pwm: Add a driver for the STMPE PWM

This adds a driver for the PWM block found in chips of the STMPE 24xx
series of multi-purpose I2C expanders. (I think STMPE means ST
Microelectronics Multi-Purpose Expander.) This PWM was designed in
accordance with Nokia specifications and is kind of weird and usually
just switched between max and zero duty cycle. However it is indeed a
PWM so it needs to live in the PWM subsystem.

This PWM is mostly used for white LED backlight.

Cc: Lee Jones <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>

drivers/pwm/Kconfig

···
 	  To compile this driver as a module, choose M here: the module
 	  will be called pwm-sti.
 
+config PWM_STMPE
+	bool "STMPE expander PWM export"
+	depends on MFD_STMPE
+	help
+	  This enables support for the PWMs found in the STMPE I/O
+	  expanders.
+
 config PWM_SUN4I
 	tristate "Allwinner PWM support"
 	depends on ARCH_SUNXI || COMPILE_TEST

drivers/pwm/Makefile

···
 obj-$(CONFIG_PWM_SAMSUNG)	+= pwm-samsung.o
 obj-$(CONFIG_PWM_SPEAR)		+= pwm-spear.o
 obj-$(CONFIG_PWM_STI)		+= pwm-sti.o
+obj-$(CONFIG_PWM_STMPE)		+= pwm-stmpe.o
 obj-$(CONFIG_PWM_SUN4I)		+= pwm-sun4i.o
 obj-$(CONFIG_PWM_TEGRA)		+= pwm-tegra.o
 obj-$(CONFIG_PWM_TIECAP)	+= pwm-tiecap.o

