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

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Date:	Mon, 02 Jun 2008 09:03:04 -0400
From:	Mark Lord <liml@....ca>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, Pavel Machek <pavel@....cz>,
	Kristen Carlson Accardi <kristen.c.accardi@...el.com>,
	Theodore Tso <tytso@....edu>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ata: ahci: power off unused ports

Jeff Garzik wrote:
> Alan Cox wrote:
>>> If you are talking about SATA -- incorrect.
>>>
>>> The patch deals with policy, and the user MUST have the ability to 
>>> control this stuff.  Otherwise you create a situation where the user 
>>> might be denied hotplug use in valid cases, or similar negative 
>>> situations.
>>
>> The policy isn't however complicated. Tejun added the stuff for forcing
>> cable type and mode on setup and has therefore written all the per device
>> setup code we might need. Alternatively a single
>>
>>     foo=1/0
>>
>> option has been fine for acpi and will do fine for this. Total additional
>> cost - 1 line.
> 
> The key requirement is per-port control.  Ideally via hdparm or another 
> userspace tool, but kernel command line (module options) or sysfs would 
> be just fine too.  And agreed, the minimal you need is simply 1/0 for 
> the port's policy.
..

Btw.. hdparm-8.7 (unreleased) can grok /sys now, so that interface is
as good as any from a userspace viewpoint now.

For the power-off of unused ports, the current patch still sounds
extremely vendor-specific (Intel).

Does it actually work (demonstrate, please) on any other hardware ?

I would still like to see a far more generic solution, with periodic polling
and the like, which would permit use on *any* machines (eg. data centers)
without loss of hotplug capability on those ports.

But that's probably just wishful thinking at this point.

Cheers
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