linux-kernel - Re: [PATCH] Re: NAK new drivers without proper power management?

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Message-Id: <1171234145.4493.91.camel@nigel.suspend2.net>
Date:	Mon, 12 Feb 2007 09:49:05 +1100
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	Willy Tarreau <w@....eu>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Daniel Barkalow <barkalow@...ervon.org>,
	Robert Hancock <hancockr@...w.ca>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jeff Garzik <jeff@...zik.org>, Pavel Machek <pavel@....cz>,
	pm list <linux-pm@...ts.osdl.org>
Subject: Re: [PATCH] Re: NAK new drivers without proper power management?

Hi.

On Sun, 2007-02-11 at 12:13 +0000, Matthew Garrett wrote:
> On Sun, Feb 11, 2007 at 07:54:04AM +0100, Willy Tarreau wrote:
> 
> > instead of modifying all drivers to explicitly state that they don't support
> > it, we should start with a test of the NULL pointer for .suspend which should
> > mean exactly the same without modifying the drivers. I find it obvious that
> > a driver which does provide a suspend function will not support it. And if
> > some drivers (eg /dev/null) can support it anyway, it's better to change
> > *those* drivers to explicitly mark them as compatible.
> 
> No, that doesn't work. In the absence of suspend/resume methods, the PCI 
> layer will implement basic PM itself. In some cases, this works. In 
> others, it doesn't. There's no way to automatically determine which is 
> which without modifying the drivers.

I think we have it backwards there. Power management support for a
driver should always start with the driver itself. If there's a generic
routine that can be used for the bus, the driver should explicitly set
the routine to the generic routine.

Regards,

Nigel

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