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Cc:     Lee Jones <lee.jones@linaro.org>, Rob Herring <robh+dt@kernel.org>,
        =?UTF-8?q?Jonathan=20Neusch=C3=A4fer?= <j.neuschaefer@gmx.net>,
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        <u.kleine-koenig@pengutronix.de>,
        Alessandro Zummo <a.zummo@towertech.it>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>,
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        Sam Ravnborg <sam@ravnborg.org>,
        Linus Walleij <linus.walleij@linaro.org>,
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        Lubomir Rintel <lkundrak@v3.sk>,
        Mark Brown <broonie@kernel.org>, allen <allen.chen@ite.com.tw>,
        Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        devicetree@vger.kernel.org, linux-pwm@vger.kernel.org,
        linux-rtc@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        Heiko Stuebner <heiko@sntech.de>,
        Josua Mayer <josua.mayer@jm0.eu>,
        Andreas Kemnade <andreas@kemnade.info>,
        Arnd Bergmann <arnd@arndb.de>, Daniel Palmer <daniel@0x0f.com>
Subject: [PATCH v2 05/10] pwm: ntxec: Add driver for PWM function in Netronix EC
Date:   Sat,  5 Sep 2020 15:32:25 +0200
Message-Id: <20200905133230.1014581-6-j.neuschaefer@gmx.net>
In-Reply-To: <20200905133230.1014581-1-j.neuschaefer@gmx.net>
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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 Neusch=C3=A4fer <j.neuschaefer@gmx.net>
=2D--

v2:
- Various grammar and style improvements, as suggested by Uwe Kleine-K=C3=
=B6nig,
  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
=2D--
 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
=2D-- 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
=2D-- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -32,6 +32,7 @@ obj-$(CONFIG_PWM_MESON)		+=3D pwm-meson.o
 obj-$(CONFIG_PWM_MEDIATEK)	+=3D pwm-mediatek.o
 obj-$(CONFIG_PWM_MTK_DISP)	+=3D pwm-mtk-disp.o
 obj-$(CONFIG_PWM_MXS)		+=3D pwm-mxs.o
+obj-$(CONFIG_PWM_NTXEC)		+=3D pwm-ntxec.o
 obj-$(CONFIG_PWM_OMAP_DMTIMER)	+=3D pwm-omap-dmtimer.o
 obj-$(CONFIG_PWM_PCA9685)	+=3D pwm-pca9685.o
 obj-$(CONFIG_PWM_PXA)		+=3D pwm-pxa.o
diff --git a/drivers/pwm/pwm-ntxec.c b/drivers/pwm/pwm-ntxec.c
new file mode 100644
index 0000000000000..325ec0e8f1996
=2D-- /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 Neusch=C3=A4fer
+ */
+
+#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 regi=
ster */
+#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 bas=
e 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 =3D pwmchip_to_pwm(pwm_dev->chip);
+	unsigned int duty =3D state->duty_cycle;
+	unsigned int period =3D state->period;
+	int res =3D 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 /=3D TIME_BASE_NS;
+	duty /=3D TIME_BASE_NS;
+
+	res |=3D regmap_write(pwm->ec->regmap, NTXEC_REG_PERIOD_HIGH, u8_to_reg(=
period >> 8));
+	res |=3D regmap_write(pwm->ec->regmap, NTXEC_REG_PERIOD_LOW, u8_to_reg(p=
eriod));
+	res |=3D regmap_write(pwm->ec->regmap, NTXEC_REG_DUTY_HIGH, u8_to_reg(du=
ty >> 8));
+	res |=3D regmap_write(pwm->ec->regmap, NTXEC_REG_DUTY_LOW, u8_to_reg(dut=
y));
+
+	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=3D0 when the duty cycle is zero.
+	 */
+	if (state->enabled && duty !=3D 0) {
+		res |=3D regmap_write(pwm->ec->regmap, NTXEC_REG_ENABLE, u8_to_reg(1));
+
+		/* Disable the auto-off timer */
+		res |=3D regmap_write(pwm->ec->regmap, NTXEC_REG_AUTO_OFF_HI, u8_to_reg=
(0xff));
+		res |=3D 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 =3D {
+	.apply =3D ntxec_pwm_apply,
+	.owner =3D THIS_MODULE,
+};
+
+static int ntxec_pwm_probe(struct platform_device *pdev)
+{
+	struct ntxec *ec =3D dev_get_drvdata(pdev->dev.parent);
+	struct ntxec_pwm *pwm;
+	struct pwm_chip *chip;
+	int res;
+
+	pwm =3D devm_kzalloc(&pdev->dev, sizeof(*pwm), GFP_KERNEL);
+	if (!pwm)
+		return -ENOMEM;
+
+	pwm->ec =3D ec;
+	pwm->dev =3D &pdev->dev;
+
+	chip =3D &pwm->chip;
+	chip->dev =3D &pdev->dev;
+	chip->ops =3D &ntxec_pwm_ops;
+	chip->base =3D -1;
+	chip->npwm =3D 1;
+
+	res =3D 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 =3D platform_get_drvdata(pdev);
+	struct pwm_chip *chip =3D &pwm->chip;
+
+	return pwmchip_remove(chip);
+}
+
+static const struct of_device_id ntxec_pwm_of_match[] =3D {
+	{ .compatible =3D "netronix,ntxec-pwm" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, ntxec_pwm_of_match);
+
+static struct platform_driver ntxec_pwm_driver =3D {
+	.driver =3D {
+		.name =3D "ntxec-pwm",
+		.of_match_table =3D ntxec_pwm_of_match,
+	},
+	.probe =3D ntxec_pwm_probe,
+	.remove =3D ntxec_pwm_remove,
+};
+module_platform_driver(ntxec_pwm_driver);
+
+MODULE_AUTHOR("Jonathan Neusch=C3=A4fer <j.neuschaefer@gmx.net>");
+MODULE_DESCRIPTION("PWM driver for Netronix EC");
+MODULE_LICENSE("GPL");
=2D-
2.28.0