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From: David Brownell <david-b@pacbell.net>
To: Ingo Molnar <mingo@elte.hu>
Subject: Re: [patch 2.6.24-rc2 1/3] generic gpio -- gpio_chip support
Date: Tue, 13 Nov 2007 11:22:45 -0800
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Cc: Andrew Morton <akpm@linux-foundation.org>,
       Linux Kernel list <linux-kernel@vger.kernel.org>,
       Florian Fainelli <florian.fainelli@telecomint.eu>,
       Haavard Skinnemoen <hskinnemoen@atmel.com>,
       Nick Piggin <nickpiggin@yahoo.com.au>
References: <200711091136.20051.david-b@pacbell.net> <200711121726.39263.david-b@pacbell.net> <20071113093414.GA5270@elte.hu>
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On Tuesday 13 November 2007, Ingo Molnar wrote:
> 
> * David Brownell <david-b@pacbell.net> wrote:
> 
> > > > I speculate that either the design has changed (without fanfare), 
> > > > or else that stuff is in RT kernels and has not yet gone upstream.
> > > 
> > > Well whatever.  We shouldn't have to resort to caller-side party 
> > > tricks like this to get acceptable performance.
> > 
> > I'd be happy if, as originally presented, it were possible to just 
> > pass a raw_spinlock_t to spin_lock_irqsave() and friends.
> 
> that's a spinlock type abstraction of PREEMPT_RT, not of mainline.

Any reason that stuff shouldn't move into mainline?


> 	 Why do you want to use raw_spinlock_t?

Already answered elsewhere in this thread ... I'll highlight the
point that such bitops shouldn't be preemption points.