linux-kernel - Re: [PATCH 1/2] tick: broadcast: Deny per-cpu clockevents from being broadcast sources

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Date:	Thu, 22 Aug 2013 16:38:48 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Stephen Boyd <sboyd@...eaurora.org>
CC:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Michal Simek <michal.simek@...inx.com>,
	Russell King <linux@....linux.org.uk>,
	<linux-kernel@...r.kernel.org>,
	Stuart Menefy <stuart.menefy@...com>,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	<linux-arm-kernel@...ts.infradead.org>,
	<srinivas.kandagatla@...com>
Subject: Re: [PATCH 1/2] tick: broadcast: Deny per-cpu clockevents from being
 broadcast sources

On Thu, Aug 22, 2013 at 10:06:40AM -0700, Stephen Boyd wrote:
> On most ARM systems the per-cpu clockevents are truly per-cpu in
> the sense that they can't be controlled on any other CPU besides
> the CPU that they interrupt. If one of these clockevents were to
> become a broadcast source we will run into a lot of trouble
> because the broadcast source is enabled on the first CPU to go
> into deep idle (if that CPU suffers from FEAT_C3_STOP) and that
> could be a different CPU than what the clockevent is interrupting
> (or even worse the CPU that the clockevent interrupts could be
> offline).
> 
> Theoretically it's possible to support per-cpu clockevents as the
> broadcast source but so far we haven't needed this and supporting
> it is rather complicated. Let's just deny the possibility for now
> until this becomes a reality (let's hope it never does!).
> 
> Reported-by: Sören Brinkmann <soren.brinkmann@...inx.com>
> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
Tested-by: Sören Brinkmann <soren.brinkmann@...inx.com>

This fixes the issue I reported when enabling the global timer on Zynq.
The global timer is prevented from becoming the broadcast device and my
system boots.

	Thanks,
	Sören


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