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

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Date:	Fri, 6 Apr 2012 14:13:23 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Aaron Lu <aaron.lu@....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 Thu, Apr 5, 2012 at 10:03 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Thu, 5 Apr 2012, Aaron Lu wrote:
>
>> Hi,
>>
>> On Thu, Apr 05, 2012 at 02:00:57PM +0800, Lin Ming wrote:
>> > >
>> > > Another thing to consider is, user might want to eject the tray by
>> > > software like the
>> > > eject /dev/sr0 command or some UI mouse clicks against the cdrom icon. I'm still
>> > > thinking how to do this correctly.
>> >
>> > Assume eject /dev/sr0 is implemented as:
>> >
>> > int fd = open("/dev/sr0", ...)
>> > ioctl(fd, CDROMEJECT)
>> >
>>
>> Indeed, it is implemented as this :-)
>>
>> > We may need to resume ODD in the ioctl handler(scsi_cmd_ioctl).
>> >
>>
>> I prefer we do this in sr_block_ioctl.
>> Suppose the ODD is now runtime suspended and received an ioctl:
>> if the ioctl's cmd is CDROMEJECT, resume it.
>> For other cases, return an error code like EPERM.
>> When done, according to the result of ioctl: if success, leave it resumed;
>> if failed, put it back to sleep.
>
> Alternatively, you may want to do the runtime resume in sr_open and
> sr_block_open and the suspend in the corresponding release routines.
> It's up to you.

GNOME opens cdrom every seconds to check status.
So we won't get the desired power savings if we do the runtime resume
in sr_block_open.
See my previous mail.

>
> Alan Stern
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