From: Matthew Garrett <mjg59@srcf.ucam.org>
To: "Jeffrey W. Baker" <jwbaker@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Put unused PCI devices in D3
Date: Tue, 30 Sep 2008 01:09:23 +0100 [thread overview]
Message-ID: <20080930000923.GA29775@srcf.ucam.org> (raw)
In-Reply-To: <1222719064.19236.129.camel@squeak.gghcwest.com>
On Mon, Sep 29, 2008 at 01:11:03PM -0700, Jeffrey W. Baker wrote:
> Currently it looks to me from browsing the code that D3 is only used in
> Linux when the whole machine is headed for S3, and the drivers are asked
> to suspend. I think the drivers should be able to enter D3 in other
> circumstances:
>
> * During pci_unregister_driver ... i.e. on module unload
The fact that Linux isn't using a device doesn't inherently mean that
the system isn't using it. For example, the smbus controller will
probably still be used by ACPI even if there's no Linux driver loaded.
> * When a network interface is downed
Yes. Drivers are moving towards this model.
> * If the device is a bridge or hub with no downstream device
Potential problems with hotplugging? But sure, this kind of thing is
being implemented in USB and SCSI.
> * Whenever userspace requests D3 via sysfs
This functionality was explicitly removed a few years back.
> So, what fundamental problem prevents me from, for example, calling
> pci_set_power_state() from ohci1394's __exit?
Nothing I'm aware of. It sounds pretty safe in that case. But that would
require you to load and unload the driver - better to have the driver
loaded the entire time and make sure it does as much runtime power
management as possible. I don't know enough about the firewire OHCI
hardware, but can you power down most of the chip and still get hotplug
events?
--
Matthew Garrett | mjg59@srcf.ucam.org
next prev parent reply other threads:[~2008-09-30 0:09 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-09-29 20:11 Put unused PCI devices in D3 Jeffrey W. Baker
2008-09-30 0:09 ` Matthew Garrett [this message]
2008-09-30 0:55 ` Jeffrey W. Baker
2008-09-30 1:06 ` Matthew Garrett
2008-10-03 19:40 ` Pavel Machek
2008-10-03 19:37 ` Pavel Machek
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