Message-ID: <20161205083155.GA14004@dell>
Date:   Mon, 5 Dec 2016 08:31:55 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        robh+dt@...nel.org, mark.rutland@....com, alexandre.torgue@...com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pwm@...r.kernel.org, jic23@...nel.org, knaack.h@....de,
        lars@...afoo.de, pmeerw@...erw.net, linux-iio@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, fabrice.gasnier@...com,
        gerald.baeza@...com, arnaud.pouliquen@...com,
        linus.walleij@...aro.org, linaro-kernel@...ts.linaro.org,
        Benjamin Gaignard <benjamin.gaignard@...com>
Subject: Re: [PATCH v3 4/7] PWM: add pwm driver for stm32 plaftorm

On Mon, 05 Dec 2016, Thierry Reding wrote:

> On Fri, Dec 02, 2016 at 11:17:19AM +0100, Benjamin Gaignard wrote:
> > This driver add support for pwm driver on stm32 platform.
> 
> "adds". Also please use PWM in prose because it's an abbreviation.
> 
> > The SoC have multiple instances of the hardware IP and each
> > of them could have small differences: number of channels,
> > complementary output, counter register size...
> > Use DT parameters to handle those differentes configuration
> 
> "different configurations"
> 
> > 
> > version 2:
> > - only keep one comptatible
> > - use DT paramaters to discover hardware block configuration
> 
> "parameters"
> 
> > 
> > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...com>
> > ---
> >  drivers/pwm/Kconfig     |   8 ++
> >  drivers/pwm/Makefile    |   1 +
> >  drivers/pwm/pwm-stm32.c | 285 ++++++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 294 insertions(+)
> >  create mode 100644 drivers/pwm/pwm-stm32.c
> > 
> > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> > index bf01288..a89fdba 100644
> > --- a/drivers/pwm/Kconfig
> > +++ b/drivers/pwm/Kconfig
> > @@ -388,6 +388,14 @@ config PWM_STI
> >  	  To compile this driver as a module, choose M here: the module
> >  	  will be called pwm-sti.
> >  
> > +config PWM_STM32
> > +	bool "STMicroelectronics STM32 PWM"
> > +	depends on ARCH_STM32
> > +	depends on OF
> > +	select MFD_STM32_GP_TIMER
> 
> Should that be a "depends on"?
> 
> > +	help
> > +	  Generic PWM framework driver for STM32 SoCs.
> > +
> >  config PWM_STMPE
> >  	bool "STMPE expander PWM export"
> >  	depends on MFD_STMPE
> > diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> > index 1194c54..5aa9308 100644
> > --- a/drivers/pwm/Makefile
> > +++ b/drivers/pwm/Makefile
> > @@ -37,6 +37,7 @@ obj-$(CONFIG_PWM_ROCKCHIP)	+= pwm-rockchip.o
> >  obj-$(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_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.c b/drivers/pwm/pwm-stm32.c
> > new file mode 100644
> > index 0000000..a362f63
> > --- /dev/null
> > +++ b/drivers/pwm/pwm-stm32.c
> > @@ -0,0 +1,285 @@
> > +/*
> > + * Copyright (C) STMicroelectronics 2016
> > + * Author:  Gerald Baeza <gerald.baeza@...com>
> 
> Could use a blank line between the above. Also, please use a single
> space after : for consistency.
> 
> > + * License terms:  GNU General Public License (GPL), version 2
> 
> Here too.
> 
> > + *
> > + * Inspired by timer-stm32.c from Maxime Coquelin
> > + *             pwm-atmel.c from Bo Shen
> > + */
> > +
> > +#include <linux/of.h>
> > +#include <linux/module.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/pwm.h>
> 
> Please sort these alphabetically.
> 
> > +
> > +#include <linux/mfd/stm32-gptimer.h>
> > +
> > +#define DRIVER_NAME "stm32-pwm"
> > +
> > +#define CAP_COMPLEMENTARY	BIT(0)
> > +#define CAP_32BITS_COUNTER	BIT(1)
> > +#define CAP_BREAKINPUT		BIT(2)
> > +#define CAP_BREAKINPUT_POLARITY BIT(3)
> 
> Just make these boolean. Makes the conditionals a lot simpler to read.
> 
> > +
> > +struct stm32_pwm_dev {
> 
> No need for the _dev suffix.

I usually like ddata (short for device data, which is what it is).

I'll be asking for the same in the MFD driver too.

> > +	struct device *dev;
> > +	struct clk *clk;
> > +	struct regmap *regmap;
> > +	struct pwm_chip chip;
> 
> It's slightly more efficient to put this as first field because then
> to_stm32_pwm() becomes a no-op.

