diff mbox series

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

Message ID 20200620224222.1312520-5-j.neuschaefer@gmx.net
State New
Headers show
Series [RFC,01/10] DT bindings in plain text format | expand

Commit Message

J. Neuschäfer June 20, 2020, 10:42 p.m. UTC
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@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

--
2.27.0

Comments

J. Neuschäfer July 3, 2020, 4:15 p.m. UTC | #1
On Mon, Jun 22, 2020 at 10:18:02AM +0200, Uwe Kleine-König wrote:
> Hello,

> 

> On Sun, Jun 21, 2020 at 12:42:17AM +0200, Jonathan Neuschäfer wrote:

> > The Netronix EC provides a PWM output, which is used for the backlight

> 

> s/,//

> 

> > on ebook readers. This patches adds a driver for the PWM output.

> 

> on *some* ebook readers


Ok, I'll fix these.

> 

> > +#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;

> 

> As you cannot use values bigger than 8191999 anyhow, I wonder why you

> use a 64 bit type here.


No particular reason; I possibly got confused by the division API. I'll
use uint32_t instead.

> > +	int res = 0;

> > +

> > +	do_div(period, 125);

> 

> Please use a define instead of plain 125.


Will do.

> > +	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;

> > +	}

> 

> This check isn't necessary as the pwm core ensures that duty <= period.


Ok, I'll remove it.
> 

> > +	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);

> 

> Does this complete the currently running period? Can it happen that a

> new period starts between the first and the last write and so a mixed

> period can be seen at the output?


Good question. I haven't measured it, and also don't have the code
running on the EC.

> 

> > +

> > +	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,

> 

> Please don't align the =, just a single space before them is fine.


Ok

> More important: Please implement .apply() (and .get_state()) instead of

> the old API. Also please enable PWM_DEBUG which might save us a review

> iteration.


Will do!

> 

> > +};

> > +

> > +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;

> 

> This is broken for several reasons:

> 

>  - You're not supposed to modify the output in .probe

>  - if ntxec_write8 results in an error you keep the pwm registered.

>  - From the moment on pwmchip_add returns the callbacks can be called.

>    The calls to ntxec_write8 probably interfere here.


Ok, I'll rework the probe function to avoid these issues.


Thanks for the review,
Jonathan Neuschäfer
diff mbox series

Patch

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@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@gmx.net>");
+MODULE_DESCRIPTION("PWM driver for Netronix EC");
+MODULE_LICENSE("GPL");