linux-kernel - Re: [PATCH 2/2] rtc: asm9260: rework locking

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Date:   Wed, 31 Aug 2016 18:09:40 +0200
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Oleksij Rempel <linux@...pel-privat.de>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        rtc-linux@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] rtc: asm9260: rework locking

On 31/08/2016 at 17:14:27 +0200, Oleksij Rempel wrote :
> Hi
> 
> Am 31.08.2016 um 02:18 schrieb Alexandre Belloni:
> > The rtc-asm9260 driver uses a discrete spinlock (wrongly uninitialized).
> > Use the rtc mutex to lock mmio accesses instead.
> > 
> > Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> > ---
> >  drivers/rtc/rtc-asm9260.c | 16 ++--------------
> >  1 file changed, 2 insertions(+), 14 deletions(-)
> > 
> > diff --git a/drivers/rtc/rtc-asm9260.c b/drivers/rtc/rtc-asm9260.c
> > index 5219916ce11d..812f131da694 100644
> > --- a/drivers/rtc/rtc-asm9260.c
> > +++ b/drivers/rtc/rtc-asm9260.c
> > @@ -112,8 +112,6 @@ struct asm9260_rtc_priv {
> >  	void __iomem		*iobase;
> >  	struct rtc_device	*rtc;
> >  	struct clk		*clk;
> > -	/* io lock */
> > -	spinlock_t		lock;
> >  };
> >  
> >  static irqreturn_t asm9260_rtc_irq(int irq, void *dev_id)
> > @@ -122,11 +120,13 @@ static irqreturn_t asm9260_rtc_irq(int irq, void *dev_id)
> >  	u32 isr;
> >  	unsigned long events = 0;
> >  
> > +	mutex_lock(&priv->rtc->ops_lock);
> >  	isr = ioread32(priv->iobase + HW_CIIR);
> >  	if (!isr)
> >  		return IRQ_NONE;
> >  
> >  	iowrite32(0, priv->iobase + HW_CIIR);
> > +	mutex_unlock(&priv->rtc->ops_lock);
> 
> This means if we have shared or spurious interrupt we will get a
> deadlock here?
> 

True, I'll fix that. I actually got it right at first and then I toyed
with sparse/smatch to see whether it was properly checking the locking.
Seems like my setup was not correct. Thanks for the review !

> 
> >  	events |= RTC_AF | RTC_IRQF;
> >  
> > @@ -139,9 +139,7 @@ static int asm9260_rtc_read_time(struct device *dev, struct rtc_time *tm)
> >  {
> >  	struct asm9260_rtc_priv *priv = dev_get_drvdata(dev);
> >  	u32 ctime0, ctime1, ctime2;
> > -	unsigned long irq_flags;
> >  
> > -	spin_lock_irqsave(&priv->lock, irq_flags);
> >  	ctime0 = ioread32(priv->iobase + HW_CTIME0);
> >  	ctime1 = ioread32(priv->iobase + HW_CTIME1);
> >  	ctime2 = ioread32(priv->iobase + HW_CTIME2);
> > @@ -155,7 +153,6 @@ static int asm9260_rtc_read_time(struct device *dev, struct rtc_time *tm)
> >  		ctime1 = ioread32(priv->iobase + HW_CTIME1);
> >  		ctime2 = ioread32(priv->iobase + HW_CTIME2);
> >  	}
> > -	spin_unlock_irqrestore(&priv->lock, irq_flags);
> >  
> >  	tm->tm_sec  = (ctime0 >> BM_CTIME0_SEC_S)  & BM_CTIME0_SEC_M;
> >  	tm->tm_min  = (ctime0 >> BM_CTIME0_MIN_S)  & BM_CTIME0_MIN_M;
> > @@ -174,9 +171,7 @@ static int asm9260_rtc_read_time(struct device *dev, struct rtc_time *tm)
> >  static int asm9260_rtc_set_time(struct device *dev, struct rtc_time *tm)
> >  {
> >  	struct asm9260_rtc_priv *priv = dev_get_drvdata(dev);
> > -	unsigned long irq_flags;
> >  
> > -	spin_lock_irqsave(&priv->lock, irq_flags);
> >  	/*
> >  	 * make sure SEC counter will not flip other counter on write time,
> >  	 * real value will be written at the enf of sequence.
> > @@ -191,7 +186,6 @@ static int asm9260_rtc_set_time(struct device *dev, struct rtc_time *tm)
> >  	iowrite32(tm->tm_hour, priv->iobase + HW_HOUR);
> >  	iowrite32(tm->tm_min,  priv->iobase + HW_MIN);
> >  	iowrite32(tm->tm_sec,  priv->iobase + HW_SEC);
> > -	spin_unlock_irqrestore(&priv->lock, irq_flags);
> >  
> >  	return 0;
> >  }
> > @@ -199,9 +193,7 @@ static int asm9260_rtc_set_time(struct device *dev, struct rtc_time *tm)
> >  static int asm9260_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
> >  {
> >  	struct asm9260_rtc_priv *priv = dev_get_drvdata(dev);
> > -	unsigned long irq_flags;
> >  
> > -	spin_lock_irqsave(&priv->lock, irq_flags);
> >  	alrm->time.tm_year = ioread32(priv->iobase + HW_ALYEAR);
> >  	alrm->time.tm_mon  = ioread32(priv->iobase + HW_ALMON);
> >  	alrm->time.tm_mday = ioread32(priv->iobase + HW_ALDOM);
> > @@ -213,7 +205,6 @@ static int asm9260_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
> >  
> >  	alrm->enabled = ioread32(priv->iobase + HW_AMR) ? 1 : 0;
> >  	alrm->pending = ioread32(priv->iobase + HW_CIIR) ? 1 : 0;
> > -	spin_unlock_irqrestore(&priv->lock, irq_flags);
> >  
> >  	return rtc_valid_tm(&alrm->time);
> >  }
> > @@ -221,9 +212,7 @@ static int asm9260_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
> >  static int asm9260_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
> >  {
> >  	struct asm9260_rtc_priv *priv = dev_get_drvdata(dev);
> > -	unsigned long irq_flags;
> >  
> > -	spin_lock_irqsave(&priv->lock, irq_flags);
> >  	iowrite32(alrm->time.tm_year, priv->iobase + HW_ALYEAR);
> >  	iowrite32(alrm->time.tm_mon,  priv->iobase + HW_ALMON);
> >  	iowrite32(alrm->time.tm_mday, priv->iobase + HW_ALDOM);
> > @@ -234,7 +223,6 @@ static int asm9260_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
> >  	iowrite32(alrm->time.tm_sec,  priv->iobase + HW_ALSEC);
> >  
> >  	iowrite32(alrm->enabled ? 0 : BM_AMR_OFF, priv->iobase + HW_AMR);
> > -	spin_unlock_irqrestore(&priv->lock, irq_flags);
> >  
> >  	return 0;
> >  }
> > 
> 
> 
> -- 
> Regards,
> Oleksij
> 




-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com