Niiiice!

> > +	int caps;
> > +	int npwm;
> 
> unsigned int, please.
> 
> > +	u32 polarity;
> 
> Maybe use a prefix here to stress that it is the polarity of the
> complementary output. Otherwise one might take it for the PWM signal's
> polarity that's already part of the PWM state.
> 
> > +};
> > +
> > +#define to_stm32_pwm_dev(x) container_of(chip, struct stm32_pwm_dev, chip)
> 
> Please turn this into a static inline.
> 
> > +
> > +static u32 __active_channels(struct stm32_pwm_dev *pwm_dev)
> 
> No need for a __ prefix.
> 
> > +{
> > +	u32 ccer;
> > +
> > +	regmap_read(pwm_dev->regmap, TIM_CCER, &ccer);
> > +
> > +	return ccer & TIM_CCER_CCXE;
> > +}
> > +
> > +static int write_ccrx(struct stm32_pwm_dev *dev, struct pwm_device *pwm,
> > +		      u32 ccr)
> 
> u32 value, perhaps? I first mistook this to be a register offset.
> 
> > +{
> > +	switch (pwm->hwpwm) {
> > +	case 0:
> > +		return regmap_write(dev->regmap, TIM_CCR1, ccr);
> > +	case 1:
> > +		return regmap_write(dev->regmap, TIM_CCR2, ccr);
> > +	case 2:
> > +		return regmap_write(dev->regmap, TIM_CCR3, ccr);
> > +	case 3:
> > +		return regmap_write(dev->regmap, TIM_CCR4, ccr);
> > +	}
> > +	return -EINVAL;
> > +}
> > +
> > +static int stm32_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> > +			    int duty_ns, int period_ns)
> 
> Please implement this as an atomic PWM driver, I don't want new drivers
> to use the legacy callbacks.
> 
> > +{
> > +	struct stm32_pwm_dev *dev = to_stm32_pwm_dev(chip);
> 
> I think something like "stm", or "priv" would be more appropriate here.
> If you ever need access to a struct device, you'll be hard-pressed to
> find a good name for it.

See above.

> > +	unsigned long long prd, div, dty;
> > +	int prescaler = 0;
> 
> If this can never be negative, please make it unsigned int.
> 
> > +	u32 max_arr = 0xFFFF, ccmr, mask, shift, bdtr;
> > +
> > +	if (dev->caps & CAP_32BITS_COUNTER)
> > +		max_arr = 0xFFFFFFFF;
> 
> I prefer lower-case hexadecimal digits.

Even better to define the max values.

> > +
> > +	/* Period and prescaler values depends of clock rate */
> 
> "depend on"
> 
> > +	div = (unsigned long long)clk_get_rate(dev->clk) * period_ns;
> > +
> > +	do_div(div, NSEC_PER_SEC);
> > +	prd = div;
> > +
> > +	while (div > max_arr) {
> > +		prescaler++;
> > +		div = prd;
> > +		do_div(div, (prescaler + 1));
> > +	}
> > +	prd = div;
> 
> Blank line after blocks, please.

... unless directly related to the block, which I think this is.  It's
the '\n' *before* the block which confuses me.

> > +	if (prescaler > MAX_TIM_PSC) {
> > +		dev_err(chip->dev, "prescaler exceeds the maximum value\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	/* All channels share the same prescaler and counter so
> > +	 * when two channels are active at the same we can't change them
> > +	 */
> 
> This isn't proper block comment style. Also, please use all of the
> columns at your disposal.
> 
> > +	if (__active_channels(dev) & ~(1 << pwm->hwpwm * 4)) {
> > +		u32 psc, arr;
> > +
> > +		regmap_read(dev->regmap, TIM_PSC, &psc);
> > +		regmap_read(dev->regmap, TIM_ARR, &arr);
> > +
> > +		if ((psc != prescaler) || (arr != prd - 1))
> > +			return -EINVAL;
> 
> Maybe -EBUSY to differentiate from other error cases?
> 
> > +	}
> > +
> > +	regmap_write(dev->regmap, TIM_PSC, prescaler);
> > +	regmap_write(dev->regmap, TIM_ARR, prd - 1);
> > +	regmap_update_bits(dev->regmap, TIM_CR1, TIM_CR1_ARPE, TIM_CR1_ARPE);
> > +
> > +	/* Calculate the duty cycles */
> > +	dty = prd * duty_ns;
> > +	do_div(dty, period_ns);
> > +
> > +	write_ccrx(dev, pwm, dty);
> > +
> > +	/* Configure output mode */
> > +	shift = (pwm->hwpwm & 0x1) * 8;
> > +	ccmr = (TIM_CCMR_PE | TIM_CCMR_M1) << shift;
> > +	mask = 0xFF << shift;
> > +
> > +	if (pwm->hwpwm & 0x2)
> 
> This looks as though TIM_CCMR1 is used for channels 0 and 1, while
> TIM_CCMR2 is used for channels 2 and 3. Wouldn't it be more natural to
> make the conditional above:
> 
> 	if (pwm->hwpwm >= 2)
> 
> ? Or perhaps better yet:
> 
> 	if (pwm->hwpwm < 2)
> 		/* update TIM_CCMR1 */
> 	else
> 		/* update TIM_CCMR2 */

