Subject: Re: [RFC] Reentrant clock sources
From: john stultz <johnstul@us.ibm.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>, Magnus Damm <magnus.damm@gmail.com>,
       linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
       lethal@linux-sh.org, mingo@redhat.com
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	 <alpine.LFD.2.00.0811252215270.3235@localhost.localdomain>
	 <20081126030720.GC8242@elte.hu>
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Date: Tue, 25 Nov 2008 19:20:24 -0800
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On Wed, 2008-11-26 at 04:07 +0100, Ingo Molnar wrote:
> * Thomas Gleixner <tglx@linutronix.de> wrote:
> 
> > > +	cycle_t (*vread)(struct clocksource *cs);
> > 
> > This is crap. vread can not access the clocksource.
> 
> i think 'reentrant' in the sense of creating self-sufficient driver 
> entities. vread wont (and shouldnt) call ->vread() recursively - but 
> it might want to access fields on the clocksource.

I think Thomas' issue is that vread() *cannot* access fields on the
clocksource (since vread has to be careful not to access any
non-vsyscall mapped memory).

However not all clocksources use vread(), but really I'm not quite clear
on what one would want to access in the clocksource structure when
making a ->read() call.

So maybe a further description of what specific need motivates this
change would be helpful? The brief description of power management
doesn't quite click in my head yet.

thanks
-john

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