Re: [PATCH v2 2/5] pwm: Add support for the MSTAR MSC313 PWM

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

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Hello Romain, hello Daniel,

adding Mark Brown to Cc: for the regmap stuff.

On Wed, Sep 07, 2022 at 03:12:38PM +0200, Romain Perier wrote:
> From: Daniel Palmer <daniel@0x0f.com>
> 
> This adds support for the PWM block on the Mstar MSC313e SoCs and newer.
> 
> Signed-off-by: Daniel Palmer <daniel@0x0f.com>
> Co-developed-by: Romain Perier <romain.perier@gmail.com>
> Signed-off-by: Romain Perier <romain.perier@gmail.com>
> ---
>  MAINTAINERS               |   1 +
>  drivers/pwm/Kconfig       |   9 ++
>  drivers/pwm/Makefile      |   1 +
>  drivers/pwm/pwm-msc313e.c | 269 ++++++++++++++++++++++++++++++++++++++
>  4 files changed, 280 insertions(+)
>  create mode 100644 drivers/pwm/pwm-msc313e.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 9d7f64dc0efe..c3b39b09097c 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2439,6 +2439,7 @@ F:	arch/arm/mach-mstar/
>  F:	drivers/clk/mstar/
>  F:	drivers/clocksource/timer-msc313e.c
>  F:	drivers/gpio/gpio-msc313.c
> +F:	drivers/pwm/pwm-msc313e.c
>  F:	drivers/rtc/rtc-msc313.c
>  F:	drivers/watchdog/msc313e_wdt.c
>  F:	include/dt-bindings/clock/mstar-*
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 60d13a949bc5..8049fd03a821 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -372,6 +372,15 @@ config PWM_MESON
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-meson.
>  
> +config PWM_MSC313E
> +	tristate "MStar MSC313e PWM support"
> +	depends on ARCH_MSTARV7 || COMPILE_TEST
> +	help
> +	  Generic PWM framework driver for MSTAR MSC313e.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called pwm-msc313e.
> +
>  config PWM_MTK_DISP
>  	tristate "MediaTek display PWM driver"
>  	depends on ARCH_MEDIATEK || COMPILE_TEST
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index 7bf1a29f02b8..bc285c054f2a 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -62,4 +62,5 @@ 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
> +obj-$(CONFIG_PWM_MSC313E)	+= pwm-msc313e.o
>  obj-$(CONFIG_PWM_XILINX)	+= pwm-xilinx.o
> diff --git a/drivers/pwm/pwm-msc313e.c b/drivers/pwm/pwm-msc313e.c
> new file mode 100644
> index 000000000000..a71f39ba66c3
> --- /dev/null
> +++ b/drivers/pwm/pwm-msc313e.c
> @@ -0,0 +1,269 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2021 Daniel Palmer <daniel@thingy.jp>
> + * Copyright (C) 2022 Romain Perier <romain.perier@gmail.com>
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/of_device.h>
> +#include <linux/pwm.h>
> +#include <linux/regmap.h>
> +
> +#define DRIVER_NAME "msc313e-pwm"
> +
> +#define CHANNEL_OFFSET	0x80
> +#define REG_DUTY	0x8
> +#define REG_PERIOD	0x10
> +#define REG_DIV		0x18
> +#define REG_CTRL	0x1c
> +#define REG_SWRST	0x1fc
> +
> +struct msc313e_pwm_channel {
> +	struct regmap_field *clkdiv;
> +	struct regmap_field *polarity;
> +	struct regmap_field *dutyl;
> +	struct regmap_field *dutyh;
> +	struct regmap_field *periodl;
> +	struct regmap_field *periodh;
> +	struct regmap_field *swrst;
> +};
> +
> +struct msc313e_pwm {
> +	struct regmap *regmap;
> +	struct pwm_chip pwmchip;
> +	struct clk *clk;
> +	struct msc313e_pwm_channel channels[];
> +};
> +
> +struct msc313e_pwm_info {
> +	unsigned int channels;
> +};
> +
> +#define to_msc313e_pwm(ptr) container_of(ptr, struct msc313e_pwm, pwmchip)
> +
> +static const struct regmap_config msc313e_pwm_regmap_config = {
> +	.reg_bits = 16,
> +	.val_bits = 16,
> +	.reg_stride = 4,
> +};
> +
> +static const struct msc313e_pwm_info msc313e_data = {
> +	.channels = 8,
> +};
> +
> +static const struct msc313e_pwm_info ssd20xd_data = {
> +	.channels = 4,
> +};
> +
> +static void msc313e_pwm_writecounter(struct regmap_field *low, struct regmap_field *high, u32 value)
> +{
> +	/* The bus that connects the CPU to the peripheral registers splits 32 bit registers into

