linux-kernel - Re: [PATCH v2 3/4] tick: broadcast: Deny per-cpu clockevents from being broadcast sources

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Message-ID: <5242FD32.7030008@linaro.org>
Date:	Wed, 25 Sep 2013 17:11:46 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Soren Brinkmann <soren.brinkmann@...inx.com>,
	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Russell King <linux@....linux.org.uk>,
	Michal Simek <michal.simek@...inx.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Preeti Murthy <preeti.lkml@...il.com>
CC:	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 3/4] tick: broadcast: Deny per-cpu clockevents from
 being broadcast sources

On 09/18/2013 08:48 PM, Soren Brinkmann 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!).
> 
> Signed-off-by: Soren Brinkmann <soren.brinkmann@...inx.com>

Acked-by: Daniel Lezcano <daniel.lezcano@...aro.org>

> ---
>  kernel/time/tick-broadcast.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
> index 218bcb5..9532690 100644
> --- a/kernel/time/tick-broadcast.c
> +++ b/kernel/time/tick-broadcast.c
> @@ -70,6 +70,7 @@ static bool tick_check_broadcast_device(struct clock_event_device *curdev,
>  					struct clock_event_device *newdev)
>  {
>  	if ((newdev->features & CLOCK_EVT_FEAT_DUMMY) ||
> +	    (newdev->features & CLOCK_EVT_FEAT_PERCPU) ||
>  	    (newdev->features & CLOCK_EVT_FEAT_C3STOP))
>  		return false;
>  
> 


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