linux-kernel - Re: [PATCH] arm: at91: do not disable/enable clocks in a row

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Date:	Tue, 29 Mar 2016 15:32:40 +0200
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm: at91: do not disable/enable clocks in a row

Le 29/03/2016 15:26, Sebastian Andrzej Siewior a écrit :
> Currently the driver will disable the clock and enable it one line later
> if it is switching from periodic mode into one shot.
> This can be avoided and causes a needless warning on -RT.
> 
> Tested-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> Acked-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Absolutely makes sense:
Acked-by: Nicolas Ferre <nicolas.ferre@...el.com>

Thanks.

> ---
>  drivers/clocksource/tcb_clksrc.c | 33 +++++++++++++++++++++++++++++----
>  1 file changed, 29 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/clocksource/tcb_clksrc.c b/drivers/clocksource/tcb_clksrc.c
> index 4da2af9694a2..ed1ae4445e8d 100644
> --- a/drivers/clocksource/tcb_clksrc.c
> +++ b/drivers/clocksource/tcb_clksrc.c
> @@ -74,6 +74,7 @@ static struct clocksource clksrc = {
>  struct tc_clkevt_device {
>  	struct clock_event_device	clkevt;
>  	struct clk			*clk;
> +	bool				clk_enabled;
>  	void __iomem			*regs;
>  };
>  
> @@ -91,6 +92,24 @@ static struct tc_clkevt_device *to_tc_clkevt(struct clock_event_device *clkevt)
>   */
>  static u32 timer_clock;
>  
> +static void tc_clk_disable(struct clock_event_device *d)
> +{
> +	struct tc_clkevt_device *tcd = to_tc_clkevt(d);
> +
> +	clk_disable(tcd->clk);
> +	tcd->clk_enabled = false;
> +}
> +
> +static void tc_clk_enable(struct clock_event_device *d)
> +{
> +	struct tc_clkevt_device *tcd = to_tc_clkevt(d);
> +
> +	if (tcd->clk_enabled)
> +		return;
> +	clk_enable(tcd->clk);
> +	tcd->clk_enabled = true;
> +}
> +
>  static int tc_shutdown(struct clock_event_device *d)
>  {
>  	struct tc_clkevt_device *tcd = to_tc_clkevt(d);
> @@ -98,8 +117,14 @@ static int tc_shutdown(struct clock_event_device *d)
>  
>  	__raw_writel(0xff, regs + ATMEL_TC_REG(2, IDR));
>  	__raw_writel(ATMEL_TC_CLKDIS, regs + ATMEL_TC_REG(2, CCR));
> +	return 0;
> +}
> +
> +static int tc_shutdown_clk_off(struct clock_event_device *d)
> +{
> +	tc_shutdown(d);
>  	if (!clockevent_state_detached(d))
> -		clk_disable(tcd->clk);
> +		tc_clk_disable(d);
>  
>  	return 0;
>  }
> @@ -112,7 +137,7 @@ static int tc_set_oneshot(struct clock_event_device *d)
>  	if (clockevent_state_oneshot(d) || clockevent_state_periodic(d))
>  		tc_shutdown(d);
>  
> -	clk_enable(tcd->clk);
> +	tc_clk_enable(d);
>  
>  	/* slow clock, count up to RC, then irq and stop */
>  	__raw_writel(timer_clock | ATMEL_TC_CPCSTOP | ATMEL_TC_WAVE |
> @@ -134,7 +159,7 @@ static int tc_set_periodic(struct clock_event_device *d)
>  	/* By not making the gentime core emulate periodic mode on top
>  	 * of oneshot, we get lower overhead and improved accuracy.
>  	 */
> -	clk_enable(tcd->clk);
> +	tc_clk_enable(d);
>  
>  	/* slow clock, count up to RC, then irq and restart */
>  	__raw_writel(timer_clock | ATMEL_TC_WAVE | ATMEL_TC_WAVESEL_UP_AUTO,
> @@ -168,7 +193,7 @@ static struct tc_clkevt_device clkevt = {
>  		/* Should be lower than at91rm9200's system timer */
>  		.rating			= 125,
>  		.set_next_event		= tc_next_event,
> -		.set_state_shutdown	= tc_shutdown,
> +		.set_state_shutdown	= tc_shutdown_clk_off,
>  		.set_state_periodic	= tc_set_periodic,
>  		.set_state_oneshot	= tc_set_oneshot,
>  	},
> 


-- 
Nicolas Ferre