linux-kernel - Re: CONFIG_PCIEASPM needed for ASPM?

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Message-ID: <20081024024747.GA3900@sli10-desk.sh.intel.com>
Date:	Fri, 24 Oct 2008 10:47:47 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	"Luis R. Rodriguez" <mcgrof@...il.com>
Cc:	"Zhang, Yanmin" <yanmin.zhang@...el.com>,
	Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: Re: CONFIG_PCIEASPM needed for ASPM?

On Fri, Oct 24, 2008 at 09:40:27AM +0800, Luis R. Rodriguez wrote:
> I know, the question is silly right? I thought so too, but I started
> reviewing the code and noticed most of it is just setting up values in
> data structures for the kernel's awareness of capabilities, it also
> updates the state in case of BIOS foobar, and there is also clock
> retraining if possible to reduce latency. Is that it? Did I miss
> something or is it really possible for devices to be able to use
> L0s|L1 or L1 by just having a BIOS which does things correctly?
> 
> That is can our devices be using ASPM without any OS interaction,
> without CONFIG_PCIEASPM enabled?
you didn't miss anything. If BIOS enables ASPM, even OS doesn't do anything,
ASPM will be used. ASPM enter/leave is controlled by hardware, OS just
enables the capability.

Thanks,
Shaohua
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