linux-kernel - Re: RFC: PNP: do not stop/start devices in suspend/resume path

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Date:	Mon, 10 Dec 2007 16:26:34 -0700
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	Jiri Slaby <jirislaby@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, matthew@....cx,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-pm@...ts.linux-foundation.org, drzeus@...eus.cx,
	linux-acpi@...r.kernel.org, Adam Belay <ambx1@....rr.com>,
	Matthieu Castet <castet.matthieu@...e.fr>,
	Len Brown <lenb@...nel.org>
Subject: Re: RFC: PNP: do not stop/start devices in suspend/resume path

On Friday 07 December 2007 12:13:35 am Shaohua Li wrote:
> On Thu, 2007-12-06 at 02:24 +0800, Bjorn Helgaas wrote:
> > Index: linux-mm/drivers/pnp/driver.c
> > ===================================================================
> > --- linux-mm.orig/drivers/pnp/driver.c  2007-11-30 13:58:25.000000000
> > -0700
> > +++ linux-mm/drivers/pnp/driver.c       2007-12-03 09:58:35.000000000
> > -0700
> > @@ -161,13 +161,6 @@
> >                         return error;
> >         }
> > 
> > -       if (!(pnp_drv->flags & PNP_DRIVER_RES_DO_NOT_CHANGE) &&
> > -           pnp_can_disable(pnp_dev)) {
> > -               error = pnp_stop_dev(pnp_dev);
> > -               if (error)
> > -                       return error;
> > -       }
> > -
> >         if (pnp_dev->protocol && pnp_dev->protocol->suspend)
> >                 pnp_dev->protocol->suspend(pnp_dev, state);
> >         return 0;
> > @@ -177,7 +170,6 @@
> >  {
> >         struct pnp_dev *pnp_dev = to_pnp_dev(dev);
> >         struct pnp_driver *pnp_drv = pnp_dev->driver;
> > -       int error;
> > 
> >         if (!pnp_drv)
> >                 return 0;
> > @@ -185,12 +177,6 @@
> >         if (pnp_dev->protocol && pnp_dev->protocol->resume)
> >                 pnp_dev->protocol->resume(pnp_dev);
> > 
> > -       if (!(pnp_drv->flags & PNP_DRIVER_RES_DO_NOT_CHANGE)) {
> > -               error = pnp_start_dev(pnp_dev);
> > -               if (error)
> > -                       return error;
> > -       }
> > -
> I'd suggest keep pnp_start_dev here to prevent BIOS not or assign
> different resources after a resume.

The patch I currently have in -mm (http://lkml.org/lkml/2007/10/29/412)
merely requests resources in pnp_start_dev() and releases them in
pnp_stop_dev().  So if we remove pnp_stop_dev() but keep pnp_start_dev(),
I have to fix that patch to deal with things that may already be
reserved.

But I don't see any mention in the spec of running _SRS in the
sleep/wakup path, so I'm not convinced it's really necessary.
Section 7.4 mentions _TTS, _PTS, _GTS, etc., but not _SRS.

For devices, it looks like the intent is that BIOS should generate
notifications that cause OSPM to re-enumerate devices that might
have changed.  I'm pretty sure Linux is missing some of that code,
though, so I could believe that _SRS might help paper over that
deficiency.

What I'd really like to do is figure out how Windows uses _SRS and
do the same thing.

Bjorn
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