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

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Message-ID: <CAOzJMDRTbq5o+jCyTtaAW_RPysfY3LhQ9gFC-tsvM8bsnh=rxQ@mail.gmail.com>
Date:	Fri, 2 Mar 2012 23:08:10 +0800
From:	Aaron Lu <aaron.lu@....com>
To:	Lin Ming <ming.m.lin@...el.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

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)?
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.

-Aaron
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