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

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Date:	Tue, 9 Jun 2009 05:49:58 -0700
From:	"Pan, Jacob jun" <jacob.jun.pan@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"Tang, Feng" <feng.tang@...el.com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Li, Shaohua" <shaohua.li@...el.com>
Subject: RE: [PATCH] tick: add check for the existence of broadcast clock
 event device

Thanks for the explanations, I will add the secondary clock code to the
 x86_quirks. It should be submitted for review soon.

Jacob

>-----Original Message-----
>From: Thomas Gleixner [mailto:tglx@...utronix.de]
>Sent: Tuesday, June 09, 2009 1:19 AM
>To: Pan, Jacob jun
>Cc: Tang, Feng; mingo@...e.hu; linux-kernel@...r.kernel.org; Li, Shaohua
>Subject: RE: [PATCH] tick: add check for the existence of broadcast clock event
>device
>
>On Mon, 8 Jun 2009, Pan, Jacob jun wrote:
>> >I understand that, but HPET does not rely on some magic events
>> >happening. That's what I'm worried about. The boot code is fragile and
>> >I prefer some explicit setup call over a fragile solution which
>> >happens to work.
>> >
>> >There is not much to complain about a platform specific function call
>> >to set up special devices if there is a requirement for a call order.
>> >
>> >In fact you can avoid setting up the local APIC timer at all. So what
>> >you want is something like the patch below. You can set the
>> >setup_secondary_clock pointer in the quirks structure when you detect
>> >that you are running on such a system.
>> >
>
>> [[JPAN]] Hi Thomas, I have been developing the APB timer driver as
>> Feng mentioned, thank you for the suggestions.  I agree with you
>> that direct setting up secondary clockevent is a better solution.
>> But maybe I misunderstand the HPET code, isn't it true that per CPU
>> HPET timer also rely on IPI? In hpet_cpuhp_notify().
>
>Well the difference is, that the HPET setup always has a functional
>clock event device (local APIC + the broadcast fallback) and it does
>not depend on that IPI to make progress.
>
>> Also for using x86_quirks, I think the default quirks are more
>> generic in the sense of x86 platform, but here we are really
>> choosing timer device, so can we switch based on availability of the
>> timer devices instead of quirks? Otherwise, if more platforms share
>> the same setup_secondary_clock() quirk, we would have to check for
>> timer devices anyway.
>
>The quirks mechanism is exactly the right thing. It provides platforms
>and I consider your system a platform which has neither PIT nor HPET a
>mechanism to override the default implementation. And overriding the
>default local APIC timer setup is exaclty what you want to do.
>
>Thanks,
>
>	tglx
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