provides a PWM output, which is used for the backlight
on ebook readers. This patches adds a driver for the PWM output.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer at gmx.net>
---
 drivers/pwm/Kconfig     |   4 ++
 drivers/pwm/Makefile    |   1 +
 drivers/pwm/pwm-ntxec.c | 148 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 153 insertions(+)
 create mode 100644 drivers/pwm/pwm-ntxec.c

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index cb8d739067d2f..147d6629e662c 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -350,6 +350,10 @@ config PWM_MXS
 	  To compile this driver as a module, choose M here: the module
 	  will be called pwm-mxs.

+config PWM_NTXEC
+	tristate "Netronix embedded controller PWM support"
+	depends on MFD_NTXEC && OF
+
 config PWM_OMAP_DMTIMER
 	tristate "OMAP Dual-Mode Timer PWM support"
 	depends on OF
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index a59c710e98c76..15507a6d9ca12 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -32,6 +32,7 @@ obj-$(CONFIG_PWM_MESON)		+= pwm-meson.o
 obj-$(CONFIG_PWM_MEDIATEK)	+= pwm-mediatek.o
 obj-$(CONFIG_PWM_MTK_DISP)	+= pwm-mtk-disp.o
 obj-$(CONFIG_PWM_MXS)		+= pwm-mxs.o
+obj-$(CONFIG_PWM_NTXEC)		+= pwm-ntxec.o
 obj-$(CONFIG_PWM_OMAP_DMTIMER)	+= pwm-omap-dmtimer.o
 obj-$(CONFIG_PWM_PCA9685)	+= pwm-pca9685.o
 obj-$(CONFIG_PWM_PUV3)		+= pwm-puv3.o
diff --git a/drivers/pwm/pwm-ntxec.c b/drivers/pwm/pwm-ntxec.c
new file mode 100644
index 0000000000000..eca305d8e915b
--- /dev/null
+++ b/drivers/pwm/pwm-ntxec.c
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright 2020 Jonathan Neuschäfer <j.neuschaefer at gmx.net>
+//
+// PWM driver for Netronix embedded controller.
+
+#include <linux/mfd/ntxec.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+#include <linux/of_device.h>
+#include <linux/types.h>
+
+struct ntxec_pwm {
+	struct device *dev;
+	struct ntxec *ec;
+	struct pwm_chip chip;
+};
+
+static struct ntxec_pwm *pwmchip_to_pwm(struct pwm_chip *chip)
+{
+	return container_of(chip, struct ntxec_pwm, chip);
+}
+
+#define NTXEC_UNK_A		0xa1
+#define NTXEC_UNK_B		0xa2
+#define NTXEC_ENABLE		0xa3
+#define NTXEC_PERIOD_LOW	0xa4
+#define NTXEC_PERIOD_HIGH	0xa5
+#define NTXEC_DUTY_LOW		0xa6
+#define NTXEC_DUTY_HIGH		0xa7
+
+/*
+ * The time base used in the EC is 8MHz, or 125ns. Period and duty cycle are
+ * measured in this unit.
+ */
+static int ntxec_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm_dev,
+				 int duty_ns, int period_ns)
+{
+	struct ntxec_pwm *pwm = pwmchip_to_pwm(chip);
+	uint64_t duty = duty_ns;
+	uint64_t period = period_ns;
+	int res = 0;
+
+	do_div(period, 125);
+	if (period > 0xffff) {
+		dev_warn(pwm->dev,
+			 "Period is not representable in 16 bits: %llu\n", period);
+		return -ERANGE;
+	}
+
+	do_div(duty, 125);
+	if (duty > 0xffff) {
+		dev_warn(pwm->dev, "Duty cycle is not representable in 16 bits: %llu\n",
+			duty);
+		return -ERANGE;
+	}
+
+	res |= ntxec_write8(pwm->ec, NTXEC_PERIOD_HIGH, period >> 8);
+	res |= ntxec_write8(pwm->ec, NTXEC_PERIOD_LOW, period);
+	res |= ntxec_write8(pwm->ec, NTXEC_DUTY_HIGH, duty >> 8);
+	res |= ntxec_write8(pwm->ec, NTXEC_DUTY_LOW, duty);
+
+	return (res < 0) ? -EIO : 0;
+}
+
+static int ntxec_pwm_enable(struct pwm_chip *chip,
+				 struct pwm_device *pwm_dev)
+{
+	struct ntxec_pwm *pwm = pwmchip_to_pwm(chip);
+
+	return ntxec_write8(pwm->ec, NTXEC_ENABLE, 1);
+}
+
+static void ntxec_pwm_disable(struct pwm_chip *chip,
+				   struct pwm_device *pwm_dev)
+{
+	struct ntxec_pwm *pwm = pwmchip_to_pwm(chip);
+
+	ntxec_write8(pwm->ec, NTXEC_ENABLE, 0);
+}
+
+static struct pwm_ops ntxec_pwm_ops = {
+	.config		= ntxec_pwm_config,
+	.enable		= ntxec_pwm_enable,
+	.disable	= ntxec_pwm_disable,
+	.owner		= THIS_MODULE,
+};
+
+static int ntxec_pwm_probe(struct platform_device *pdev)
+{
+	struct ntxec *ec = dev_get_drvdata(pdev->dev.parent);
+	struct ntxec_pwm *pwm;
+	struct pwm_chip *chip;
+	int res;
+
+	pwm = devm_kzalloc(&pdev->dev, sizeof(*pwm), GFP_KERNEL);
+	if (!pwm)
+		return -ENOMEM;
+
+	pwm->ec = ec;
+	pwm->dev = &pdev->dev;
+
+	chip = &pwm->chip;
+	chip->dev = &pdev->dev;
+	chip->ops = &ntxec_pwm_ops;
+	chip->base = -1;
+	chip->npwm = 1;
+
+	res = pwmchip_add(chip);
+	if (res < 0)
+		return res;
+
+	platform_set_drvdata(pdev, pwm);
+
+	res |= ntxec_write8(pwm->ec, NTXEC_ENABLE, 0);
+	res |= ntxec_write8(pwm->ec, NTXEC_UNK_A, 0xff);
+	res |= ntxec_write8(pwm->ec, NTXEC_UNK_B, 0xff);
+
+	return (res < 0) ? -EIO : 0;
+}
+
+static int ntxec_pwm_remove(struct platform_device *pdev)
+{
+	struct ntxec_pwm *pwm = platform_get_drvdata(pdev);
+	struct pwm_chip *chip = &pwm->chip;
+
+	return pwmchip_remove(chip);
+}
+
+static const struct of_device_id ntxec_pwm_of_match[] = {
+	{ .compatible = "netronix,ntxec-pwm" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, ntxec_pwm_of_match);
+
+static struct platform_driver ntxec_pwm_driver = {
+	.driver = {
+		.name = "ntxec-pwm",
+		.of_match_table = ntxec_pwm_of_match,
+	},
+	.probe = ntxec_pwm_probe,
+	.remove = ntxec_pwm_remove,
+};
+module_platform_driver(ntxec_pwm_driver);
+
+MODULE_AUTHOR("Jonathan Neuschäfer <j.neuschaefer at gmx.net>");
+MODULE_DESCRIPTION("PWM driver for Netronix EC");
+MODULE_LICENSE("GPL");
--
2.27.0