pwm: visconti: Add Toshiba Visconti SoC PWM support

Add driver for the PWM controller on Toshiba Visconti ARM SoC.

Signed-off-by: Nobuhiro Iwamatsu <[e-mail]>
Reviewed-by: Uwe Kleine-König <[e-mail]>
[[e-mail]: fix up a couple of checkpatch warnings]
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-twl-led.
 
+config PWM_VISCONTI
+	tristate "Toshiba Visconti PWM support"
+	depends on ARCH_VISCONTI || COMPILE_TEST
+	help
+	  PWM Subsystem driver support for Toshiba Visconti SoCs.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called pwm-visconti.
+
 config PWM_VT8500
 	tristate "vt8500 PWM support"
 	depends on ARCH_VT8500 || COMPILE_TEST

drivers/pwm/Makefile

···
 obj-$(CONFIG_PWM_TIEHRPWM)	+= pwm-tiehrpwm.o
 obj-$(CONFIG_PWM_TWL)		+= pwm-twl.o
 obj-$(CONFIG_PWM_TWL_LED)	+= pwm-twl-led.o
+obj-$(CONFIG_PWM_VISCONTI)	+= pwm-visconti.o
 obj-$(CONFIG_PWM_VT8500)	+= pwm-vt8500.o

drivers/pwm/pwm-visconti.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Toshiba Visconti pulse-width-modulation controller driver
+ *
+ * Copyright (c) 2020 - 2021 TOSHIBA CORPORATION
+ * Copyright (c) 2020 - 2021 Toshiba Electronic Devices & Storage Corporation
+ *
+ * Authors: Nobuhiro Iwamatsu <[e-mail]>
+ *
+ * Limitations:
+ * - The fixed input clock is running at 1 MHz and is divided by either 1,
+ *   2, 4 or 8.
+ * - When the settings of the PWM are modified, the new values are shadowed
+ *   in hardware until the PIPGM_PCSR register is written and the currently
+ *   running period is completed. This way the hardware switches atomically
+ *   from the old setting to the new.
+ * - Disabling the hardware completes the currently running period and keeps
+ *   the output at low level at all times.
+ */
+
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+
+#define PIPGM_PCSR(ch) (0x400 + 4 * (ch))
+#define PIPGM_PDUT(ch) (0x420 + 4 * (ch))
+#define PIPGM_PWMC(ch) (0x440 + 4 * (ch))
+
+#define PIPGM_PWMC_PWMACT		BIT(5)
+#define PIPGM_PWMC_CLK_MASK		GENMASK(1, 0)
+#define PIPGM_PWMC_POLARITY_MASK	GENMASK(5, 5)
+
+struct visconti_pwm_chip {
+	struct pwm_chip chip;
+	void __iomem *base;
+};
+
+static inline struct visconti_pwm_chip *visconti_pwm_from_chip(struct pwm_chip *chip)
+{
+	return container_of(chip, struct visconti_pwm_chip, chip);
+}
+
+static int visconti_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
+			      const struct pwm_state *state)
+{
+	struct visconti_pwm_chip *priv = visconti_pwm_from_chip(chip);
+	u32 period, duty_cycle, pwmc0;
+
+	if (!state->enabled) {
+		writel(0, priv->base + PIPGM_PCSR(pwm->hwpwm));
+		return 0;
+	}
+
+	/*
+	 * The biggest period the hardware can provide is
+	 *	(0xffff << 3) * 1000 ns
+	 * This value fits easily in an u32, so simplify the maths by
+	 * capping the values to 32 bit integers.
+	 */
+	if (state->period > (0xffff << 3) * 1000)
+		period = (0xffff << 3) * 1000;
+	else
+		period = state->period;
+
+	if (state->duty_cycle > period)
+		duty_cycle = period;
+	else
