Message-ID: <20191106203935.fptq4lhrlfggtt2o@pengutronix.de>
Date:   Wed, 6 Nov 2019 21:39:35 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        linux-gpio@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Thierry Reding <thierry.reding@...il.com>
Subject: Re: [PATCH v2] gpio: pca953x: Add Maxim MAX7313 PWM support

Hello,

On Wed, Nov 06, 2019 at 12:26:13PM +0100, Miquel Raynal wrote:
> The MAX7313 chip is fully compatible with the PCA9535 on its basic
> functions but can also manage the intensity on each of its ports with
> PWM. Each output is independent and may be tuned with 16 values (4
> bits per output). The period is always 32kHz, only the duty-cycle may
> be changed. One can use any output as GPIO or PWM.
> 
> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> ---
> 
> Changes in v2:
> * Removed the hardcoding of PWM_CHANNELS, changed the code to use the
>   number of GPIO lines which is programatically known.
> * Used per pwm_device chip data to store the GPIO descriptors instead
>   of having a static array of GPIO descriptors in the private PWM
>   structure. It also enhanced the readability.
> * Rename an offset variable: s/off/shift/.
> * The default PWM state is now static low instead of input.
> * Used the GPIO as regular consumer thanks to the stored GPIO
>   descriptors to "make it more idiomatic" (requested by Thierry).
> * Used gpiochip_request_own_desc() instead of
>   gpio_to_desc()/gpiod_request(). This prevented the build issue and
>   an additional dependency that would have requested a DEPENDS ON line
>   in Kconfig.
> * Enhanced the return line of max7313_pwm_probe().
> 
>  drivers/gpio/gpio-pca953x.c | 236 +++++++++++++++++++++++++++++++++++-
>  1 file changed, 234 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c
> index de5d1383f28d..f90ab9e6a741 100644
> --- a/drivers/gpio/gpio-pca953x.c
> +++ b/drivers/gpio/gpio-pca953x.c
> @@ -12,18 +12,22 @@
>  #include <linux/bits.h>
>  #include <linux/gpio/driver.h>
>  #include <linux/gpio/consumer.h>
> +#include <linux/gpio/machine.h>
>  #include <linux/i2c.h>
>  #include <linux/init.h>
>  #include <linux/interrupt.h>
>  #include <linux/module.h>
>  #include <linux/of_platform.h>
>  #include <linux/platform_data/pca953x.h>
> +#include <linux/pwm.h>
>  #include <linux/regmap.h>
>  #include <linux/regulator/consumer.h>
>  #include <linux/slab.h>
>  
>  #include <asm/unaligned.h>
>  
> +#include "gpiolib.h"
> +
>  #define PCA953X_INPUT		0x00
>  #define PCA953X_OUTPUT		0x01
>  #define PCA953X_INVERT		0x02
> @@ -63,11 +67,18 @@
>  
>  #define PCA_INT			BIT(8)
>  #define PCA_PCAL		BIT(9)
> +#define MAX_PWM			BIT(10)
>  #define PCA_LATCH_INT		(PCA_PCAL | PCA_INT)
>  #define PCA953X_TYPE		BIT(12)
>  #define PCA957X_TYPE		BIT(13)
>  #define PCA_TYPE_MASK		GENMASK(15, 12)
>  
> +#define MAX7313_MASTER		0x0E
> +#define MAX7313_CONFIGURATION	0x0F
> +#define MAX7313_INTENSITY	0x10
> +
> +#define MAX7313_GLOB_INTENSITY	BIT(2)
> +
>  #define PCA_CHIP_TYPE(x)	((x) & PCA_TYPE_MASK)
>  
>  static const struct i2c_device_id pca953x_id[] = {
> @@ -93,7 +104,7 @@ static const struct i2c_device_id pca953x_id[] = {
>  
>  	{ "max7310", 8  | PCA953X_TYPE, },
>  	{ "max7312", 16 | PCA953X_TYPE | PCA_INT, },
> -	{ "max7313", 16 | PCA953X_TYPE | PCA_INT, },
> +	{ "max7313", 16 | PCA953X_TYPE | PCA_INT | MAX_PWM, },
>  	{ "max7315", 8  | PCA953X_TYPE | PCA_INT, },
>  	{ "max7318", 16 | PCA953X_TYPE | PCA_INT, },
>  	{ "pca6107", 8  | PCA953X_TYPE | PCA_INT, },
> @@ -118,6 +129,14 @@ MODULE_DEVICE_TABLE(acpi, pca953x_acpi_ids);
>  
>  #define NBANK(chip) DIV_ROUND_UP(chip->gpio_chip.ngpio, BANK_SZ)
>  
> +#define PWM_PER_REG 2
> +#define PWM_BITS_PER_REG (8 / PWM_PER_REG)
> +#define PWM_INTENSITY_MASK GENMASK(PWM_BITS_PER_REG - 1, 0)
> +
> +#define PWM_PERIOD_NS 31250
> +#define PWM_DC_STATES 16
> +#define PWM_OFFSET_NS (PWM_PERIOD_NS / PWM_DC_STATES)
> +
>  struct pca953x_reg_config {
>  	int direction;
>  	int output;
> @@ -139,6 +158,11 @@ static const struct pca953x_reg_config pca957x_regs = {
>  	.invert = PCA957X_INVRT,
>  };
>  
> +struct max7313_pwm {
> +	struct pwm_chip chip;
> +	unsigned int used;
> +};
> +
>  struct pca953x_chip {
>  	unsigned gpio_start;
>  	struct mutex i2c_lock;
> @@ -161,6 +185,8 @@ struct pca953x_chip {
>  	struct regulator *regulator;
>  
>  	const struct pca953x_reg_config *regs;
> +
> +	struct max7313_pwm pwm;
>  };
>  
