Re: [PATCH v2 4/7] pwm: Add support for Azoteq IQS620A PWM generator

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

On Mon, Dec 09, 2019 at 12:38:36AM +0000, Jeff LaBundy wrote:
> This patch adds support for the Azoteq IQS620A, capable of generating
> a 1-kHz PWM output with duty cycle between 0.4% and 100% (inclusive).
> 
> Signed-off-by: Jeff LaBundy <jeff@labundy.com>
> ---
> Changes in v2:
>   - Merged 'Copyright' and 'Author' lines into one in introductory comments
>   - Added 'Limitations' section to introductory comments
>   - Replaced 'error' with 'ret' throughout
>   - Added const qualifier to state argument of iqs620_pwm_apply and removed all
>     modifications to the variable's contents
>   - Updated iqs620_pwm_apply to return -ENOTSUPP or -EINVAL if the requested
>     polarity is inverted or the requested period is below 1 ms, respectively
>   - Updated iqs620_pwm_apply to disable the PWM output if duty cycle is zero
>   - Added iqs620_pwm_get_state
>   - Eliminated tabbed alignment of pwm_ops and platform_driver struct members
>   - Moved notifier unregistration to already present iqs620_pwm_remove, which
>     eliminated the need for a device-managed action and ready flag
>   - Added a comment in iqs620_pwm_probe to explain the order of operations
>   - Changed Kconfig "depends on" logic to MFD_IQS62X || COMPILE_TEST
> 
>  drivers/pwm/Kconfig       |  10 +++
>  drivers/pwm/Makefile      |   1 +
>  drivers/pwm/pwm-iqs620a.c | 206 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 217 insertions(+)
>  create mode 100644 drivers/pwm/pwm-iqs620a.c
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index bd21655..60bcf6c 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -222,6 +222,16 @@ config PWM_IMX_TPM
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-imx-tpm.
> 
> +config PWM_IQS620A
> +	tristate "Azoteq IQS620A PWM support"
> +	depends on MFD_IQS62X || COMPILE_TEST
> +	help
> +	  Generic PWM framework driver for the Azoteq IQS620A multi-function
> +	  sensor.
> +
> +	  To compile this driver as a module, choose M here: the module will
> +	  be called pwm-iqs620a.
> +
>  config PWM_JZ4740
>  	tristate "Ingenic JZ47xx PWM support"
>  	depends on MACH_INGENIC
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index 9a47507..a59c710 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -20,6 +20,7 @@ obj-$(CONFIG_PWM_IMG)		+= pwm-img.o
>  obj-$(CONFIG_PWM_IMX1)		+= pwm-imx1.o
>  obj-$(CONFIG_PWM_IMX27)		+= pwm-imx27.o
>  obj-$(CONFIG_PWM_IMX_TPM)	+= pwm-imx-tpm.o
> +obj-$(CONFIG_PWM_IQS620A)	+= pwm-iqs620a.o
>  obj-$(CONFIG_PWM_JZ4740)	+= pwm-jz4740.o
>  obj-$(CONFIG_PWM_LP3943)	+= pwm-lp3943.o
>  obj-$(CONFIG_PWM_LPC18XX_SCT)	+= pwm-lpc18xx-sct.o
> diff --git a/drivers/pwm/pwm-iqs620a.c b/drivers/pwm/pwm-iqs620a.c
> new file mode 100644
> index 0000000..1ea11b9
> --- /dev/null
> +++ b/drivers/pwm/pwm-iqs620a.c
> @@ -0,0 +1,206 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Azoteq IQS620A PWM Generator
> + *
> + * Copyright (C) 2019 Jeff LaBundy <jeff@labundy.com>
> + *
> + * Limitations:
> + * - The period is not guaranteed to run to completion when the duty cycle is
> + *   changed or the output is disabled.

Do you know more details here? "not guaranteed" means that the new
period starts immediately when duty_cycle or the enabled bit is written?

