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

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Date:	Sun, 11 Feb 2007 14:09:43 +0100
From:	Willy Tarreau <w@....eu>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Daniel Barkalow <barkalow@...ervon.org>,
	nigel@...el.suspend2.net, 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?

On Sun, Feb 11, 2007 at 12:13:40PM +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.

Then change the PCI layer to do the basic PM only for known compatible
drivers, and modify only the known-compatible drivers to mark them
explicitly compatible. IMHO, it generally is a bad idea to require that
any driver explicitly states what it *does not* support. It's the reason
why users encounter problem on new features with old drivers. For instance,
do you know if the old ISA NE2000 driver breaks suspend ? I don't know,
but I would at least expect it not to support it by default. It's best
to announce what *is* supported and consider everything unimplemented
otherwise explicitly stated.

Regards,
Willy

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