And please define the magic numbers.

*_MASK
*_SHIFT

> The other alternative, which might make the code slightly more readable,
> would be to get rid of all these conditionals by parameterizing the
> offsets per PWM channel. The PWM subsystem has a means of storing per-
> channel chip-specific data (see pwm_{set,get}_chip_data()). It might be
> a little overkill for this particular driver, given that the number of
> conditionals is fairly small.
> 
> > +		regmap_update_bits(dev->regmap, TIM_CCMR2, mask, ccmr);
> > +	else
> > +		regmap_update_bits(dev->regmap, TIM_CCMR1, mask, ccmr);
> > +
> > +	if (!(dev->caps & CAP_BREAKINPUT))
> > +		return 0;
> 
> If you make these capabilities boolean, it becomes much more readable,
> especially for negations:
> 
> 	if (!dev->has_breakinput)

+1

> > +
> > +	bdtr = TIM_BDTR_MOE | TIM_BDTR_AOE;
> > +
> > +	if (dev->caps & CAP_BREAKINPUT_POLARITY)
> > +		bdtr |= TIM_BDTR_BKE;
> > +
> > +	if (dev->polarity)
> > +		bdtr |= TIM_BDTR_BKP;
> > +
> > +	regmap_update_bits(dev->regmap, TIM_BDTR,
> > +			   TIM_BDTR_MOE | TIM_BDTR_AOE |
> > +			   TIM_BDTR_BKP | TIM_BDTR_BKE,
> > +			   bdtr);
> > +
> > +	return 0;
> > +}
> > +
> > +static int stm32_pwm_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm,
> > +				  enum pwm_polarity polarity)
> > +{
> > +	u32 mask;
> > +	struct stm32_pwm_dev *dev = to_stm32_pwm_dev(chip);
> > +
> > +	mask = TIM_CCER_CC1P << (pwm->hwpwm * 4);
> > +	if (dev->caps & CAP_COMPLEMENTARY)
> > +		mask |= TIM_CCER_CC1NP << (pwm->hwpwm * 4);
> > +
> > +	regmap_update_bits(dev->regmap, TIM_CCER, mask,
> > +			   polarity == PWM_POLARITY_NORMAL ? 0 : mask);
> > +
> > +	return 0;
> > +}
> > +
> > +static int stm32_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> > +{
> > +	u32 mask;
> > +	struct stm32_pwm_dev *dev = to_stm32_pwm_dev(chip);
> > +
> > +	clk_enable(dev->clk);
> > +
> > +	/* Enable channel */
> > +	mask = TIM_CCER_CC1E << (pwm->hwpwm * 4);
> > +	if (dev->caps & CAP_COMPLEMENTARY)
> > +		mask |= TIM_CCER_CC1NE << (pwm->hwpwm * 4);
> > +
> > +	regmap_update_bits(dev->regmap, TIM_CCER, mask, mask);
> > +
> > +	/* Make sure that registers are updated */
> > +	regmap_update_bits(dev->regmap, TIM_EGR, TIM_EGR_UG, TIM_EGR_UG);
> > +
> > +	/* Enable controller */
> > +	regmap_update_bits(dev->regmap, TIM_CR1, TIM_CR1_CEN, TIM_CR1_CEN);
> > +
> > +	return 0;
> > +}
> > +
> > +static void stm32_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> > +{
> > +	u32 mask;
> > +	struct stm32_pwm_dev *dev = to_stm32_pwm_dev(chip);
> > +
> > +	/* Disable channel */
> > +	mask = TIM_CCER_CC1E << (pwm->hwpwm * 4);
> > +	if (dev->caps & CAP_COMPLEMENTARY)
> > +		mask |= TIM_CCER_CC1NE << (pwm->hwpwm * 4);
> > +
> > +	regmap_update_bits(dev->regmap, TIM_CCER, mask, 0);
> > +
> > +	/* When all channels are disabled, we can disable the controller */
> > +	if (!__active_channels(dev))
> > +		regmap_update_bits(dev->regmap, TIM_CR1, TIM_CR1_CEN, 0);
> > +
> > +	clk_disable(dev->clk);
> > +}
> 
> All of the above can be folded into the ->apply() hook for atomic PWM
> support.
> 
> Also, in the above you use clk_enable() in the ->enable() callback and
> clk_disable() in ->disable(). If you need the clock to access registers
> you'll have to enabled it in the others as well because there are no
> guarantees that configuration will only happen between ->enable() and
> ->disable(). Atomic PWM simplifies this a bit, but you still need to be
> careful about when to enable the clock in your ->apply() hook.
> 
> > +
> > +static const struct pwm_ops stm32pwm_ops = {
> > +	.config = stm32_pwm_config,
> > +	.set_polarity = stm32_pwm_set_polarity,
> > +	.enable = stm32_pwm_enable,
> > +	.disable = stm32_pwm_disable,
> > +};
> 
> You need to set the .owner field as well.
> 
> > +
> > +static int stm32_pwm_probe(struct platform_device *pdev)
> > +{
> > +	struct device *dev = &pdev->dev;
> > +	struct device_node *np = dev->of_node;
> > +	struct stm32_gptimer_dev *mfd = dev_get_drvdata(pdev->dev.parent);
> > +	struct stm32_pwm_dev *pwm;

