linux-kernel - Re: [PATCH] ata: ahci: power off unused ports

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Message-ID: <48444160.50308@garzik.org>
Date:	Mon, 02 Jun 2008 14:52:16 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	rwheeler@...hat.com
CC:	kristen.c.accardi@...el.com, Mark Lord <liml@....ca>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Pavel Machek <pavel@....cz>, Theodore Tso <tytso@....edu>,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ata: ahci: power off unused ports

Ric Wheeler wrote:
> Jeff Garzik wrote:
>> Ric Wheeler wrote:
>>> Kristen Carlson Accardi wrote:
>>>> Not all drivers will need a user interface to turn off hotplug
>>>> I would think.  At any rate - I would think it'd be better to let
>>>> driver writers decide how they want their drivers to behave wrt
>>>> hotplug and power instead of forcing a generic policy on everyone.
>>>>
>>>> This patch would provide users of AHCI controllers a way to save
>>>> power now, while you work on the grand scheme for polling/turning on 
>>>> off
>>>> hotplug via sysfs.  It's an interim solution that impacts nobody but
>>>> ahci users and is can be easily integrated into whatever solution you
>>>> eventually work out.
>>
>>> I like the patch -  it seems that it will help a lot of users out 
>>> near term in a very positive way while we iterate on the broader 
>>> solution,
>>
>> A better patch would enable the _possibility_ of power savings on 
>> non-AHCI chips, and not add a one-off AHCI-specific user interface 
>> that must be supported for years to come.
>>
>>     Jeff
> I think that the patch does that first part pretty reasonably for all 
> chips as Kristen explained before.
> 
> If the user interface is the only obstacle and the base code seems to be 
> flexible enough for any device to take advantage of, it would still seem 
> to be a positive step forward to put in that base functionality (even 
> without the module param) to enable power saving.
> 
> It is always good to get the complete solution in (how hard can the user 
> interface be to code once we agree on what it should be ;-)), but this 
> seems to be a good first step.

A prep step without the module param (ie. user interface) is fine. 
That's how we deployed Async Notification.  Kristen's AN stuff went into 
libata well before the SCSI API was settled upon.

	Jeff




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