linux-kernel - Re: [RFC PATCH 3/3] rtc: at91sam9: properly act when IRQ handler is called in suspended state

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Message-ID: <1611142.77NqGpG2im@vostro.rjw.lan>
Date:	Wed, 25 Feb 2015 23:05:36 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Mark Rutland <mark.rutland@....com>,
	linux-kernel@...r.kernel.org,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 3/3] rtc: at91sam9: properly act when IRQ handler is called in suspended state

On Tuesday, February 24, 2015 10:56:02 AM Boris Brezillon wrote:
> The IRQ line used by the RTC device is often shared with the system timer
> (PIT) on at91 platforms.
> Since timers are registering their handlers with IRQF_NO_SUSPEND, we should
> expect being called in suspended state, and properly wake the system up
> when this is the case.
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> ---
>  drivers/rtc/rtc-at91sam9.c | 62 ++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 51 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-at91sam9.c b/drivers/rtc/rtc-at91sam9.c
> index 2183fd2..8cf9c1b 100644
> --- a/drivers/rtc/rtc-at91sam9.c
> +++ b/drivers/rtc/rtc-at91sam9.c
> @@ -77,6 +77,8 @@ struct sam9_rtc {
>  	unsigned int		gpbr_offset;
>  	int 			irq;
>  	struct clk		*sclk;
> +	unsigned long		events;
> +	spinlock_t		lock;
>  };
>  
>  #define rtt_readl(rtc, field) \
> @@ -271,14 +273,9 @@ static int at91_rtc_proc(struct device *dev, struct seq_file *seq)
>  	return 0;
>  }
>  
> -/*
> - * IRQ handler for the RTC
> - */
> -static irqreturn_t at91_rtc_interrupt(int irq, void *_rtc)
> +static irqreturn_t at91_rtc_cache_events(struct sam9_rtc *rtc)
>  {
> -	struct sam9_rtc *rtc = _rtc;
>  	u32 sr, mr;
> -	unsigned long events = 0;
>  
>  	/* Shared interrupt may be for another device.  Note: reading
>  	 * SR clears it, so we must only read it in this irq handler!
> @@ -290,18 +287,54 @@ static irqreturn_t at91_rtc_interrupt(int irq, void *_rtc)
>  
>  	/* alarm status */
>  	if (sr & AT91_RTT_ALMS)
> -		events |= (RTC_AF | RTC_IRQF);
> +		rtc->events |= (RTC_AF | RTC_IRQF);
>  
>  	/* timer update/increment */
>  	if (sr & AT91_RTT_RTTINC)
> -		events |= (RTC_UF | RTC_IRQF);
> +		rtc->events |= (RTC_UF | RTC_IRQF);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static void at91_rtc_flush_events(struct sam9_rtc *rtc)
> +{
> +	if (!rtc->events)
> +		return;
>  
> -	rtc_update_irq(rtc->rtcdev, 1, events);
> +	rtc_update_irq(rtc->rtcdev, 1, rtc->events);
> +	rtc->events = 0;
>  
>  	pr_debug("%s: num=%ld, events=0x%02lx\n", __func__,
> -		events >> 8, events & 0x000000FF);
> +		rtc->events >> 8, rtc->events & 0x000000FF);
> +}
>  
> -	return IRQ_HANDLED;
> +/*
> + * IRQ handler for the RTC
> + */
> +static irqreturn_t at91_rtc_interrupt(int irq, void *_rtc)
> +{
> +	struct sam9_rtc *rtc = _rtc;
> +	int ret;
> +
> +	spin_lock(&rtc->lock);
> +
> +	ret = at91_rtc_cache_events(rtc);
> +
> +	/* We're called in suspended state */
> +	if (irq_is_wakeup_armed(irq)) {

Instead of doing this, I would set a flag in the driver's ->suspend
callback (or in ->suspend_late, whichever is more convenient) and check
that flag here.

> +		/* Mask irqs coming from this peripheral */
> +		rtt_writel(rtc, MR,
> +			   rtt_readl(rtc, MR) &
> +			   ~(AT91_RTT_ALMIEN | AT91_RTT_RTTINCIEN));
> +		/* Trigger a system wakeup */
> +		irq_pm_force_wakeup();
> +	} else {
> +		at91_rtc_flush_events(rtc);
> +	}
> +
> +	spin_unlock(&rtc->lock);
> +
> +	return ret;
>  }
>  
>  static const struct rtc_class_ops at91_rtc_ops = {
> @@ -499,10 +532,17 @@ static int at91_rtc_resume(struct device *dev)
>  	u32		mr;
>  
>  	if (rtc->imr) {
> +		unsigned long flags;
> +
>  		if (device_may_wakeup(dev))
>  			disable_irq_wake(rtc->irq);
>  		mr = rtt_readl(rtc, MR);
>  		rtt_writel(rtc, MR, mr | rtc->imr);
> +
> +		spin_lock_irqsave(&rtc->lock, flags);
> +		at91_rtc_cache_events(rtc);
> +		at91_rtc_flush_events(rtc);
> +		spin_unlock_irqrestore(&rtc->lock, flags);
>  	}
>  
>  	return 0;
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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