> + * - The period is fixed to 1 ms.
> + */
> +
> +#include <linux/device.h>
> +#include <linux/kernel.h>
> +#include <linux/mfd/iqs62x.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +#include <linux/regmap.h>
> +#include <linux/slab.h>
> +
> +#define IQS620_PWR_SETTINGS			0xD2
> +#define IQS620_PWR_SETTINGS_PWM_OUT		BIT(7)
> +
> +#define IQS620_PWM_DUTY_CYCLE			0xD8
> +
> +#define IQS620_PWM_PERIOD_NS			1000000
> +
> +struct iqs620_pwm_private {
> +	struct iqs62x_core *iqs62x;
> +	struct pwm_chip chip;
> +	struct notifier_block notifier;
> +};
> +
> +static int iqs620_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +			    const struct pwm_state *state)
> +{
> +	struct iqs620_pwm_private *iqs620_pwm;
> +	struct iqs62x_core *iqs62x;
> +	unsigned int pwm_out = 0;
> +	int duty_scale, ret;
> +
> +	if (state->polarity != PWM_POLARITY_NORMAL)
> +		return -ENOTSUPP;
> +
> +	if (state->period < IQS620_PWM_PERIOD_NS)
> +		return -EINVAL;
> +
> +	iqs620_pwm = container_of(chip, struct iqs620_pwm_private, chip);
> +	iqs62x = iqs620_pwm->iqs62x;
> +
> +	duty_scale = DIV_ROUND_CLOSEST(state->duty_cycle * 256,
> +				       IQS620_PWM_PERIOD_NS);
> +
> +	if (duty_scale) {
> +		ret = regmap_write(iqs62x->map, IQS620_PWM_DUTY_CYCLE,
> +				   min(duty_scale - 1, 0xFF));
> +		if (ret)
> +			return ret;
> +
> +		if (state->enabled)
> +			pwm_out = IQS620_PWR_SETTINGS_PWM_OUT;
> +	}
> +
> +	return regmap_update_bits(iqs62x->map, IQS620_PWR_SETTINGS,
> +				  IQS620_PWR_SETTINGS_PWM_OUT, pwm_out);

A comment explaining the semantic here would be good. I assume
IQS620_PWM_DUTY_CYCLE takes a value between 0 and 255 and the resulting
duty cycle is:

	(IQS620_PWM_DUTY_CYCLE + 1) / 256 * 1 ms

.

If this is right, please use:

	duty_scale = (state->duty_cycle * 256) / IQS620_PWM_PERIOD_NS

Also, when the hardware is running at

	.enabled = 1, .duty_cycle = 1/256 ms, .period = 1ms

and you reconfigure to

	.enabled = 0, .duty_cycle = 1ms, .period = 1ms

the output might be active for > 1/256 ms if the process is preempted
between writing IQS620_PWM_DUTY_CYCLE and IQS620_PWR_SETTINGS_PWM_OUT.

> +}
> +
> +static void iqs620_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> +				 struct pwm_state *state)
> +{
> +	struct iqs620_pwm_private *iqs620_pwm;
> +	struct iqs62x_core *iqs62x;
> +	unsigned int val;
> +	int ret;
> +
> +	iqs620_pwm = container_of(chip, struct iqs620_pwm_private, chip);
> +	iqs62x = iqs620_pwm->iqs62x;
> +
> +	ret = regmap_read(iqs62x->map, IQS620_PWR_SETTINGS, &val);
> +	if (ret)
> +		goto err_out;
> +	state->enabled = val & IQS620_PWR_SETTINGS_PWM_OUT;
> +
> +	ret = regmap_read(iqs62x->map, IQS620_PWM_DUTY_CYCLE, &val);
> +	if (ret)
> +		goto err_out;
> +	state->duty_cycle = DIV_ROUND_CLOSEST((val + 1) * IQS620_PWM_PERIOD_NS,
> +					      256);

Please round up.

