linux-kernel - Re: [rtc-linux] Re: [PATCH] rtc: Make rtc_update

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Message-Id: <20090425.214015.108306850.anemo@mba.ocn.ne.jp>
Date:	Sat, 25 Apr 2009 21:40:15 +0900 (JST)
From:	Atsushi Nemoto <anemo@....ocn.ne.jp>
To:	alessandro.zummo@...ertech.it
Cc:	rtc-linux@...glegroups.com, david-b@...bell.net,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	hcegtvedt@...el.com, vapier@...too.org, rongkai.zhan@...driver.com,
	balajirrao@...nmoko.org, broonie@...nsource.wolfsonmicro.com
Subject: Re: [rtc-linux] Re: [PATCH] rtc: Make rtc_update_irq callable with
 irqs enabled

On Fri, 24 Apr 2009 21:41:17 +0200, Alessandro Zummo <alessandro.zummo@...ertech.it> wrote:
> >  RTC alarm interrupt handler takes rtc->irq_lock by spin_lock()
> > > 2. A timer interrupt handler calls rtc_uie_timer() for UIE emulation
> > > 3. rtc_uie_timer() waits on rtc->irq_lock .... deadlock!  
> > 
> > Oops, this is wrong.  This deadlock cannot happen since
> > rtc_uie_timer() will be called in bh (softirq) context, not interrupt
> > context.
> 
>  Correct.
> 
>  And we have only one irq handler per driver. Anything else?

Some drivers (omap, pxa, etc.) have multiple irq handler.  Currently
all such drivers use IRQF_DISABLED so I do not see any real problem
now.

So I think my patch is rather "cleanup and bulletproof" than "bugfix".

---
Atsushi Nemoto
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