Subject: Re: [PATCH v2 3/3] pwm: stm32: add power management support

From: Thierry Reding <[email-masked]>
Date: Wed, 16 Oct 2019 09:06:35 +0200

On Fri, Oct 04, 2019 at 02:53:53PM +0200, Fabrice Gasnier wrote:
> Add suspend/resume PM sleep ops. When going to low power, enforce the PWM
> channel isn't active. Let the PWM consumers disable it during their own
> suspend sequence, see [1]. So, perform a check here, and handle the
> pinctrl states. Also restore the break inputs upon resume, as registers
> content may be lost when going to low power mode.
> 
> [1] https://lkml.org/lkml/2019/2/5/770
> 
> Signed-off-by: Fabrice Gasnier <[email-masked]>
> ---
> Changes in v2:
> Follow Uwe suggestions/remarks:
> - Add a precursor patch to ease reviewing
> - Use registers read instead of pwm_get_state
> - Add a comment to mention registers content may be lost in low power mode
> ---
>  drivers/pwm/pwm-stm32.c | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)

Applied, thanks. I made two minor changes, though, see below.

> 
> diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c
> index cf8658c..546b661 100644
> --- a/drivers/pwm/pwm-stm32.c
> +++ b/drivers/pwm/pwm-stm32.c
> @@ -12,6 +12,7 @@
>  #include <linux/mfd/stm32-timers.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> +#include <linux/pinctrl/consumer.h>
>  #include <linux/platform_device.h>
>  #include <linux/pwm.h>
>  
> @@ -655,6 +656,42 @@ static int stm32_pwm_remove(struct platform_device *pdev)
>  	return 0;
>  }
>  
> +static int __maybe_unused stm32_pwm_suspend(struct device *dev)
> +{
> +	struct stm32_pwm *priv = dev_get_drvdata(dev);
> +	unsigned int ch;

I renamed this to just "i", which is more idiomatic for loop variables.
The function is small enough not to need to differentiate between loop
variables.

> +	u32 ccer, mask;
> +
> +	/* Look for active channels */
> +	ccer = active_channels(priv);
> +
> +	for (ch = 0; ch < priv->chip.npwm; ch++) {
> +		mask = TIM_CCER_CC1E << (ch * 4);
> +		if (ccer & mask) {
> +			dev_err(dev, "The consumer didn't stop us (%s)\n",
> +				priv->chip.pwms[ch].label);

Changed this to:

	"PWM %u still in use by consumer %s\n", i, priv->chip.pwms[i].label

I think that might help clarify which PWM is still enabled in case the
consumers don't set a label.

Thierry

> +			return -EBUSY;
> +		}
> +	}
> +
> +	return pinctrl_pm_select_sleep_state(dev);
> +}
> +
> +static int __maybe_unused stm32_pwm_resume(struct device *dev)
> +{
> +	struct stm32_pwm *priv = dev_get_drvdata(dev);
> +	int ret;
> +
> +	ret = pinctrl_pm_select_default_state(dev);
> +	if (ret)
> +		return ret;
> +
> +	/* restore breakinput registers that may have been lost in low power */
> +	return stm32_pwm_apply_breakinputs(priv);
> +}
> +
> +static SIMPLE_DEV_PM_OPS(stm32_pwm_pm_ops, stm32_pwm_suspend, stm32_pwm_resume);
> +
>  static const struct of_device_id stm32_pwm_of_match[] = {
>  	{ .compatible = "st,stm32-pwm",	},
>  	{ /* end node */ },
> @@ -667,6 +704,7 @@ static struct platform_driver stm32_pwm_driver = {
>  	.driver	= {
>  		.name = "stm32-pwm",
>  		.of_match_table = stm32_pwm_of_match,
> +		.pm = &stm32_pwm_pm_ops,
>  	},
>  };
>  module_platform_driver(stm32_pwm_driver);
> -- 
> 2.7.4
> 
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