linux-kernel - Re: [RFC][PATCH 4/4] ahci: support hot plug when port/controller is runtime suspended

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Message-ID: <CAPXgP12mEC_p_7Xi-pzKwUCNV1=WTj7rW+upXK6gUbGwg3S2NA@mail.gmail.com>
Date:	Fri, 16 Dec 2011 00:29:44 +0100
From:	Kay Sievers <kay.sievers@...y.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Lin Ming <ming.m.lin@...el.com>, Jeff Garzik <jgarzik@...ox.com>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	David Zeuthen <zeuthen@...il.com>
Subject: Re: [RFC][PATCH 4/4] ahci: support hot plug when port/controller is
 runtime suspended

On Thu, Dec 15, 2011 at 20:21, Tejun Heo <tj@...nel.org> wrote:
> On Thu, Dec 15, 2011 at 09:12:49PM +0800, Lin Ming wrote:
>> I use eSATA to test disk hot plug.
>> With previous 3 patches applied, disk hot plug does not wok
>> when ahci port/controller is runtime suspended.
>>
>> There are 2 cases we need to handle for hot plug:
>>
>> 1. port suspended, controller active
>>    Is IRQ need to be enabled for port to detect hot plug?
>>
>> 2. port suspended, controller suspended
>>    Will controller get a PME when hot plug happens?
>>
>> I'm still investigating hot plug support.
>>
>> Anyone has comment?
>
> SATA link detection requires hot wire and keeping wire hot takes
> power.

Oh, hardware in general just sucks. :)

> I think it's fair tradeoff to not support hotplug while
> powersaving is on.  We have warm plug mechanism (the SCSI rescan
> trigger via sysfs) after all.  It would be nice if things like that is
> somehow exported to userland in easy way tho (cc'ing Kay), but I
> frankly don't have much idea where that would fit.

Getting David in the loop. He might have an idea.

Kay
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