>  static int pca953x_bank_shift(struct pca953x_chip *chip)
> @@ -241,8 +267,16 @@ static bool pca953x_check_register(struct pca953x_chip *chip, unsigned int reg,
>  static bool pca953x_readable_register(struct device *dev, unsigned int reg)
>  {
>  	struct pca953x_chip *chip = dev_get_drvdata(dev);
> +	unsigned int bank_sz = chip->driver_data & PCA_GPIO_MASK;
>  	u32 bank;
>  
> +	if (PCA_CHIP_TYPE(chip->driver_data) == PCA953X_TYPE &&
> +	    chip->driver_data & MAX_PWM) {
> +		if (reg >= MAX7313_MASTER &&
> +		    reg < (MAX7313_INTENSITY + bank_sz))
> +			return true;
> +	}
> +
>  	if (PCA_CHIP_TYPE(chip->driver_data) == PCA953X_TYPE) {
>  		bank = PCA953x_BANK_INPUT | PCA953x_BANK_OUTPUT |
>  		       PCA953x_BANK_POLARITY | PCA953x_BANK_CONFIG;
> @@ -264,8 +298,16 @@ static bool pca953x_readable_register(struct device *dev, unsigned int reg)
>  static bool pca953x_writeable_register(struct device *dev, unsigned int reg)
>  {
>  	struct pca953x_chip *chip = dev_get_drvdata(dev);
> +	unsigned int bank_sz = chip->driver_data & PCA_GPIO_MASK;
>  	u32 bank;
>  
> +	if (PCA_CHIP_TYPE(chip->driver_data) == PCA953X_TYPE &&
> +	    chip->driver_data & MAX_PWM) {
> +		if (reg >= MAX7313_MASTER &&
> +		    reg < (MAX7313_INTENSITY + bank_sz))
> +			return true;
> +	}
> +
>  	if (PCA_CHIP_TYPE(chip->driver_data) == PCA953X_TYPE) {
>  		bank = PCA953x_BANK_OUTPUT | PCA953x_BANK_POLARITY |
>  			PCA953x_BANK_CONFIG;
> @@ -886,6 +928,193 @@ static int device_pca957x_init(struct pca953x_chip *chip, u32 invert)
>  	return ret;
>  }
>  
> +/* PWM specific methods */
> +
> +static struct max7313_pwm *to_max7313_pwm(struct pwm_chip *chip)
> +{
> +	return container_of(chip, struct max7313_pwm, chip);
> +}
> +
> +static struct pca953x_chip *to_pca953x(struct max7313_pwm *chip)
> +{
> +	return container_of(chip, struct pca953x_chip, pwm);
> +}
> +
> +static int max7313_pwm_set_intensity(struct pca953x_chip *chip,
> +				     unsigned int idx, u8 duty_cycle)
> +{
> +	/* Duty-cycle is in the range [1;16] while registers expect [0;15] */
> +	u8 intensity = (duty_cycle - 1) & PWM_INTENSITY_MASK;
> +	unsigned int reg, shift;
> +	u8 val, mask;
> +	int ret;
> +
> +	reg = MAX7313_INTENSITY + (idx / PWM_PER_REG);
> +	shift = (idx % PWM_PER_REG) ? PWM_BITS_PER_REG : 0;
> +
> +	mask = PWM_INTENSITY_MASK << shift;
> +	val = intensity << shift;
> +
> +	mutex_lock(&chip->i2c_lock);
> +	ret = regmap_write_bits(chip->regmap, reg, mask, val);
> +	mutex_unlock(&chip->i2c_lock);
> +
> +	return ret;
> +}
> +
> +/*
> + * For a given PWM channel, when the blink phase 0 bit is set, the intensity
> + * range is only [1/16;16/16]. With this range, a static low output is
> + * physically not possible. When the blink phase 0 bit is cleared, the intensity
> + * range is [15/16;0/16] which then allows a static low output but not a static
> + * high output.
> + *
> + * In this driver we choose to set the blink phase 0 bit by default, hence we
> + * can slide from a low output to a fully high output without glitch. However,
> + * the only way to get a static low output is by clearing the blink phase 0 bit,
> + * and by changing the intensity value to its maximum (as, at this moment,
> + * intensity is reversed). There is no way to atomically flip the register *and*
> + * change the PWM value at the same time so this will produce a small glitch.
> + */
> +static int max7313_pwm_set_state(struct pca953x_chip *chip,
> +				 struct pwm_device *pwm_device,
> +				 unsigned int duty_cycle)
> +{
> +	int ret;
> +
> +	/* A null duty_cycle will invert the phase */
> +	ret = gpiod_direction_output(pwm_get_chip_data(pwm_device), duty_cycle);
> +	if (ret)
> +		return ret;
> +
> +	/* Maximize the low time in case of static low state */
> +	if (!duty_cycle)
> +		duty_cycle = PWM_DC_STATES;
> +
> +	return max7313_pwm_set_intensity(chip, pwm_device->hwpwm, duty_cycle);
> +}
> +
> +static int max7313_pwm_request(struct pwm_chip *pwm_chip,
> +			       struct pwm_device *pwm_device)
> +{
> +	struct gpio_desc *desc = pwm_get_chip_data(pwm_device);
> +	struct max7313_pwm *pwm = to_max7313_pwm(pwm_chip);
> +	struct pca953x_chip *chip = to_pca953x(pwm);
> +	int ret;
> +
> +	if (desc)
> +		return -EBUSY;
> +
> +	desc = gpiochip_request_own_desc(&chip->gpio_chip, pwm_device->hwpwm,
> +					 "max7313-pwm", GPIO_ACTIVE_HIGH,
> +					 GPIOD_OUT_LOW);
> +	if (IS_ERR(desc))
> +		return PTR_ERR(desc);

