Re: PCI PM: Restore standard config registers of all devices early

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Mon, 2009-02-02 at 16:28 -0800, Linus Torvalds wrote:
> 
> On Tue, 3 Feb 2009, Rafael J. Wysocki wrote:
> > 
> > BTW, on the PMAC the problematic driver appears to be the radeon driver,
> > according to Ben, and the breakage is not related to USB.
> 
> Hmm. atyfb_base.c has the same kind of things with magic PMAC code, but it 
> doesn't follow the USB pattern - it just replaces "pci_set_power_state()" 
> _entirely_. 
> 
> It seems a very interesting suspend routine, btw. It doesn't seem to do 
> any of the pci_save_state() at all, just re-initializes from scratch. 
> Maybe it is unhappy with the PM layer deciding to try to restore state 
> since it clearly didn't..

In fact, atyfb is also busted in -rc3 for different reasons though
probably by the same patch. I just dug an old powerbook with a mach64
and it crashes on resume with a machine check in there. (Among 2 or 3
other problems introduced by recent kernels, such as pci_get_* now
kmallocs with GFP_KERNEL internally which makes it WARN when I use it in
my low level suspend/resume code to whack the memory controller, etc...
this one is going to bite others I reckon, or IDE having some interrupt
problems on resume).

Adding a pci_save_state() to atyfb_pci_suspend() and a
pci_set_power_state() + pci_restore_state() at the beginning of
atyfb_pci_resume() fixes the machine check here.

Now where it gets funny is that I've added code to read the BAR and
command register content before, between, and after those calls and
print it and .. they are sane... Until i discovered that what happens is
that the new generic code seems to actually blast 0 all over my config
space if I don't call pci_save_state() in suspend(). I suppose I was
missing a "mandatory" call here... but the core should be more robust,
ie it shouldn't erase the config space of something because a driver
"forgot" to call pci_save_state() !

I'll do a patch fixing atyfb. I'll check if aty128fb tomorrow when
paulus brings a machine with such a chip in, but it looks like it will
have the same problem.

Cheers,
Ben.