From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Zhang Rui <rui.zhang@intel.com>
Subject: Re: [RFC PATCH 4/6] PM / Runtime: Introduce flag can_power_off
Date: Tue, 14 Feb 2012 23:38:13 +0100
User-Agent: KMail/1.13.6 (Linux/3.3.0-rc3+; KDE/4.6.0; x86_64; ; )
Cc: Alan Stern <stern@rowland.harvard.edu>, Lin Ming <ming.m.lin@intel.com>,
        Jeff Garzik <jgarzik@pobox.com>, Tejun Heo <tj@kernel.org>,
        Len Brown <lenb@kernel.org>, linux-kernel@vger.kernel.org,
        linux-ide@vger.kernel.org, linux-scsi@vger.kernel.org,
        linux-pm@vger.kernel.org
References: <Pine.LNX.4.44L0.1202131534040.11382-100000@iolanthe.rowland.org> <1329203489.19384.39.camel@rui.sh.intel.com>
In-Reply-To: <1329203489.19384.39.camel@rui.sh.intel.com>
MIME-Version: 1.0
Content-Type: Text/Plain;
  charset="utf-8"
Content-Transfer-Encoding: 8BIT
Message-Id: <201202142338.13516.rjw@sisk.pl>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2729
Lines: 62

On Tuesday, February 14, 2012, Zhang Rui wrote:
> Hi, Alan,
> 
> On 一, 2012-02-13 at 15:41 -0500, Alan Stern wrote:
> > On Mon, 13 Feb 2012, Rafael J. Wysocki wrote:
> > 
> > > > I'm not sure if this is really the right approach.  What you're trying 
> > > > to do is implement two different low-power states, basically D3hot and 
> > > > D3cold.  Currently the runtime PM core doesn't support such things; all 
> > > > it knows about is low power and full power.
> > > 
> > > I'd rather say all it knows about is "suspended" and "active", which mean
> > > "the device is not processing I/O" and "the device may be processing I/O",
> > > respectively.  A "suspended" device may or may not be in a low-power state,
> > > but the runtime PM core doesn't care about that.
> > 
> > Yes, okay.  We can say that this patch tries to implement two different 
> > "suspended" states, basically "low power" and "power off" (or D3hot and 
> > D3cold).
> > 
> Right!
> 
> > > > Before doing an ad-hoc implementation, it would be best to step back
> > > > and think about other subsystems.  Other sorts of devices may well have
> > > > multiple low-power states.  What's the best way for this to be
> > > > supported by the PM core?
> > > 
> > > Well, I honestly don't think there's any way they all can be covered at the
> > > same time and that's why we chose to support only "suspended" and "active"
> > > as defined above.  The handling of multiple low-power states must be
> > > implemented outside of the runtime PM core (like in the PCI core, for example).
> > 
> > That's the point.  If this is to be implemented outside of the runtime
> > PM core, should the patch be allowed to add new fields to struct
> > dev_pm_info (which has to be shared among all subsystems)?
> > 
> Surely it shouldn't in this case.
> 
> > Or to put it another way, if we do add new fields to struct dev_pm_info
> > (like can_power_off) in order to help support multiple "suspended"  
> > states, shouldn't these new fields be such that they can be used by
> > many different subsystems rather than being special for the
> > full-power/no-power situation?
> > 
> My opinion is that the concept of "no-power state" is unique for all
> devices/buses/platforms.

No, it is not, basically because of power domains.  If they are used,
then individual device power states are not well defined at all.

> If any of them support this, they can use the routines without any
> confusion.

No, they can't.

Thanks,
Rafael
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/