linux-kernel - Re: [PATCH] counter: stm32-timer-cnt: add power management support

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Date:   Sat, 8 Feb 2020 15:35:41 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Fabrice Gasnier <fabrice.gasnier@...com>
Cc:     <vilhelm.gray@...il.com>, <alexandre.torgue@...com>,
        <mcoquelin.stm32@...il.com>, <benjamin.gaignard@...com>,
        <linux-iio@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] counter: stm32-timer-cnt: add power management support

On Wed, 5 Feb 2020 11:47:58 +0100
Fabrice Gasnier <fabrice.gasnier@...com> wrote:

> Add suspend/resume PM sleep ops. When going to low power, enforce the
> counter isn't active.
> 
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...com>
> ---
>  drivers/counter/stm32-timer-cnt.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/drivers/counter/stm32-timer-cnt.c b/drivers/counter/stm32-timer-cnt.c
> index 3eafcce..3b84503 100644
> --- a/drivers/counter/stm32-timer-cnt.c
> +++ b/drivers/counter/stm32-timer-cnt.c
> @@ -12,6 +12,7 @@
>  #include <linux/iio/types.h>
>  #include <linux/mfd/stm32-timers.h>
>  #include <linux/module.h>
> +#include <linux/pinctrl/consumer.h>
>  #include <linux/platform_device.h>
>  
>  #define TIM_CCMR_CCXS	(BIT(8) | BIT(0))
> @@ -358,10 +359,33 @@ static int stm32_timer_cnt_probe(struct platform_device *pdev)
>  	priv->counter.num_signals = ARRAY_SIZE(stm32_signals);
>  	priv->counter.priv = priv;
>  
> +	platform_set_drvdata(pdev, priv);
> +
>  	/* Register Counter device */
>  	return devm_counter_register(dev, &priv->counter);
>  }
>  
> +static int __maybe_unused stm32_timer_cnt_suspend(struct device *dev)
> +{
> +	struct stm32_timer_cnt *priv = dev_get_drvdata(dev);
> +	u32 cr1;
> +
> +	/* Check for active counter */
> +	regmap_read(priv->regmap, TIM_CR1, &cr1);
> +	if (cr1 & TIM_CR1_CEN)
> +		return -EBUSY;

Runtime suspend is allowed to refuse to happen (and that is
explicitly documented)
Is that allowed for normal suspend?  I didn't think it was.
This will stop a suspend, but it's doing it by signalling a failure.
I'm not sure for example that the system will resume everything that
was suspended before this call.

Normally you are in the tough luck category if a system decides
to suspend underneath you.   There are ways to prevent it
from userspace (wakelocks etc).

> +
> +	return pinctrl_pm_select_sleep_state(dev);
> +}
> +
> +static int __maybe_unused stm32_timer_cnt_resume(struct device *dev)
> +{
> +	return pinctrl_pm_select_default_state(dev);
> +}
> +
> +static SIMPLE_DEV_PM_OPS(stm32_timer_cnt_pm_ops, stm32_timer_cnt_suspend,
> +			 stm32_timer_cnt_resume);
> +
>  static const struct of_device_id stm32_timer_cnt_of_match[] = {
>  	{ .compatible = "st,stm32-timer-counter", },
>  	{},
> @@ -373,6 +397,7 @@ static struct platform_driver stm32_timer_cnt_driver = {
>  	.driver = {
>  		.name = "stm32-timer-counter",
>  		.of_match_table = stm32_timer_cnt_of_match,
> +		.pm = &stm32_timer_cnt_pm_ops,
>  	},
>  };
>  module_platform_driver(stm32_timer_cnt_driver);