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

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Date:	Fri, 24 Apr 2009 12:01:00 +0200
From:	Alessandro Zummo <alessandro.zummo@...ertech.it>
To:	rtc-linux@...glegroups.com
Cc:	david-b@...bell.net, Atsushi Nemoto <anemo@....ocn.ne.jp>,
	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 02:31:12 -0700
David Brownell <david-b@...bell.net> wrote:

 
> >  and 
> >  acquired with the standard spinlock calls in the irq
> >  handler.
> 
> Which "standard" call?  "spin_lock", "spin_lock_irqsave",
> and "spin_lock_irq" are all standard calls.

 sorry, I mean the no irq version of the call.


> Recall that it's not the IRQ handler that's directly
> grabbing the lock; it's code called by that handler.

 
> >  would it work?
> 
> The patch I saw -- switching rtc_update_irq() to use
> spin_lock_irqsave() -- would work, but it's incomplete.
> It left the doc broken, and didn't clean up the drivers
> which did the real work to obey the current call spec.

 that patch is a no go. period. I'm not talking about it.


> It'd be much nicer if lockdep would just do the right
> thing and report when IRQ handlers do stupid things,
> instead of covering up that class of bugs.  But I'm told
> it will not get fixed; sigh.

 I'm not tying to fix call issues or lockdep politics,
 just to understand if it's possible to avoid disabling the IRQs.

 i.e.,

 use spin_lock() in the IRQ handler and spin_lock_irq/irq_save
 in the setup functions.

 


-- 

 Best regards,

 Alessandro Zummo,
  Tower Technologies - Torino, Italy

  http://www.towertech.it

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