From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <htejun@gmail.com>
Subject: Re: [ANNOUNCE] libata EH/NCQ/hotplug/PM git tree
Date: Sat, 13 May 2006 13:19:50 +0900
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To: Jeff Garzik <jgarzik@pobox.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, Albert Lee <albertcc@tw.ibm.com>, Jens Axboe <axboe@suse.de>, Edward Falk <efalk@google.com>, Carlos Pardo <Carlos.Pardo@siliconimage.com>, Raymond Liu <Raymond.Liu@siliconimage.com>, "linux-ide@vger.kernel.org" <linux-ide@vger.kernel.org>

Jeff Garzik wrote:
> Tejun Heo wrote:
>> That cmd-switching PM support is what AHCI SPM bit indicates.  As of 
>> v1.1, AHCI doesn't define FIS-switching PM support yet.
> 
> Right you are; see, told you my brain was frazzled.
> 
> 
>> Which is understandable considering AHCI doesn't construct FISes 
>> itself.  I don't think PM requires more hardware support than being 
>> capable for setting PMP in the FISes, which AHCI certainly can 
>> (standing down on collision for SDB notify aside).  I can give it a 
>> shot but it clearly violates the spec, and even if it works, we would 
>> need to print big fat warning message while attaching PM.
> 
> Setting the PMP field during FIS construction would work, I should 
> think, for outgoing FIS's.  Not sure how incoming FISs would behave.
> 

I think the incoming part will work too.  All it has to do is ignoring 
it.  SDB notify can also implemented using Unknown FIS interrupt and FIS 
reception area.  I'll give it a shot.  After all, working with big fat 
warning is a lot better than not working, and a LOT of AHCIs are out there.

-- 
tejun