linux-kernel - Re: [RFC] Reentrant clock sources

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Message-Id: <1227669624.6298.11.camel@localhost>
Date:	Tue, 25 Nov 2008 19:20:24 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Magnus Damm <magnus.damm@...il.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	lethal@...ux-sh.org, mingo@...hat.com
Subject: Re: [RFC] Reentrant clock sources

On Wed, 2008-11-26 at 04:07 +0100, Ingo Molnar wrote:
> * Thomas Gleixner <tglx@...utronix.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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