Re: acpi-20040715: functional regression on ASUS M2N

[Nate Lawson <nate-Y6VGUYTwhu0@public.gmane.org>]

Matthew Garrett wrote:
> On Thu, 2004-08-05 at 14:49 -0400, Nathan Bryant wrote:
>>The ELCR save/restore patch is causing regressions for some people. What 
>>if the problem is that we're saving/restoring registers at the wrong time?
> 
> 
> On closer investigation, I found that the system was restoring my ioapic
> state /after/ it had started the programmable interrupt timer back up.
> Changing line 310 of drivers/base/sys.c to list_for_each_entry_reverse
> seems to have greatly improved my ability to suspend and resume (which
> worked fine before the interrupt controller suspend/resume patches,
> except that I didn't get many interrupts...) 
> 
> There doesn't seem to be any fine-grained way to control the order of
> suspend/resume for individual drivers. It seems to be assumed that
> everything that devices depend on will be higher than them in the tree,
> and so everything will "just work" - I'm not sure this is true. As
> another example, I just had my wireless card fail to resume correctly.
> It tried to do a hotplug firmware load on resume. Which was difficult,
> because it was resumed before the IDE interface was. How can this sort
> of thing be avoided?

With a real device framework.  We (FreeBSD) propagate suspend requests 
throough our generic device structure.  Each parent and child has a 
method which can be overridden.  This starts at the root and is 
propagated downward.

For instance, the PCI driver has methods that save/restore BARs:
         DEVMETHOD(device_suspend,       pci_suspend),
         DEVMETHOD(device_resume,        pci_resume),

The suspend function does its work and then calls bus_generic_suspend() 
which propagates the request down to the children.  Or if it knows that 
it needs to run after all children have suspended, it calls 
bus_generic_suspend() first, then does its work.

/**
  * @brief Helper function for implementing DEVICE_SUSPEND()
  *
  * This function can be used to help implement the DEVICE_SUSPEND()
  * for a bus. It calls DEVICE_SUSPEND() for each of the device's
  * children. If any call to DEVICE_SUSPEND() fails, the suspend
  * operation is aborted and any devices which were suspended are
  * resumed immediately by calling their DEVICE_RESUME() methods.
  */
int
bus_generic_suspend(device_t dev)
{
         int             error;
         device_t        child, child2;

         TAILQ_FOREACH(child, &dev->children, link) {
                 error = DEVICE_SUSPEND(child);
                 if (error) {
                         for (child2 = TAILQ_FIRST(&dev->children);
                              child2 && child2 != child;
                              child2 = TAILQ_NEXT(child2, link))
                                 DEVICE_RESUME(child2);
                         return (error);
                 }
         }
         return (0);
}

The key helpful thing is that each driver can specify its own methods 
through its device object but they can be called in a generic way.  For 
instance, if the root bus does "device_suspend(pci_dev)", then the 
actual function call expanded at run time is "pci_suspend(pci_dev)"

-Nate


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