[PATCH v2 05/10] pwm: ntxec: Add driver for PWM function in Netronix EC

Jonathan Neuschäfer
2020-09-05T13:53:20Z

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

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
---

v2:
- Various grammar and style improvements, as suggested by Uwe Kleine-König,
Lee Jones, and Alexandre Belloni
- Switch to regmap
- Prefix registers with NTXEC_REG_
- Add help text to the Kconfig option
- Use the .apply callback instead of the old API
- Add a #define for the time base (125ns)
- Don't change device state in .probe; this avoids multiple problems
- Rework division and overflow check logic to perform divisions in 32 bits
- Avoid setting duty cycle to zero, to work around a hardware quirk
---
drivers/pwm/Kconfig | 8 ++
drivers/pwm/Makefile | 1 +
drivers/pwm/pwm-ntxec.c | 160 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 169 insertions(+)
create mode 100644 drivers/pwm/pwm-ntxec.c

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 7dbcf6973d335..7fd17c6cda95e 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -350,6 +350,14 @@ 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
+ help
+ Say yes here if you want to support the PWM output of the embedded
+ controller found in certain e-book readers designed by the ODM
+ Netronix.
+
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 2c2ba0a035577..1cc50dba22d1b 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_PXA) += pwm-pxa.o
diff --git a/drivers/pwm/pwm-ntxec.c b/drivers/pwm/pwm-ntxec.c
new file mode 100644
index 0000000000000..325ec0e8f1996
--- /dev/null
+++ b/drivers/pwm/pwm-ntxec.c
@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * The Netronix embedded controller is a microcontroller found in some
+ * e-book readers designed by the ODM Netronix, Inc. It contains RTC,
+ * battery monitoring, system power management, and PWM functionality.
+ *
+ * This driver implements PWM output.
+ *
+ * Copyright 2020 Jonathan Neuschäfer
+ */
+
+#include <linux/mfd/ntxec.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+#include <linux/regmap.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_REG_AUTO_OFF_HI 0xa1
+#define NTXEC_REG_AUTO_OFF_LO 0xa2
+#define NTXEC_REG_ENABLE 0xa3
+#define NTXEC_REG_PERIOD_LOW 0xa4
+#define NTXEC_REG_PERIOD_HIGH 0xa5
+#define NTXEC_REG_DUTY_LOW 0xa6
+#define NTXEC_REG_DUTY_HIGH 0xa7
+
+/* Convert an 8-bit value into the correct format for writing into a register */
+#define u8_to_reg(x) (((x) & 0xff) << 8)
+
+/*
+ * The time base used in the EC is 8MHz, or 125ns. Period and duty cycle are
+ * measured in this unit.
+ */
+#define TIME_BASE_NS 125
+
+/*
+ * The maximum input value (in nanoseconds) is determined by the time base and
+ * the range of the hardware registers that hold the converted value.
+ * It fits into 32 bits, so we can do our calculations in 32 bits as well.
+ */
+#define MAX_PERIOD_NS (TIME_BASE_NS * 0x10000 - 1)
+
+static int ntxec_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm_dev,
+ const struct pwm_state *state)
+{
+ struct ntxec_pwm *pwm = pwmchip_to_pwm(pwm_dev->chip);
+ unsigned int duty = state->duty_cycle;
+ unsigned int period = state->period;
+ int res = 0;
+
+ if (period > MAX_PERIOD_NS) {
+ dev_warn(pwm->dev,
+ "Period is not representable in 16 bits after division by %u: %u\n",
+ TIME_BASE_NS, period);
+ return -ERANGE;
+ }
+
+ period /= TIME_BASE_NS;
+ duty /= TIME_BASE_NS;
+
+ res |= regmap_write(pwm->ec->regmap, NTXEC_REG_PERIOD_HIGH, u8_to_reg(period >> 8));
+ res |= regmap_write(pwm->ec->regmap, NTXEC_REG_PERIOD_LOW, u8_to_reg(period));
+ res |= regmap_write(pwm->ec->regmap, NTXEC_REG_DUTY_HIGH, u8_to_reg(duty >> 8));
+ res |= regmap_write(pwm->ec->regmap, NTXEC_REG_DUTY_LOW, u8_to_reg(duty));
+
+ if (res < 0)
+ return -EIO;
+
+ /*
+ * Writing a duty cycle of zone puts the device into a state where
+ * writing a higher duty cycle doesn't result in the brightness that it
+ * usually results in. This can be fixed by cycling the ENABLE register.
+ *
+ * As a workaround, write ENABLE=0 when the duty cycle is zero.
+ */
+ if (state->enabled && duty != 0) {
+ res |= regmap_write(pwm->ec->regmap, NTXEC_REG_ENABLE, u8_to_reg(1));
+
+ /* Disable the auto-off timer */
+ res |= regmap_write(pwm->ec->regmap, NTXEC_REG_AUTO_OFF_HI, u8_to_reg(0xff));
+ res |= regmap_write(pwm->ec->regmap, NTXEC_REG_AUTO_OFF_LO, u8_to_reg(0xff));
+ return res ? -EIO : 0;
+ } else {
+ return regmap_write(pwm->ec->regmap, NTXEC_REG_ENABLE, u8_to_reg(0));
+ }
+}
+
+static struct pwm_ops ntxec_pwm_ops = {
+ .apply = ntxec_pwm_apply,
+ .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);
+
+ 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@gmx.net>");
+MODULE_DESCRIPTION("PWM driver for Netronix EC");
+MODULE_LICENSE("GPL");
--
2.28.0