Re: [PATCH v3 4/9] pwm: Add STM32 LPTimer PWM driver

[Fabrice Gasnier <fabrice.gasnier@st.com>]

On 07/07/2017 06:31 PM, Fabrice Gasnier wrote:
> Add support for single PWM channel on Low-Power Timer, that can be
> found on some STM32 platforms.
> 
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
> ---
> Changes in v3:
> - remove prescalers[] array, use power-of-2 presc directly
> - Update following Thierry's comments:
> - fix issue using FIELD_GET() macro
> - Add get_state() callback
> - remove some checks in probe
> - slight rework 'reenable' flag
> - use more common method to disable pwm in remove()

Hi Thierry,

Gentle ping for PWM driver review since I did changes in v3.
Please advise.

Best Regards,
Fabrice
> 
> Changes in v2:
> - s/Low Power/Low-Power
> - update few comment lines
> ---
>  drivers/pwm/Kconfig        |  10 ++
>  drivers/pwm/Makefile       |   1 +
>  drivers/pwm/pwm-stm32-lp.c | 246 +++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 257 insertions(+)
>  create mode 100644 drivers/pwm/pwm-stm32-lp.c
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 313c107..7cb982b 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -417,6 +417,16 @@ config PWM_STM32
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-stm32.
>  
> +config PWM_STM32_LP
> +	tristate "STMicroelectronics STM32 PWM LP"
> +	depends on MFD_STM32_LPTIMER || COMPILE_TEST
> +	help
> +	  Generic PWM framework driver for STMicroelectronics STM32 SoCs
> +	  with Low-Power Timer (LPTIM).
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called pwm-stm32-lp.
> +
>  config PWM_STMPE
>  	bool "STMPE expander PWM export"
>  	depends on MFD_STMPE
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index 93da1f7..a3a4bee 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -40,6 +40,7 @@ obj-$(CONFIG_PWM_SAMSUNG)	+= pwm-samsung.o
>  obj-$(CONFIG_PWM_SPEAR)		+= pwm-spear.o
>  obj-$(CONFIG_PWM_STI)		+= pwm-sti.o
>  obj-$(CONFIG_PWM_STM32)		+= pwm-stm32.o
> +obj-$(CONFIG_PWM_STM32_LP)	+= pwm-stm32-lp.o
>  obj-$(CONFIG_PWM_STMPE)		+= pwm-stmpe.o
>  obj-$(CONFIG_PWM_SUN4I)		+= pwm-sun4i.o
>  obj-$(CONFIG_PWM_TEGRA)		+= pwm-tegra.o
> diff --git a/drivers/pwm/pwm-stm32-lp.c b/drivers/pwm/pwm-stm32-lp.c
> new file mode 100644
> index 0000000..9793b29
> --- /dev/null
> +++ b/drivers/pwm/pwm-stm32-lp.c
> @@ -0,0 +1,246 @@
> +/*
> + * STM32 Low-Power Timer PWM driver
> + *
> + * Copyright (C) STMicroelectronics 2017
> + *
> + * Author: Gerald Baeza <gerald.baeza@st.com>
> + *
> + * License terms: GNU General Public License (GPL), version 2
> + *
> + * Inspired by Gerald Baeza's pwm-stm32 driver
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/mfd/stm32-lptimer.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +
> +struct stm32_pwm_lp {
> +	struct pwm_chip chip;
> +	struct clk *clk;
> +	struct regmap *regmap;
> +};
> +
> +static inline struct stm32_pwm_lp *to_stm32_pwm_lp(struct pwm_chip *chip)
> +{
> +	return container_of(chip, struct stm32_pwm_lp, chip);
> +}
> +