> +	state->period = IQS620_PWM_PERIOD_NS;
> +
> +err_out:
> +	if (ret)
> +		dev_err(iqs620_pwm->chip.dev, "Failed to get state: %d\n", ret);
> +}
> +
> +static int iqs620_pwm_notifier(struct notifier_block *notifier,
> +			       unsigned long event_flags, void *context)
> +{
> +	struct iqs620_pwm_private *iqs620_pwm;
> +	struct pwm_state state;
> +	int ret;
> +
> +	if (!(event_flags & BIT(IQS62X_EVENT_SYS_RESET)))
> +		return NOTIFY_DONE;
> +
> +	iqs620_pwm = container_of(notifier, struct iqs620_pwm_private,
> +				  notifier);
> +	pwm_get_state(&iqs620_pwm->chip.pwms[0], &state);

Please don't call pwm API functions in callbacks. I assume you rely on
pwm_get_state returning the previously set state and that
iqs620_pwm_get_state isn't called. Please use pwm->state for that.

> +	ret = iqs620_pwm_apply(&iqs620_pwm->chip,
> +			       &iqs620_pwm->chip.pwms[0], &state);
> +	if (ret) {
> +		dev_err(iqs620_pwm->chip.dev,
> +			"Failed to re-initialize device: %d\n", ret);
> +		return NOTIFY_BAD;
> +	}
> +
> +	return NOTIFY_OK;
> +}
> +
> +static const struct pwm_ops iqs620_pwm_ops = {
> +	.apply = iqs620_pwm_apply,
> +	.get_state = iqs620_pwm_get_state,
> +	.owner = THIS_MODULE,
> +};
> +
> +static int iqs620_pwm_probe(struct platform_device *pdev)
> +{
> +	struct iqs620_pwm_private *iqs620_pwm;
> +	int ret1, ret2;
> +
> +	iqs620_pwm = devm_kzalloc(&pdev->dev, sizeof(*iqs620_pwm), GFP_KERNEL);
> +	if (!iqs620_pwm)
> +		return -ENOMEM;
> +
> +	platform_set_drvdata(pdev, iqs620_pwm);
> +	iqs620_pwm->iqs62x = dev_get_drvdata(pdev->dev.parent);
> +
> +	iqs620_pwm->chip.dev = &pdev->dev;
> +	iqs620_pwm->chip.ops = &iqs620_pwm_ops;
> +	iqs620_pwm->chip.base = -1;
> +	iqs620_pwm->chip.npwm = 1;
> +
> +	ret1 = pwmchip_add(&iqs620_pwm->chip);
> +	if (ret1) {
> +		dev_err(&pdev->dev, "Failed to add device: %d\n", ret1);
> +		return ret1;
> +	}
> +
> +	/*
> +	 * Since iqs620_pwm_notifier uses iqs620_pwm->chip.pwms[], the notifier
> +	 * is not registered until pwmchip_add (which allocates that array) has
> +	 * been called. If registration fails, the newly added device has to be
> +	 * removed because the driver fails to probe and iqs620_pwm_remove will
> +	 * never be called.
> +	 */
> +	iqs620_pwm->notifier.notifier_call = iqs620_pwm_notifier;
> +	ret1 = blocking_notifier_chain_register(&iqs620_pwm->iqs62x->nh,
> +						&iqs620_pwm->notifier);
> +	if (ret1) {
> +		dev_err(&pdev->dev, "Failed to register notifier: %d\n", ret1);
> +
> +		ret2 = pwmchip_remove(&iqs620_pwm->chip);
> +		if (ret2) {
> +			dev_err(&pdev->dev, "Failed to remove device: %d\n",
> +				ret2);
> +			return ret2;

This exitpoint is bad. The PWM driver is active but the module gets
unloaded. I liked the approach from v1 better.

ret2 could be local to this block.

> +		}
> +	}
> +
> +	return ret1;
> +}

Best regards
Uwe

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Pengutronix e.K.                           | Uwe Kleine-König            |
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