PNP: do not stop/start devices in suspend/resume path

[Bjorn Helgaas <bjorn.helgaas@hp.com>]

On Wednesday 05 December 2007 11:24:18 am Bjorn Helgaas wrote:
> Re: warning on suspend-to-RAM caused by
> pnp-request-ioport-and-iomem-resources-used-by-active-devices.patch,
> thread here: http://lkml.org/lkml/2007/11/22/110
> 
> On Saturday 01 December 2007 05:00:34 am Jiri Slaby wrote:
> > I didn't get it. Maybe some trolls poking around or something (maybe the
> > ext3 breakage which fsck fixed). It works after recompilation of the
> > whole tree. And the important part -- the warning has gone.
> 
> Good.  It's not clear to me whether it is safe to leave devices
> enabled while we sleep.  I don't see an actual problem, but there
> might be something related to hotplug while we're asleep or something.
> So I'll cc: some additional people who might have some insight.

I checked with a Windows kernel person, who said that when preparing
to sleep, Windows puts devices in S3 state (I think he meant D3)
and does not use _DIS.

I think this patch is the right thing to do.  It's possible we'll
trip over some BIOS issue, but in the long term, we should try to
do it the same way Windows does.  Andrew, can you add this before
pnp-request-ioport-and-iomem-resources-used-by-active-devices.patch?

Thanks,
  Bjorn


PNP: do not stop/start devices in suspend/resume path

Do not disable PNP devices in the suspend path.  We still call
the driver's suspend method, which should prevent further use of
the device, and the protocol suspend method, which may put the
device in a low-power state.

I'm told that Windows puts devices in a low-power state (Linux
does this in the protocol suspend method), but does not use _DIS
in the suspend path.  Other relevant references:

  - In the ACPI 3.0b spec, I can't find any mention of _DIS in
    connection with sleep.  And Device Object Notifications,
    Section 5.6.3, Table 5-43, says we should get a bus check
    after awakening if hardware was removed while we slept.

  - This: http://msdn2.microsoft.com/en-us/library/ms810079.aspx
    makes a similar point about how the OS re-enumerates devices
    as a result of a power state change (3rd last paragraph of
    text).

  - This: http://msdn2.microsoft.com/en-us/library/aa489874.aspx
    suggests that Windows only stops a device to rebalance hardware
    resources.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>

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;
-	}
-
 	if (pnp_drv->resume)
 		return pnp_drv->resume(pnp_dev);