Date:	Wed, 16 Jan 2008 19:03:23 +0100
From:	Ondrej Zary <linux@...nbow-software.org>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
Cc:	Jaroslav Kysela <perex@...ex.cz>,
	Rene Herman <rene.herman@...access.nl>,
	Andrew Morton <akpm@...l.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Pierre Ossman <drzeus@...eus.cx>, Pavel Machek <pavel@...e.cz>,
	ALSA development <alsa-devel@...a-project.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Takashi Iwai <tiwai@...e.de>,
	linux-pm@...ts.linux-foundation.org
Subject: Re: -mm: pnp-do-not-stop-start-devices-in-suspend-resume-path.patch breaks resuming isapnp cards

On Wednesday 16 January 2008 18:46:03 Bjorn Helgaas wrote:
> On Tuesday 15 January 2008 12:51:35 am Jaroslav Kysela wrote:
> > On Mon, 14 Jan 2008, Bjorn Helgaas wrote:
> > > On Saturday 12 January 2008 11:13:35 pm Rene Herman wrote:
> > > > ... And, now that I have your attention, while it's
> > > > not important to the issue anymore with the tests removed as the
> > > > submitted patch did, do you have an opinion on (include/linux/pnp.h):
> > > >
> > > > /* pnp driver flags */
> > > > #define PNP_DRIVER_RES_DO_NOT_CHANGE    0x0001  /* do not change the
> > > > state of the device */
> > > > #define PNP_DRIVER_RES_DISABLE          0x0003  /* ensure the device
> > > > is disabled */
> > > >
> > > > I find DISABLE including DO_NOT_CHANGE rather unexpected...
> > >
> > > I don't know the history of those flags, but I wish they didn't exist.
> >
> > Ok, something to explain. These flags exists to allow drivers to
> > manually configure (override) PnP resources at init time - we know - for
> > example in ALSA - that some combinations simply does not work for all
> > soundcards.
> >
> > The DISABLE flags simply tells core PnP layer - driver will handle
> > resource allocation itself, don't do anything, just disable hw physically
> > and do not change (allocate) any resources. Value 0x03 is valid in this
> > semantics.
>
> It looks like sound drivers use PNP_DRIVER_RES_DISABLE to say "ignore
> what PNP tells us about resource usage and we'll just use the compiled-
> in or command-line-specified resources".
>
> The main reason to do that would be to work around BIOS defects or
> to work around deficiencies in the Linux PNP infrastructure (e.g.,
> maybe we erroneously place another device on top of the sound card
> or something).
>
> I'm just suspicious because PNP_DRIVER_RES_DISABLE is only used in
> sound drivers.  If it's to work around BIOS defects, why wouldn't
> other PNP drivers need it sometimes, too?  And wouldn't it be better
> to use PNP quirks for BIOS workarounds?
>
> > Unfortunately, suspend / resume complicates things a bit, but PnP core
> > can handle DO_NOT_CHANGE flag. But it will just mean - _preserve_
> > resource allocation from last suspend state for this device and enable hw
> > physically before calling resume() callback.
>
> When resuming, wouldn't we *always* want to preserve the resource
> allocation from the last suspend, regardless of whether
> PNP_DRIVER_RES_DO_NOT_CHANGE is specified?

I'd say yes. If base address of a card changes, driver will break.

I grepped drivers for these flags too - to find out what they do (or should 
do?) - but failed to find out anything useful.

> Linux PNP definitely has issues with suspend/resume, and I suspect
> this is one of them.
>
> Bjorn
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-- 
Ondrej Zary
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