linux-kernel - Re: [PATCH v3 7/7] [SCSI] sr: adds Zero-power ODD support

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Date:	Fri, 30 Mar 2012 10:28:23 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Aaron Lu <aaron.lu@....com>
cc:	Lin Ming <ming.m.lin@...el.com>, Zhang Rui <rui.zhang@...el.com>,
	Jeff Garzik <jgarzik@...ox.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Tejun Heo <tj@...nel.org>,
	<linux-kernel@...r.kernel.org>, <linux-ide@...r.kernel.org>,
	<linux-scsi@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	linux-acpi <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v3 7/7] [SCSI] sr: adds Zero-power ODD support

On Fri, 30 Mar 2012, Aaron Lu wrote:

> > > For the ODD to be put into suspend state, the conditions should be:
> > > 1 tray closed
> > > 2 no media inside
> > > I think we missed the condition 1 check now.
> > > 
> > > And if we follow the two conditions, the events can be safely ignored.
> > 
> > No, they can't.  Otherwise the device won't power back up when the user 
> > inserts a new disc.
> > 
> 
> The ODD is put to zero power state, so it can't react to the eject
> button without being powered up back first ;-)
> On current implementation, ACPI is used to power back up the ODD like this:
> 1 User press the eject button;
> 2 A gpe event fired, and ACPI interrupt, and the corresponding gpe
> handler runs and the ODD's ACPI handle is notified about DEVICE_WAKE_UP;
> 3 In ODD's acpi notify handler, we power back up it by scsi_autopm_get_device.
> This is handled in the following Lin Ming's patch:
> [PATCH v3 2/7] libata-acpi: add ata port runtime D3Cold support

I see.  Then you are right; it's not necessary to check for events 
while the drive is at zero power.

> When the ODD is put to zero power state, it will not be able to handle
> commands like CDROMEJECT. We have to power it up first and then handle
> the ioctl request. Currently, we only power back up the ODD when user
> press the eject button as explained above.

Then you may want to avoid going to zero-power while a program is
holding the device file open.  After all, the program might issue a
CDROMEJECT ioctl.

Alan Stern

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