Would it make sense to add an error message here?

> +	pwm_set_chip_data(pwm_device, desc);
> +
> +	ret = max7313_pwm_set_state(chip, pwm_device, 0);
> +	if (ret)
> +		goto free_gpiod;

And here?

> +
> +	/*
> +	 * Set master intensity to the maximum level to let individual outputs
> +	 * the greatest flexibility range. Also enables the internal oscillator.
> +	 */
> +	if (!pwm->used) {
> +		mutex_lock(&chip->i2c_lock);
> +		ret = regmap_write_bits(chip->regmap, MAX7313_MASTER,
> +					PWM_INTENSITY_MASK << PWM_BITS_PER_REG,
> +					PWM_INTENSITY_MASK << PWM_BITS_PER_REG);
> +		mutex_unlock(&chip->i2c_lock);
> +		if (ret)
> +			goto free_gpiod;
> +	}
> +
> +	pwm->used++;
> +
> +	return 0;
> +
> +free_gpiod:
> +	gpiochip_free_own_desc(desc);
> +	pwm_set_chip_data(pwm_device, NULL);
> +
> +	return ret;
> +}
> +
> +static void max7313_pwm_free(struct pwm_chip *pwm_chip,
> +			     struct pwm_device *pwm_device)
> +{
> +	struct gpio_desc *desc = pwm_get_chip_data(pwm_device);
> +	struct max7313_pwm *pwm = to_max7313_pwm(pwm_chip);
> +	struct pca953x_chip *chip = to_pca953x(pwm);
> +
> +	max7313_pwm_set_state(chip, pwm_device, 0);
> +	pwm->used--;
> +
> +	/* Disable the internal oscillator if no channel is in use */
> +	if (!pwm->used) {
> +		mutex_lock(&chip->i2c_lock);
> +		regmap_write_bits(chip->regmap, MAX7313_MASTER,
> +				  PWM_INTENSITY_MASK << PWM_BITS_PER_REG, 0);
> +		mutex_unlock(&chip->i2c_lock);
> +	}

This might race against max7313_pwm_request(). Consider .used being 1.