+		duty_cycle = state->duty_cycle;
+
+	/*
+	 * The input clock runs fixed at 1 MHz, so we have only
+	 * microsecond resolution and so can divide by
+	 * NSEC_PER_SEC / CLKFREQ = 1000 without losing precision.
+	 */
+	period /= 1000;
+	duty_cycle /= 1000;
+
+	if (!period)
+		return -ERANGE;
+
+	/*
+	 * PWMC controls a divider that divides the input clk by a
+	 * power of two between 1 and 8. As a smaller divider yields
+	 * higher precision, pick the smallest possible one.
+	 */
+	if (period > 0xffff) {
+		pwmc0 = ilog2(period >> 16);
+		if (WARN_ON(pwmc0 > 3))
+			return -EINVAL;
+	} else {
+		pwmc0 = 0;
+	}
+
+	period >>= pwmc0;
+	duty_cycle >>= pwmc0;
+
+	if (state->polarity == PWM_POLARITY_INVERSED)
+		pwmc0 |= PIPGM_PWMC_PWMACT;
+	writel(pwmc0, priv->base + PIPGM_PWMC(pwm->hwpwm));
+	writel(duty_cycle, priv->base + PIPGM_PDUT(pwm->hwpwm));
+	writel(period, priv->base + PIPGM_PCSR(pwm->hwpwm));
+
+	return 0;
+}
+
+static void visconti_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
+				   struct pwm_state *state)
+{
+	struct visconti_pwm_chip *priv = visconti_pwm_from_chip(chip);
+	u32 period, duty, pwmc0, pwmc0_clk;
+
+	period = readl(priv->base + PIPGM_PCSR(pwm->hwpwm));
+	duty = readl(priv->base + PIPGM_PDUT(pwm->hwpwm));
+	pwmc0 = readl(priv->base + PIPGM_PWMC(pwm->hwpwm));
+	pwmc0_clk = pwmc0 & PIPGM_PWMC_CLK_MASK;
+
+	state->period = (period << pwmc0_clk) * NSEC_PER_USEC;
+	state->duty_cycle = (duty << pwmc0_clk) * NSEC_PER_USEC;
+	if (pwmc0 & PIPGM_PWMC_POLARITY_MASK)
+		state->polarity = PWM_POLARITY_INVERSED;
+	else
+		state->polarity = PWM_POLARITY_NORMAL;
+
+	state->enabled = true;
+}
+
+static const struct pwm_ops visconti_pwm_ops = {
+	.apply = visconti_pwm_apply,
+	.get_state = visconti_pwm_get_state,
+	.owner = THIS_MODULE,
+};
+
+static int visconti_pwm_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct visconti_pwm_chip *priv;
+	int ret;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->base))
+		return PTR_ERR(priv->base);
+
+	platform_set_drvdata(pdev, priv);
+
+	priv->chip.dev = dev;
+	priv->chip.ops = &visconti_pwm_ops;
+	priv->chip.npwm = 4;
+
+	ret = pwmchip_add(&priv->chip);
+	if (ret < 0)
+		return dev_err_probe(&pdev->dev, ret, "Cannot register visconti PWM\n");
+
+	return 0;
+}
+
+static int visconti_pwm_remove(struct platform_device *pdev)
+{
+	struct visconti_pwm_chip *priv = platform_get_drvdata(pdev);
+
+	pwmchip_remove(&priv->chip);
+
+	return 0;
+}
+
+static const struct of_device_id visconti_pwm_of_match[] = {
+	{ .compatible = "toshiba,visconti-pwm", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, visconti_pwm_of_match);
+
+static struct platform_driver visconti_pwm_driver = {
+	.driver = {
+		.name = "pwm-visconti",
+		.of_match_table = visconti_pwm_of_match,
+	},
+	.probe = visconti_pwm_probe,
+	.remove = visconti_pwm_remove,
+};
+module_platform_driver(visconti_pwm_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Nobuhiro Iwamatsu <[e-mail]>");
+MODULE_ALIAS("platform:pwm-visconti");