pwm is okay.  Please also consider using ddata for consistency across
the driver-set.

> > +	int ret;
> > +
> > +	pwm = devm_kzalloc(dev, sizeof(*pwm), GFP_KERNEL);
> > +	if (!pwm)
> > +		return -ENOMEM;
> > +
> > +	pwm->regmap = mfd->regmap;
> > +	pwm->clk = mfd->clk;
> > +
> > +	if (!pwm->regmap || !pwm->clk)
> > +		return -EINVAL;
> > +
> > +	if (of_property_read_bool(np, "st,complementary"))
> > +		pwm->caps |= CAP_COMPLEMENTARY;
> > +
> > +	if (of_property_read_bool(np, "st,32bits-counter"))
> > +		pwm->caps |= CAP_32BITS_COUNTER;
> > +
> > +	if (of_property_read_bool(np, "st,breakinput"))
> > +		pwm->caps |= CAP_BREAKINPUT;
> > +
> > +	if (!of_property_read_u32(np, "st,breakinput-polarity", &pwm->polarity))
> > +		pwm->caps |= CAP_BREAKINPUT_POLARITY;
> > +
> > +	of_property_read_u32(np, "st,pwm-num-chan", &pwm->npwm);
> > +
> > +	pwm->chip.base = -1;
> > +	pwm->chip.dev = dev;
> > +	pwm->chip.ops = &stm32pwm_ops;
> > +	pwm->chip.npwm = pwm->npwm;
> > +
> > +	ret = pwmchip_add(&pwm->chip);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	platform_set_drvdata(pdev, pwm);
> > +
> > +	return 0;
> > +}
> > +
> > +static int stm32_pwm_remove(struct platform_device *pdev)
> > +{
> > +	struct stm32_pwm_dev *pwm = platform_get_drvdata(pdev);
> > +	int i;
> 
> unsigned int, please.
> 
> > +
> > +	for (i = 0; i < pwm->npwm; i++)
> > +		pwm_disable(&pwm->chip.pwms[i]);
> > +
> > +	pwmchip_remove(&pwm->chip);
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct of_device_id stm32_pwm_of_match[] = {
> > +	{
> > +		.compatible = "st,stm32-pwm",
> > +	},
> 
> The above can be collapsed into a single line.

+1

> > +};
> > +MODULE_DEVICE_TABLE(of, stm32_pwm_of_match);
> > +
> > +static struct platform_driver stm32_pwm_driver = {
> > +	.probe		= stm32_pwm_probe,
> > +	.remove		= stm32_pwm_remove,
> > +	.driver	= {
> > +		.name	= DRIVER_NAME,
> > +		.of_match_table = stm32_pwm_of_match,
> > +	},
> > +};
> 
> Please don't use tabs for padding within the structure definition since
> it doesn't align properly anyway.

+1

> > +module_platform_driver(stm32_pwm_driver);
> > +
> > +MODULE_ALIAS("platform:" DRIVER_NAME);
> > +MODULE_DESCRIPTION("STMicroelectronics STM32 PWM driver");
> > +MODULE_LICENSE("GPL");
> 
> According to the header comment this should be "GPL v2".

+1



-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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