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

To: yoichi_yuasa@tripeaks.co.jp
Subject: Re: [PATCH][MIPS] add GT641xx timer0 clockevent
From: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Date: Tue, 23 Oct 2007 11:48:24 +0900 (JST)
Cc: ralf@linux-mips.org, linux-mips@linux-mips.org, tglx@linutronix.de
In-reply-to: <200710230214.l9N2EYBa016911@po-mbox301.hop.2iij.net>
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References: <200710230054.l9N0sVv7031267@po-mbox301.hop.2iij.net> <20071023.100645.74754145.nemoto@toshiba-tops.co.jp> <200710230214.l9N2EYBa016911@po-mbox301.hop.2iij.net>
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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?

---
Atsushi Nemoto

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