	CPU 1						CPU2

	in max7313_pwm_request() checks
	pwm->used, sees it being 1 and so doesn't
	set intensity

							in max7313_pwm_free() decreases
							pwm->used to 0 and so unsets
							max intensity

        pwm->used++;


> +	gpiochip_free_own_desc(desc);
> +	pwm_set_chip_data(pwm_device, NULL);
> +}
> +
> +static int max7313_pwm_apply(struct pwm_chip *pwm_chip,
> +			     struct pwm_device *pwm_device,
> +			     const struct pwm_state *state)
> +{
> +	struct max7313_pwm *pwm = to_max7313_pwm(pwm_chip);
> +	struct pca953x_chip *chip = to_pca953x(pwm);
> +	unsigned int duty_cycle;
> +
> +	if (!state->enabled || !state->period || !state->duty_cycle)

!state->period cannot happen.

> +		duty_cycle = 0;
> +	else
> +		/* Convert the duty-cycle to be in the [1;16] range */
> +		duty_cycle = DIV_ROUND_UP(state->duty_cycle * PWM_DC_STATES,
> +					  state->period);

Also it seems the PWM's period (31250 ns) is fixed and unchecked here. Please
refuse requests with .period < 31250 and try to implement .duty_cycle instead
of proportions. (Also please round down duty_cycle instead of up.)

> +	return max7313_pwm_set_state(chip, pwm_device, duty_cycle);

Does changing the duty_cycle complete the currently running period?

> +}

You need to check for state->polarity, too.

> +static const struct pwm_ops max7313_pwm_ops = {
> +	.request = max7313_pwm_request,
> +	.free = max7313_pwm_free,
> +	.apply = max7313_pwm_apply,

Please implement .get_state().

> +	.owner = THIS_MODULE,
> +};
> +
> +static int max7313_pwm_probe(struct device *dev,
> +			     struct pca953x_chip *chip)
> +{
> +	struct max7313_pwm *pwm = &chip->pwm;
> +	struct pwm_chip *pwm_chip = &pwm->chip;
> +	int ret;
> +
> +	if (!(chip->driver_data & MAX_PWM))
> +		return 0;
> +
> +	pwm_chip->dev = dev;
> +	pwm_chip->ops = &max7313_pwm_ops;
> +	pwm_chip->npwm = chip->gpio_chip.ngpio;
> +	pwm_chip->base = -1;
> +
> +	/* Disable global control */
> +	mutex_lock(&chip->i2c_lock);
> +	ret = regmap_write_bits(chip->regmap, MAX7313_CONFIGURATION,
> +				MAX7313_GLOB_INTENSITY, 0);

Does this affect the gpio functionality?

> +	mutex_unlock(&chip->i2c_lock);
> +	if (ret)
> +		return ret;
> +
> +	return pwmchip_add(pwm_chip);
> +}
> +
>  static const struct of_device_id pca953x_dt_ids[];
>  
>  static int pca953x_probe(struct i2c_client *client,
> @@ -1018,6 +1247,9 @@ static int pca953x_probe(struct i2c_client *client,
>  			dev_warn(&client->dev, "setup failed, %d\n", ret);
>  	}
>  
> +	if (IS_ENABLED(CONFIG_PWM))
> +		return max7313_pwm_probe(&client->dev, chip);
> +
>  	return 0;
>  
>  err_exit:
> @@ -1162,7 +1394,7 @@ static const struct of_device_id pca953x_dt_ids[] = {
>  
>  	{ .compatible = "maxim,max7310", .data = OF_953X( 8, 0), },
>  	{ .compatible = "maxim,max7312", .data = OF_953X(16, PCA_INT), },
> -	{ .compatible = "maxim,max7313", .data = OF_953X(16, PCA_INT), },
> +	{ .compatible = "maxim,max7313", .data = OF_953X(16, PCA_INT | MAX_PWM), },
>  	{ .compatible = "maxim,max7315", .data = OF_953X( 8, PCA_INT), },
>  	{ .compatible = "maxim,max7318", .data = OF_953X(16, PCA_INT), },
>  
> -- 
> 2.20.1
> 
> 

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

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