linux-kernel - Re: [PATCH] tick: add check for the existence of broadcast clock event device

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Message-ID: <alpine.LFD.2.00.0906080739020.3419@localhost.localdomain>
Date:	Mon, 8 Jun 2009 07:43:43 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Feng Tang <feng.tang@...el.com>
cc:	"mingo@...e.hu" <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	shaohua.li@...el.com, jacob.jun.pan@...el.com
Subject: Re: [PATCH] tick: add check for the existence of broadcast clock
 event device

On Mon, 8 Jun 2009, Feng Tang wrote:
> > 1) How do you calibrate the local APIC timer if you do not have some
> > initial timer device ?
> Yes, we have external timer device with the name "apbt"

So that timer is initialized and registered before the local apic,
right ?

Why is the local APIC timer used at all ? The apbt timer should have a
higher rating as the local APIC timer, so when APIC is registered it
is not selected and the check in the broadcast functions

   !(dev->features & CLOCK_EVT_FEAT_C3STOP))

should protect you because that bit is not set on your apbt device.

Thanks,

	tglx
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