> +/* STM32 Low-Power Timer is preceded by a configurable power-of-2 prescaler */
> +#define STM32_LPTIM_MAX_PRESCALER	128
> +
> +static int stm32_pwm_lp_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +			      struct pwm_state *state)
> +{
> +	struct stm32_pwm_lp *priv = to_stm32_pwm_lp(chip);
> +	unsigned long long prd, div, dty;
> +	struct pwm_state cstate;
> +	u32 val, mask, cfgr, presc = 0;
> +	bool reenable;
> +	int ret;
> +
> +	pwm_get_state(pwm, &cstate);
> +	reenable = !cstate.enabled;
> +
> +	if (!state->enabled) {
> +		if (cstate.enabled) {
> +			/* Disable LP timer */
> +			ret = regmap_write(priv->regmap, STM32_LPTIM_CR, 0);
> +			if (ret)
> +				return ret;
> +			/* disable clock to PWM counter */
> +			clk_disable(priv->clk);
> +		}
> +		return 0;
> +	}
> +
> +	/* Calculate the period and prescaler value */
> +	div = (unsigned long long)clk_get_rate(priv->clk) * state->period;
> +	do_div(div, NSEC_PER_SEC);
> +	prd = div;
> +	while (div > STM32_LPTIM_MAX_ARR) {
> +		presc++;
> +		if ((1 << presc) > STM32_LPTIM_MAX_PRESCALER) {
> +			dev_err(priv->chip.dev, "max prescaler exceeded\n");
> +			return -EINVAL;
> +		}
> +		div = prd >> presc;
> +	}
> +	prd = div;
> +
> +	/* Calculate the duty cycle */
> +	dty = prd * state->duty_cycle;
> +	do_div(dty, state->period);
> +
> +	if (!cstate.enabled) {
> +		/* enable clock to drive PWM counter */
> +		ret = clk_enable(priv->clk);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	ret = regmap_read(priv->regmap, STM32_LPTIM_CFGR, &cfgr);
> +	if (ret)
> +		goto err;
> +
> +	if ((FIELD_GET(STM32_LPTIM_PRESC, cfgr) != presc) ||
> +	    (FIELD_GET(STM32_LPTIM_WAVPOL, cfgr) != state->polarity)) {
> +		val = FIELD_PREP(STM32_LPTIM_PRESC, presc);
> +		val |= FIELD_PREP(STM32_LPTIM_WAVPOL, state->polarity);
> +		mask = STM32_LPTIM_PRESC | STM32_LPTIM_WAVPOL;
> +
> +		/* Must disable LP timer to modify CFGR */
> +		reenable = true;
> +		ret = regmap_write(priv->regmap, STM32_LPTIM_CR, 0);
> +		if (ret)
> +			goto err;
> +
> +		ret = regmap_update_bits(priv->regmap, STM32_LPTIM_CFGR, mask,
> +					 val);
> +		if (ret)
> +			goto err;
> +	}
> +
> +	if (reenable) {
> +		/* Must (re)enable LP timer to modify CMP & ARR */
> +		ret = regmap_write(priv->regmap, STM32_LPTIM_CR,
> +				   STM32_LPTIM_ENABLE);
> +		if (ret)
> +			goto err;
> +	}
> +
> +	ret = regmap_write(priv->regmap, STM32_LPTIM_ARR, prd - 1);
> +	if (ret)
> +		goto err;
> +
> +	ret = regmap_write(priv->regmap, STM32_LPTIM_CMP, prd - (1 + dty));
> +	if (ret)
> +		goto err;
> +
> +	/* ensure CMP & ARR registers are properly written */
> +	ret = regmap_read_poll_timeout(priv->regmap, STM32_LPTIM_ISR, val,
> +				       (val & STM32_LPTIM_CMPOK_ARROK),
> +				       100, 1000);
> +	if (ret) {
> +		dev_err(priv->chip.dev, "ARR/CMP registers write issue\n");
> +		goto err;
> +	}
> +	ret = regmap_write(priv->regmap, STM32_LPTIM_ICR,
> +			   STM32_LPTIM_CMPOKCF_ARROKCF);
> +	if (ret)
> +		goto err;
> +
> +	if (reenable) {
> +		/* Start LP timer in continuous mode */