Please fix the comment style to use /* on a line for itself. Also for
comments staying below 80 chars per line is appreciated.

> +	 * two 16bit registers placed 4 bytes apart. It's the hardware design they used. The counter
> +	 * we are about to write has this contrainst.

s/contrainst/contraint/

I wonder if that could be abstracted by regmap?!

> +	 */
> +	regmap_field_write(low, value & 0xffff);
> +	regmap_field_write(high, value >> 16);
> +}
> +
> +static void msc313e_pwm_readcounter(struct regmap_field *low, struct regmap_field *high, u32 *value)
> +{
> +	unsigned int val = 0;
> +
> +	regmap_field_read(low, &val);
> +	*value = val;
> +	regmap_field_read(high, &val);
> +	*value = (val << 16) | *value;
> +}
> +
> +static int msc313e_pwm_config(struct pwm_chip *chip, struct pwm_device *device,
> +			      int duty_ns, int period_ns)
> +{
> +	struct msc313e_pwm *pwm = to_msc313e_pwm(chip);
> +	unsigned long long nspertick = DIV_ROUND_DOWN_ULL(NSEC_PER_SEC, clk_get_rate(pwm->clk));
> +	struct msc313e_pwm_channel *channel = &pwm->channels[device->hwpwm];
> +	unsigned long long div = 1;
> +
> +	/* Fit the period into the period register by prescaling the clk */
> +	while (DIV_ROUND_DOWN_ULL(period_ns, nspertick) > 0x3ffff) {

dividing by the result of a division looses precision. Also rounding
down both divisions looks wrong.

> +		div++;
> +		if (div > (0xffff + 1)) {
> +			/* Force clk div to the maximum allowed value */
> +			div = 0xffff;
> +			break;
> +		}
> +		nspertick = DIV_ROUND_DOWN_ULL(nspertick, div);
> +	}
> +
> +	regmap_field_write(channel->clkdiv, div - 1);
> +	msc313e_pwm_writecounter(channel->dutyl, channel->dutyh,
> +				 DIV_ROUND_DOWN_ULL(duty_ns, nspertick));
> +	msc313e_pwm_writecounter(channel->periodl, channel->periodh,
> +				 DIV_ROUND_DOWN_ULL(period_ns, nspertick));
> +	return 0;
> +};
> +
> +static int msc313e_pwm_set_polarity(struct pwm_chip *chip, struct pwm_device *device,
> +				    enum pwm_polarity polarity)
> +{
> +	struct msc313e_pwm *pwm = to_msc313e_pwm(chip);
> +	struct msc313e_pwm_channel *channel = &pwm->channels[device->hwpwm];
> +	unsigned int pol = 0;
> +
> +	if (polarity == PWM_POLARITY_INVERSED)
> +		pol = 1;
> +	regmap_field_update_bits(channel->polarity, 1, pol);
> +
> +	return 0;
> +}
> +
> +static int msc313e_pwm_enable(struct pwm_chip *chip, struct pwm_device *device)
> +{
> +	struct msc313e_pwm *pwm = to_msc313e_pwm(chip);
> +	struct msc313e_pwm_channel *channel = &pwm->channels[device->hwpwm];
> +	int ret;
> +
> +	ret = clk_prepare_enable(pwm->clk);
> +	if (ret)
> +		return ret;
> +	return regmap_field_write(channel->swrst, 0);
> +}
> +
> +static int msc313e_pwm_disable(struct pwm_chip *chip, struct pwm_device *device)
> +{
> +	struct msc313e_pwm *pwm = to_msc313e_pwm(chip);
> +	struct msc313e_pwm_channel *channel = &pwm->channels[device->hwpwm];
> +	int ret;
> +
> +	ret = regmap_field_write(channel->swrst, 1);
> +	clk_disable_unprepare(pwm->clk);
> +	return ret;
> +}
> +
> +static int msc313e_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +			 const struct pwm_state *state)
> +{
> +	int ret;
> +
> +	if (state->enabled) {
> +		if (!pwm->state.enabled) {
> +			ret = msc313e_pwm_enable(chip, pwm);
> +			if (ret)
> +				return ret;
> +		}
> +		msc313e_pwm_set_polarity(chip, pwm, state->polarity);
> +		msc313e_pwm_config(chip, pwm, state->duty_cycle, state->period);

