linux-kernel - Re: [RFC PATCH v2 8/8] [SCSI] sr: check and enable Zero-power ODD support

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Date:	Sat, 03 Mar 2012 11:05:21 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Aaron Lu <aaron.lu@....com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Zhang Rui <rui.zhang@...el.com>,
	Jeff Garzik <jgarzik@...ox.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Tejun Heo <tj@...nel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	linux-ide@...r.kernel.org,
	SCSI development list <linux-scsi@...r.kernel.org>,
	Linux-pm mailing list <linux-pm@...r.kernel.org>,
	linux-acpi <linux-acpi@...r.kernel.org>
Subject: Re: [RFC PATCH v2 8/8] [SCSI] sr: check and enable Zero-power ODD
 support

On Fri, 2012-03-02 at 23:08 +0800, Aaron Lu wrote:
> Hi,
> 
> On Fri, Mar 2, 2012 at 3:02 PM, Lin Ming <ming.m.lin@...el.com> wrote:
> > On Thu, 2012-03-01 at 11:02 -0500, Alan Stern wrote:
> >> On Thu, 1 Mar 2012, Lin Ming wrote:
> >>
> >> > ZPODD(Zero Power Optical Disk Drive) is a new feature in
> >> > SATA 3.1 specification. It provides a way to power off unused ODD.
> >> >
> >> > ZPODD support is checked in in sr_probe().
> >> > can_power_off flag is set during suspend if ZPODD is supported.
> >> >
> >> > ATA port's runtime suspend callback will actually power off the ODD
> >> > and its runtime resume callback will actually power on the ODD.
> >> >
> >> > When ODD is powered off(D3Cold state), inserting disk will trigger a
> >> > wakeup event(GPE). GPE AML handler notifies the associated device. Then
> >> > ODD is resumed in the notify handler.
> >>
> >> I have one stylistic comment on this patch...
> >>
> >> > diff --git a/drivers/scsi/sr.h b/drivers/scsi/sr.h
> >> > index 37c8f6b..39b3d8c 100644
> >> > --- a/drivers/scsi/sr.h
> >> > +++ b/drivers/scsi/sr.h
> >> > @@ -42,6 +42,9 @@ typedef struct scsi_cd {
> >> >     unsigned readcd_cdda:1; /* reading audio data using READ_CD */
> >> >     unsigned media_present:1;       /* media is present */
> >> >
> >> > +   unsigned zpodd:1;       /* is ZPODD supported */
> >> > +   unsigned zpodd_event:1;
> >> > +
> >>
> >> You should not expect your readers to understand what "ZPODD" means.
> >> drivers/scsi/sr.h is used by lots of different people, many of whom
> >> will have no idea what it refers to, especially since it is part of
> >> the SATA spec and not the SCSI spec.  You should provide a brief
> >> explanation.
> >
> > I'll add some explanation.
> >
> > But I'm thinking maybe it's better to move this flag to ata layer, for
> 
> Agree.
> 
> > example, adding a flag to libata.h
> >
> > ATA_DFLAG_ZPODD
> >
> 
> How about ATA_DFLAG_DA(device attention)?

Yes, it's better.

> It follows the name used in the sata spec and this feature might have
> other uses in the future in addition to zero power odd(just my wild guess).
> 
> > sr runtime pm is only enabled when ZPODD(or more general, power off) is
> > supported.
> > So the problem is how will sr driver know this flag?
> >
> 
> What about adding a new field to scsi_device to reflect this capability of
> the underlying sata device? We can then set this field in ata_scsi_scan_host.

Nice idea.

I'll refresh this patch.

Thanks,
Lin Ming

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