> +		ret = regmap_update_bits(priv->regmap, STM32_LPTIM_CR,
> +					 STM32_LPTIM_CNTSTRT,
> +					 STM32_LPTIM_CNTSTRT);
> +		if (ret) {
> +			regmap_write(priv->regmap, STM32_LPTIM_CR, 0);
> +			goto err;
> +		}
> +	}
> +
> +	return 0;
> +err:
> +	if (!cstate.enabled)
> +		clk_disable(priv->clk);
> +
> +	return ret;
> +}
> +
> +static void stm32_pwm_lp_get_state(struct pwm_chip *chip,
> +				   struct pwm_device *pwm,
> +				   struct pwm_state *state)
> +{
> +	struct stm32_pwm_lp *priv = to_stm32_pwm_lp(chip);
> +	unsigned long rate = clk_get_rate(priv->clk);
> +	u32 val, presc, prd;
> +	u64 tmp;
> +
> +	regmap_read(priv->regmap, STM32_LPTIM_CR, &val);
> +	state->enabled = !!FIELD_GET(STM32_LPTIM_ENABLE, val);
> +	/* Keep PWM counter clock refcount in sync with PWM initial state */
> +	if (state->enabled)
> +		clk_enable(priv->clk);
> +
> +	regmap_read(priv->regmap, STM32_LPTIM_CFGR, &val);
> +	presc = FIELD_GET(STM32_LPTIM_PRESC, val);
> +	state->polarity = FIELD_GET(STM32_LPTIM_WAVPOL, val);
> +
> +	regmap_read(priv->regmap, STM32_LPTIM_ARR, &prd);
> +	tmp = prd + 1;
> +	tmp = (tmp << presc) * NSEC_PER_SEC;
> +	state->period = DIV_ROUND_CLOSEST_ULL(tmp, rate);
> +
> +	regmap_read(priv->regmap, STM32_LPTIM_CMP, &val);
> +	tmp = prd - val;
> +	tmp = (tmp << presc) * NSEC_PER_SEC;
> +	state->duty_cycle = DIV_ROUND_CLOSEST_ULL(tmp, rate);
> +}
> +
> +static const struct pwm_ops stm32_pwm_lp_ops = {
> +	.owner = THIS_MODULE,
> +	.apply = stm32_pwm_lp_apply,
> +	.get_state = stm32_pwm_lp_get_state,
> +};
> +
> +static int stm32_pwm_lp_probe(struct platform_device *pdev)
> +{
> +	struct stm32_lptimer *ddata = dev_get_drvdata(pdev->dev.parent);
> +	struct stm32_pwm_lp *priv;
> +	int ret;
> +
> +	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	priv->regmap = ddata->regmap;
> +	priv->clk = ddata->clk;
> +	priv->chip.base = -1;
> +	priv->chip.dev = &pdev->dev;
> +	priv->chip.ops = &stm32_pwm_lp_ops;
> +	priv->chip.npwm = 1;
> +
> +	ret = pwmchip_add(&priv->chip);
> +	if (ret < 0)
> +		return ret;
> +
> +	platform_set_drvdata(pdev, priv);
> +
> +	return 0;
> +}
> +
> +static int stm32_pwm_lp_remove(struct platform_device *pdev)
> +{
> +	struct stm32_pwm_lp *priv = platform_get_drvdata(pdev);
> +	unsigned int i;
> +
> +	for (i = 0; i < priv->chip.npwm; i++)
> +		if (pwm_is_enabled(&priv->chip.pwms[i]))
> +			pwm_disable(&priv->chip.pwms[i]);
> +
> +	return pwmchip_remove(&priv->chip);
> +}
> +
> +static const struct of_device_id stm32_pwm_lp_of_match[] = {
> +	{ .compatible = "st,stm32-pwm-lp", },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, stm32_pwm_lp_of_match);
> +
> +static struct platform_driver stm32_pwm_lp_driver = {
> +	.probe	= stm32_pwm_lp_probe,
> +	.remove	= stm32_pwm_lp_remove,
> +	.driver	= {
> +		.name = "stm32-pwm-lp",
> +		.of_match_table = of_match_ptr(stm32_pwm_lp_of_match),
> +	},
> +};
> +module_platform_driver(stm32_pwm_lp_driver);
> +
> +MODULE_ALIAS("platform:stm32-pwm-lp");
> +MODULE_DESCRIPTION("STMicroelectronics STM32 PWM LP driver");
> +MODULE_LICENSE("GPL v2");
>