linux-kernel - Re: -mm: pnp-do-not-stop-start-devices-in-suspend-resume-path.patch breaks resuming isapnp cards

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Message-ID: <478E4A07.1050803@keyaccess.nl>
Date:	Wed, 16 Jan 2008 19:16:39 +0100
From:	Rene Herman <rene.herman@...access.nl>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
CC:	Jaroslav Kysela <perex@...ex.cz>, Andrew Morton <akpm@...l.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Pierre Ossman <drzeus@...eus.cx>, Pavel Machek <pavel@...e.cz>,
	Ondrej Zary <linux@...nbow-software.org>,
	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 16-01-08 18:46, Bjorn Helgaas wrote:

> On Tuesday 15 January 2008 12:51:35 am Jaroslav Kysela wrote:

>> 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?

Yes. The manual resource setting was recently removed from the ALSA drivers 
and I'd expect this can now go as a package-deal.

>> 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?

Yes.

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

Rene.
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