linux-kernel - Re: [PATCH v2] counter: stm32-timer-cnt: add power management support

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Message-ID: <20200210174550.GA4626@icarus>
Date:   Mon, 10 Feb 2020 12:45:50 -0500
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Fabrice Gasnier <fabrice.gasnier@...com>
Cc:     jic23@...nel.org, 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 v2] counter: stm32-timer-cnt: add power management support

On Mon, Feb 10, 2020 at 06:19:58PM +0100, Fabrice Gasnier wrote:
> Add suspend/resume PM sleep ops. When going to low power, enforce the
> counter isn't active. Gracefully restore its state upon resume in case
> it's been left enabled prior to suspend.
> 
> Acked-by: William Breathitt Gray <vilhelm.gray@...il.com>
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...com>
> ---
> Changes in v2:
> - Don't refuse to suspend in case the counter has been left enabled.
>   Gracefully disable it and restore its state upon resume.
> ---
>  drivers/counter/stm32-timer-cnt.c | 63 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
> 
> diff --git a/drivers/counter/stm32-timer-cnt.c b/drivers/counter/stm32-timer-cnt.c
> index 3eafcce..50496f4 100644
> --- a/drivers/counter/stm32-timer-cnt.c
> +++ b/drivers/counter/stm32-timer-cnt.c
> @@ -12,6 +12,7 @@
>  #include <linux/iio/types.h>

Unrelated to your patch but it caught my eye: are iio headers necessary
for this file? I suspect they are not needed since this driver does not
make use of the IIO interface.

William Breathitt Gray

>  #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))
> @@ -20,11 +21,20 @@
>  #define TIM_CCER_MASK	(TIM_CCER_CC1P | TIM_CCER_CC1NP | \
>  			 TIM_CCER_CC2P | TIM_CCER_CC2NP)
>  
> +struct stm32_timer_regs {
> +	u32 cr1;
> +	u32 cnt;
> +	u32 smcr;
> +	u32 arr;
> +};
> +
>  struct stm32_timer_cnt {
>  	struct counter_device counter;
>  	struct regmap *regmap;
>  	struct clk *clk;
>  	u32 ceiling;
> +	bool enabled;
> +	struct stm32_timer_regs bak;
>  };
>  
>  /**
> @@ -224,6 +234,9 @@ static ssize_t stm32_count_enable_write(struct counter_device *counter,
>  			clk_disable(priv->clk);
>  	}
>  
> +	/* Keep enabled state to properly handle low power states */
> +	priv->enabled = enable;
> +
>  	return len;
>  }
>  
> @@ -358,10 +371,59 @@ 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);
> +
> +	/* Only take care of enabled counter: don't disturb other MFD child */
> +	if (priv->enabled) {
> +		/* Backup registers that may get lost in low power mode */
> +		regmap_read(priv->regmap, TIM_SMCR, &priv->bak.smcr);
> +		regmap_read(priv->regmap, TIM_ARR, &priv->bak.arr);
> +		regmap_read(priv->regmap, TIM_CNT, &priv->bak.cnt);
> +		regmap_read(priv->regmap, TIM_CR1, &priv->bak.cr1);
> +
> +		/* Disable the counter */
> +		regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_CEN, 0);
> +		clk_disable(priv->clk);
> +	}
> +
> +	return pinctrl_pm_select_sleep_state(dev);
> +}
> +
> +static int __maybe_unused stm32_timer_cnt_resume(struct device *dev)
> +{
> +	struct stm32_timer_cnt *priv = dev_get_drvdata(dev);
> +	int ret;
> +
> +	ret = pinctrl_pm_select_default_state(dev);
> +	if (ret)
> +		return ret;
> +
> +	if (priv->enabled) {
> +		clk_enable(priv->clk);
> +
> +		/* Restore registers that may have been lost */
> +		regmap_write(priv->regmap, TIM_SMCR, priv->bak.smcr);
> +		regmap_write(priv->regmap, TIM_ARR, priv->bak.arr);
> +		regmap_write(priv->regmap, TIM_CNT, priv->bak.cnt);
> +
> +		/* Also re-enables the counter */
> +		regmap_write(priv->regmap, TIM_CR1, priv->bak.cr1);
> +	}
> +
> +	return 0;
> +}
> +
> +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 +435,7 @@ 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);
> -- 
> 2.7.4
>