Does the output emit a previous setting after msc313e_pwm_enable()? If
so, please do the enable at the end.

Does calling msc313e_pwm_set_polarity() and msc313e_pwm_config() have an
immediate effect? Or is the currently running period completed?

> +	} else if (pwm->state.enabled) {
> +		ret = msc313e_pwm_disable(chip, pwm);

How does the output behave on disable? Typical options are:

 - freezes where ever it currently is
 - goes to the inactive level

Does it complete the currently running period? Please answer these in a
"Limitations:" section similar to e.g. pwm-sl28cpld.c and pwm-iqs620a.

> +	}
> +	return 0;
> +}
> +
> +static void msc313e_get_state(struct pwm_chip *chip, struct pwm_device *device,

Please s/device/pwm/ to match the naming used in other drivers.

> +			      struct pwm_state *state)
> +{
> +	struct msc313e_pwm *pwm = to_msc313e_pwm(chip);
> +	struct msc313e_pwm_channel *channel = &pwm->channels[device->hwpwm];
> +	unsigned long long nspertick = DIV_ROUND_DOWN_ULL(NSEC_PER_SEC, clk_get_rate(pwm->clk));
> +	unsigned int val = 0;
> +
> +	regmap_field_read(channel->polarity, &val);
> +	state->polarity = val ? PWM_POLARITY_INVERSED : PWM_POLARITY_NORMAL;
> +
> +	regmap_field_read(channel->swrst, &val);
> +	state->enabled = val == 0 ? true : false;
> +
> +	msc313e_pwm_readcounter(channel->dutyl, channel->dutyh, &val);
> +	state->duty_cycle = val * nspertick;

Please do the division at the end. Consider val = 333335 and
clk_get_rate() returning 666666667.

Then the exact duty cycle would be 500002.49974999874 but you would
calculate nspertick = 1 and so duty_cycle = 333335.

Also you need to round up. Did you test your driver with PWM_DEBUG
enabled? The idea is that .get_state should return 500003 here to have
apply ∘ get_state idempotent. As apply is supposed to round down to the
next available setting, get_state has to round up.

> +	msc313e_pwm_readcounter(channel->periodl, channel->periodh, &val);
> +	state->period = val * nspertick;
> +}
> +
> +static const struct pwm_ops msc313e_pwm_ops = {
> +	.apply = msc313e_apply,
> +	.get_state = msc313e_get_state,
> +	.owner = THIS_MODULE
> +};
> +
> +static int msc313e_pwm_probe(struct platform_device *pdev)
> +{
> +	const struct msc313e_pwm_info *match_data;
> +	struct device *dev = &pdev->dev;
> +	struct msc313e_pwm *pwm;
> +	__iomem void *base;
> +	int i;
> +
> +	match_data = of_device_get_match_data(dev);
> +	if (!match_data)
> +		return -EINVAL;
> +
> +	base = devm_platform_ioremap_resource(pdev, 0);
> +	if (IS_ERR(base))
> +		return PTR_ERR(base);
> +
> +	pwm = devm_kzalloc(dev, struct_size(pwm, channels, match_data->channels), GFP_KERNEL);

Please don't use "pwm" as a name for your driver data variable. That
name is reserved for struct pwm_device pointers. Something like "ddata"
would be fine, but there is a wide variety in pwm driver land to choose
from.

