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

Uwe Kleine-König
2019-12-09T07:32:24Z

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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