netdev - Re: [PATCH V10 12/15] ptp: Added a brand new class driver for ptp clocks.

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Message-ID: <20110215172941.GA21150@riccoc20.at.omicron.at>
Date:	Tue, 15 Feb 2011 18:29:41 +0100
From:	Richard Cochran <richardcochran@...il.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	netdev@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Christoph Lameter <cl@...ux.com>,
	David Miller <davem@...emloft.net>,
	Krzysztof Halasa <khc@...waw.pl>,
	Peter Zijlstra <peterz@...radead.org>,
	Rodolfo Giometti <giometti@...ux.it>,
	Thomas Gleixner <tglx@...utronix.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Mike Frysinger <vapier@...too.org>,
	Paul Mackerras <paulus@...ba.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH V10 12/15] ptp: Added a brand new class driver for ptp
 clocks.

On Fri, Feb 11, 2011 at 09:15:24AM +0100, Richard Cochran wrote:
> On Tue, Feb 01, 2011 at 06:00:31PM -0800, John Stultz wrote:
> > So what is serializing access to the timestamp_event_queue here? I don't
> > see any usage of tsevq_mux by the callers. Am I missing it? It looks
> > like its called from interrupt context, so do you really need a spinlock
> > and not a mutex here?
> 
> The external timestamp FIFO is written only from interrupt context.

Oops, I lied. After reworking the phyter driver, I find that I want to
enqueue time stamps from non-interrupt contexts, too.

So, you are right. This will need a spin lock...

Thanks,

Richard
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