> +	if (!pwm)
> +		return -ENOMEM;
> +
> +	pwm->clk = devm_clk_get(dev, NULL);
> +	if (IS_ERR(pwm->clk))
> +		return dev_err_probe(dev, PTR_ERR(pwm->clk), "Cannot get clk\n");
> +
> +	pwm->regmap = devm_regmap_init_mmio(dev, base, &msc313e_pwm_regmap_config);
> +	if (IS_ERR(pwm->regmap))
> +		return dev_err_probe(dev, PTR_ERR(pwm->regmap), "Cannot get regmap\n");
> +
> +	for (i = 0; i < match_data->channels; i++) {
> +		unsigned int offset = CHANNEL_OFFSET * i;
> +		struct reg_field div_clkdiv_field = REG_FIELD(offset + REG_DIV, 0, 7);
> +		struct reg_field ctrl_polarity_field = REG_FIELD(offset + REG_CTRL, 4, 4);
> +		struct reg_field dutyl_field = REG_FIELD(offset + REG_DUTY, 0, 15);
> +		struct reg_field dutyh_field = REG_FIELD(offset + REG_DUTY + 4, 0, 2);
> +		struct reg_field periodl_field = REG_FIELD(offset + REG_PERIOD, 0, 15);
> +		struct reg_field periodh_field = REG_FIELD(offset + REG_PERIOD + 4, 0, 2);
> +		struct reg_field swrst_field = REG_FIELD(REG_SWRST, i, i);
> +
> +		pwm->channels[i].clkdiv = devm_regmap_field_alloc(dev, pwm->regmap,
> +								  div_clkdiv_field);
> +		pwm->channels[i].polarity = devm_regmap_field_alloc(dev, pwm->regmap,
> +								    ctrl_polarity_field);
> +		pwm->channels[i].dutyl = devm_regmap_field_alloc(dev, pwm->regmap, dutyl_field);
> +		pwm->channels[i].dutyh = devm_regmap_field_alloc(dev, pwm->regmap, dutyh_field);
> +		pwm->channels[i].periodl = devm_regmap_field_alloc(dev, pwm->regmap, periodl_field);
> +		pwm->channels[i].periodh = devm_regmap_field_alloc(dev, pwm->regmap, periodh_field);
> +		pwm->channels[i].swrst = devm_regmap_field_alloc(dev, pwm->regmap, swrst_field);
> +
> +		/* Channels are enabled on boot, disable it until the pwm subsystem re-enable it
> +		 * explicitly

You're supposed to keep the PWM running. (Consider a bootloader setting
up a splash screen. You're probably killing the backlight here.) Note
you need improved clk handling to do that right.

> +		 */
> +		regmap_field_write(pwm->channels[i].swrst, 1);
> +	}
> +
> +	pwm->pwmchip.dev = dev;
> +	pwm->pwmchip.ops = &msc313e_pwm_ops;
> +	pwm->pwmchip.npwm = match_data->channels;
> +
> +	platform_set_drvdata(pdev, pwm);

This is unused, please drop.

> +	return devm_pwmchip_add(dev, &pwm->pwmchip);
> +}
> +
> +static const struct of_device_id msc313e_pwm_dt_ids[] = {
> +	{ .compatible = "mstar,msc313e-pwm", .data = &msc313e_data },
> +	{ .compatible = "mstar,ssd20xd-pwm", .data = &ssd20xd_data },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, msc313e_pwm_dt_ids);
> +
> +static struct platform_driver msc313e_pwm_driver = {
> +	.probe = msc313e_pwm_probe,
> +	.driver = {
> +		.name = DRIVER_NAME,
> +		.of_match_table = msc313e_pwm_dt_ids,
> +	},
> +};
> +module_platform_driver(msc313e_pwm_driver);
> +
> +MODULE_LICENSE("GPL v2");
> +MODULE_DESCRIPTION("Mstar MSC313e PWM driver");
> +MODULE_AUTHOR("Daniel Palmer <daniel@thingy.jp>");

That address doesn't match the author of this patch. Is this on purpose?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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