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Re: [PATCH][MIPS] add GT641xx timer0 clockevent

To: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Subject: Re: [PATCH][MIPS] add GT641xx timer0 clockevent
From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 23 Oct 2007 07:21:28 +0200 (CEST)
Cc: yoichi_yuasa@tripeaks.co.jp, ralf@linux-mips.org, linux-mips@linux-mips.org
In-reply-to: <20071023.114824.122622188.nemoto@toshiba-tops.co.jp>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <200710230054.l9N0sVv7031267@po-mbox301.hop.2iij.net> <20071023.100645.74754145.nemoto@toshiba-tops.co.jp> <200710230214.l9N2EYBa016911@po-mbox301.hop.2iij.net> <20071023.114824.122622188.nemoto@toshiba-tops.co.jp>
Sender: linux-mips-bounce@linux-mips.org
On Tue, 23 Oct 2007, Atsushi Nemoto wrote:
> Added Thomas Gleixner for CC list.
> 
> On Tue, 23 Oct 2007 11:15:58 +0900, Yoichi Yuasa 
> <yoichi_yuasa@tripeaks.co.jp> wrote:
> > > > > These clockevent routines are always called with interrupt disabled,
> > > > > so I suppose those spin_lock_irqsave/spin_unlock_irqrestore pairs can
> > > > > be omitted. (or this timer can be used on SMP?)
> > > > 
> > > > Yes, it can be used on Malta(SMP).
> > > 
> > > Then spin_lock()/spin_unlock() is enough, isn't it?
> > 
> > The timer control register(GT_TC_CONTROL_OFS) is shared with 4 timers.
> > The 4 timers are connected with separate IRQ. 
> > 
> > clockevents_program_event() and clockevents_set_mode() can be called from
> > anywhere(in the kernel).
> > 
> > I think that it's necessary for it.
> 
> Hmm... clockevents_set_mode() must be called with interrupt disabled
> as stated in its comment.  There are no such a comment for
> clockevents_program_event(), but it is always called with interrupt
> disabled if the interrupt for the event was registered with
> IRQF_DISABLED flag.
> 
> I agree that saving/restoring irq_flag would be safer, but I think it
> can be omitted at least for now.
> 
> If clockevents_program_event() could be called with interrupt enabled,
> mips_next_event() in cevt-r4k.c should be fixed.
> 
> 
> Thomas, clockevents_program_event() (or ->set_next_event() method for
> clock_event_device) is supposed to be called with interrupt enabled?

Actually all call sites have interrupts disabled right now and I can
not think of a reason why we would ever call with interrupts
enabled. Time to add some comment.

         tglx

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