linux-kernel - Re: [PATCH] drivers/clocksource/timer-ti-dm: Don't call clk_get

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Message-ID: <ZaK5wOHxf2CvzZrk@gofer.mess.org>
Date: Sat, 13 Jan 2024 16:26:40 +0000
From: Sean Young <sean@...s.org>
To: Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
Cc: daniel.lezcano@...aro.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, tony@...mide.com,
	linux-pwm@...r.kernel.org
Subject: Re: [PATCH] drivers/clocksource/timer-ti-dm: Don't call
 clk_get_rate() in stop function

Hi Ivaylo,

On Tue, Oct 03, 2023 at 08:50:20AM +0300, Ivaylo Dimitrov wrote:
> clk_get_rate() might sleep, and that prevents dm-timer based PWM from being
> used from atomic context.

Now that this is merged, pwm-ir-tx can only use the pwm in atomic context
if pwm-omap-timer.c sets the atomic field like the rpi pwm does here:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pwm/pwm-bcm2835.c#n175

see pwm-ir-tx here:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/media/rc/pwm-ir-tx.c#n170

It would be nice to have this tested and working properly for the n900.

Thanks,

Sean


> 
> Fix that by getting fclk rate in probe() and using a notifier in case rate
> changes.
> 
> Fixes: af04aa856e93 ("ARM: OMAP: Move dmtimer driver out of plat-omap to drivers under clocksource")
> Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
> ---
>  drivers/clocksource/timer-ti-dm.c | 36 ++++++++++++++++++++++++++++--------
>  1 file changed, 28 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/clocksource/timer-ti-dm.c b/drivers/clocksource/timer-ti-dm.c
> index 09ab29c..5f60f6b 100644
> --- a/drivers/clocksource/timer-ti-dm.c
> +++ b/drivers/clocksource/timer-ti-dm.c
> @@ -140,6 +140,8 @@ struct dmtimer {
>  	struct platform_device *pdev;
>  	struct list_head node;
>  	struct notifier_block nb;
> +	struct notifier_block fclk_nb;
> +	unsigned long fclk_rate;
>  };
>  
>  static u32 omap_reserved_systimers;
> @@ -253,8 +255,7 @@ static inline void __omap_dm_timer_enable_posted(struct dmtimer *timer)
>  	timer->posted = OMAP_TIMER_POSTED;
>  }
>  
> -static inline void __omap_dm_timer_stop(struct dmtimer *timer,
> -					unsigned long rate)
> +static inline void __omap_dm_timer_stop(struct dmtimer *timer)
>  {
>  	u32 l;
>  
> @@ -269,7 +270,7 @@ static inline void __omap_dm_timer_stop(struct dmtimer *timer,
>  		 * Wait for functional clock period x 3.5 to make sure that
>  		 * timer is stopped
>  		 */
> -		udelay(3500000 / rate + 1);
> +		udelay(3500000 / timer->fclk_rate + 1);
>  #endif
>  	}
>  
> @@ -348,6 +349,21 @@ static int omap_timer_context_notifier(struct notifier_block *nb,
>  	return NOTIFY_OK;
>  }
>  
> +static int omap_timer_fclk_notifier(struct notifier_block *nb,
> +				    unsigned long event, void *data)
> +{
> +	struct clk_notifier_data *clk_data = data;
> +	struct dmtimer *timer = container_of(nb, struct dmtimer, fclk_nb);
> +
> +	switch (event) {
> +	case POST_RATE_CHANGE:
> +		timer->fclk_rate = clk_data->new_rate;
> +		return NOTIFY_OK;
> +	default:
> +		return NOTIFY_DONE;
> +	}
> +}
> +
>  static int omap_dm_timer_reset(struct dmtimer *timer)
>  {
>  	u32 l, timeout = 100000;
> @@ -754,7 +770,6 @@ static int omap_dm_timer_stop(struct omap_dm_timer *cookie)
>  {
>  	struct dmtimer *timer;
>  	struct device *dev;
> -	unsigned long rate = 0;
>  
>  	timer = to_dmtimer(cookie);
>  	if (unlikely(!timer))
> @@ -762,10 +777,7 @@ static int omap_dm_timer_stop(struct omap_dm_timer *cookie)
>  
>  	dev = &timer->pdev->dev;
>  
> -	if (!timer->omap1)
> -		rate = clk_get_rate(timer->fclk);
> -
> -	__omap_dm_timer_stop(timer, rate);
> +	__omap_dm_timer_stop(timer);
>  
>  	pm_runtime_put_sync(dev);
>  
> @@ -1124,6 +1136,14 @@ static int omap_dm_timer_probe(struct platform_device *pdev)
>  		timer->fclk = devm_clk_get(dev, "fck");
>  		if (IS_ERR(timer->fclk))
>  			return PTR_ERR(timer->fclk);
> +
> +		timer->fclk_nb.notifier_call = omap_timer_fclk_notifier;
> +		ret = devm_clk_notifier_register(dev, timer->fclk,
> +						 &timer->fclk_nb);
> +		if (ret)
> +			return ret;
> +
> +		timer->fclk_rate = clk_get_rate(timer->fclk);
>  	} else {
>  		timer->fclk = ERR_PTR(-ENODEV);
>  	}
> -- 
> 1.9.1