drivers/pwm/pwm-stmpe.c

···
+/*
+ * Copyright (C) 2016 Linaro Ltd.
+ *
+ * Author: Linus Walleij <[e-mail]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/bitops.h>
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/mfd/stmpe.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+#include <linux/slab.h>
+
+#define STMPE24XX_PWMCS		0x30
+#define PWMCS_EN_PWM0		BIT(0)
+#define PWMCS_EN_PWM1		BIT(1)
+#define PWMCS_EN_PWM2		BIT(2)
+#define STMPE24XX_PWMIC0	0x38
+#define STMPE24XX_PWMIC1	0x39
+#define STMPE24XX_PWMIC2	0x3a
+
+#define STMPE_PWM_24XX_PINBASE	21
+
+struct stmpe_pwm {
+	struct stmpe *stmpe;
+	struct pwm_chip chip;
+	u8 last_duty;
+};
+
+static inline struct stmpe_pwm *to_stmpe_pwm(struct pwm_chip *chip)
+{
+	return container_of(chip, struct stmpe_pwm, chip);
+}
+
+static int stmpe_24xx_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
+{
+	struct stmpe_pwm *stmpe_pwm = to_stmpe_pwm(chip);
+	u8 value;
+	int ret;
+
+	ret = stmpe_reg_read(stmpe_pwm->stmpe, STMPE24XX_PWMCS);
+	if (ret < 0) {
+		dev_err(chip->dev, "error reading PWM#%u control\n",
+			pwm->hwpwm);
+		return ret;
+	}
+
+	value = ret | BIT(pwm->hwpwm);
+
+	ret = stmpe_reg_write(stmpe_pwm->stmpe, STMPE24XX_PWMCS, value);
+	if (ret) {
+		dev_err(chip->dev, "error writing PWM#%u control\n",
+			pwm->hwpwm);
+		return ret;
+	}
+
+	return 0;
+}
+
+static void stmpe_24xx_pwm_disable(struct pwm_chip *chip,
+				   struct pwm_device *pwm)
+{
+	struct stmpe_pwm *stmpe_pwm = to_stmpe_pwm(chip);
+	u8 value;
+	int ret;
+
+	ret = stmpe_reg_read(stmpe_pwm->stmpe, STMPE24XX_PWMCS);
+	if (ret < 0) {
+		dev_err(chip->dev, "error reading PWM#%u control\n",
+			pwm->hwpwm);
+		return;
+	}
+
+	value = ret & ~BIT(pwm->hwpwm);
+
+	ret = stmpe_reg_write(stmpe_pwm->stmpe, STMPE24XX_PWMCS, value);
+	if (ret) {
+		dev_err(chip->dev, "error writing PWM#%u control\n",
+			pwm->hwpwm);
+		return;
+	}
+}
+
+/* STMPE 24xx PWM instructions */
+#define SMAX		0x007f
+#define SMIN		0x00ff
+#define GTS		0x0000
+#define LOAD		BIT(14) /* Only available on 2403 */
+#define RAMPUP		0x0000
+#define RAMPDOWN	BIT(7)
+#define PRESCALE_512	BIT(14)
+#define STEPTIME_1	BIT(8)
+#define BRANCH		(BIT(15) | BIT(13))
+
+static int stmpe_24xx_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
+				 int duty_ns, int period_ns)
+{
+	struct stmpe_pwm *stmpe_pwm = to_stmpe_pwm(chip);
+	unsigned int i, pin;
+	u16 program[3] = {
+		SMAX,
+		GTS,
+		GTS,
+	};
+	u8 offset;
+	int ret;
+
+	/* Make sure we are disabled */
+	if (pwm_is_enabled(pwm)) {
+		stmpe_24xx_pwm_disable(chip, pwm);
+	} else {
+		/* Connect the PWM to the pin */
+		pin = pwm->hwpwm;
+
+		/* On STMPE2401 and 2403 pins 21,22,23 are used */
+		if (stmpe_pwm->stmpe->partnum == STMPE2401 ||
+		    stmpe_pwm->stmpe->partnum == STMPE2403)
+			pin += STMPE_PWM_24XX_PINBASE;
+
+		ret = stmpe_set_altfunc(stmpe_pwm->stmpe, BIT(pin),
+					STMPE_BLOCK_PWM);
+		if (ret) {
+			dev_err(chip->dev, "unable to connect PWM#%u to pin\n",
+				pwm->hwpwm);
+			return ret;
+		}
+	}
+
+	/* STMPE24XX */
+	switch (pwm->hwpwm) {
+	case 0:
+		offset = STMPE24XX_PWMIC0;
+		break;
+
+	case 1:
+		offset = STMPE24XX_PWMIC1;
+		break;
+
+	case 2:
+		offset = STMPE24XX_PWMIC1;
+		break;
+
+	default:
+		/* Should not happen as npwm is 3 */
+		return -ENODEV;
+	}
+
+	dev_dbg(chip->dev, "PWM#%u: config duty %d ns, period %d ns\n",
+		pwm->hwpwm, duty_ns, period_ns);
+
+	if (duty_ns == 0) {
+		if (stmpe_pwm->stmpe->partnum == STMPE2401)
+			program[0] = SMAX; /* off all the time */
+
+		if (stmpe_pwm->stmpe->partnum == STMPE2403)
+			program[0] = LOAD | 0xff; /* LOAD 0xff */
+
+		stmpe_pwm->last_duty = 0x00;
+	} else if (duty_ns == period_ns) {
+		if (stmpe_pwm->stmpe->partnum == STMPE2401)
+			program[0] = SMIN; /* on all the time */
+
+		if (stmpe_pwm->stmpe->partnum == STMPE2403)
+			program[0] = LOAD | 0x00; /* LOAD 0x00 */
+
+		stmpe_pwm->last_duty = 0xff;
+	} else {
+		u8 value, last = stmpe_pwm->last_duty;
+		unsigned long duty;
+
+		/*
+		 * Counter goes from 0x00 to 0xff repeatedly at 32768 Hz,
+		 * (means a period of 30517 ns) then this is compared to the
+		 * counter from the ramp, if this is >= PWM counter the output
+		 * is high. With LOAD we can define how much of the cycle it
+		 * is on.
+		 *
+		 * Prescale = 0 -> 2 kHz -> T = 1/f = 488281.25 ns
+		 */
+
+		/* Scale to 0..0xff */
+		duty = duty_ns * 256;
+		duty = DIV_ROUND_CLOSEST(duty, period_ns);
+		value = duty;
+
+		if (value == last) {
+			/* Run the old program */
+			if (pwm_is_enabled(pwm))
+				stmpe_24xx_pwm_enable(chip, pwm);
+
+			return 0;
+		} else if (stmpe_pwm->stmpe->partnum == STMPE2403) {
+			/* STMPE2403 can simply set the right PWM value */
+			program[0] = LOAD | value;
+			program[1] = 0x0000;
+		} else if (stmpe_pwm->stmpe->partnum == STMPE2401) {
+			/* STMPE2401 need a complex program */
+			u16 incdec = 0x0000;
+
+			if (last < value)
+				/* Count up */
+				incdec = RAMPUP | (value - last);
+			else
+				/* Count down */
+				incdec = RAMPDOWN | (last - value);
+
+			/* Step to desired value, smoothly */
+			program[0] = PRESCALE_512 | STEPTIME_1 | incdec;
+
+			/* Loop eternally to 0x00 */
+			program[1] = BRANCH;
+		}
+
+		dev_dbg(chip->dev,
+			"PWM#%u: value = %02x, last_duty = %02x, program=%04x,%04x,%04x\n",
+			pwm->hwpwm, value, last, program[0], program[1],
+			program[2]);
+		stmpe_pwm->last_duty = value;
+	}
+
+	/*
+	 * We can write programs of up to 64 16-bit words into this channel.
+	 */
+	for (i = 0; i < ARRAY_SIZE(program); i++) {
+		u8 value;
+
+		value = (program[i] >> 8) & 0xff;
+
+		ret = stmpe_reg_write(stmpe_pwm->stmpe, offset, value);
+		if (ret) {
+			dev_err(chip->dev, "error writing register %02x: %d\n",
+				offset, ret);
+			return ret;
+		}
+
+		value = program[i] & 0xff;
+
+		ret = stmpe_reg_write(stmpe_pwm->stmpe, offset, value);
+		if (ret) {
+			dev_err(chip->dev, "error writing register %02x: %d\n",
+				offset, ret);
+			return ret;
+		}
+	}
+
+	/* If we were enabled, re-enable this PWM */
+	if (pwm_is_enabled(pwm))
+		stmpe_24xx_pwm_enable(chip, pwm);
+
+	/* Sleep for 200ms so we're sure it will take effect */
+	msleep(200);
+
+	dev_dbg(chip->dev, "programmed PWM#%u, %u bytes\n", pwm->hwpwm, i);
+
+	return 0;
+}
+
+static const struct pwm_ops stmpe_24xx_pwm_ops = {
+	.config = stmpe_24xx_pwm_config,
+	.enable = stmpe_24xx_pwm_enable,
+	.disable = stmpe_24xx_pwm_disable,
+	.owner = THIS_MODULE,
+};
+
+static int __init stmpe_pwm_probe(struct platform_device *pdev)
+{
+	struct stmpe *stmpe = dev_get_drvdata(pdev->dev.parent);
+	struct stmpe_pwm *pwm;
+	int ret;
+
+	pwm = devm_kzalloc(&pdev->dev, sizeof(*pwm), GFP_KERNEL);
+	if (!pwm)
+		return -ENOMEM;
+
+	pwm->stmpe = stmpe;
+	pwm->chip.dev = &pdev->dev;
+	pwm->chip.base = -1;
+
+	if (stmpe->partnum == STMPE2401 || stmpe->partnum == STMPE2403) {
+		pwm->chip.ops = &stmpe_24xx_pwm_ops;
+		pwm->chip.npwm = 3;
+	} else {
+		if (stmpe->partnum == STMPE1601)
+			dev_err(&pdev->dev, "STMPE1601 not yet supported\n");
+		else
+			dev_err(&pdev->dev, "Unknown STMPE PWM\n");
+
+		return -ENODEV;
+	}
+
+	ret = stmpe_enable(stmpe, STMPE_BLOCK_PWM);
+	if (ret)
+		return ret;
+
+	ret = pwmchip_add(&pwm->chip);
+	if (ret) {
+		stmpe_disable(stmpe, STMPE_BLOCK_PWM);
+		return ret;
+	}
+
+	platform_set_drvdata(pdev, pwm);
+
+	return 0;
+}
+
+static struct platform_driver stmpe_pwm_driver = {
+	.driver = {
+		.name = "stmpe-pwm",
+	},
+};
+builtin_platform_driver_probe(stmpe_pwm_driver, stmpe_pwm_probe);