Re: pci_restore_state

[Andrew Morton <akpm@osdl.org>]

On Sun, 04 Jun 2006 06:13:30 -0400
Ryan Lortie <desrt@desrt.ca> wrote:

> Currently pci_restore_state() (drivers/pci/pci.c) restores the PCI state
> by copying in the saved PCI configuration space, a dword at a time,
> starting from 0 up to 15.
> 
> This causes a crash when my Macbook resumes from sleep (specifically,
> when restoring the configuration space of the PCI bridge).
> 
> Reading the PCI specification, the register at dword 1 (ie: bytes 4-7)
> is split half and half between status and command words.  The command
> word effectively controls the way which the PCI device interacts with
> the system.  If it is 0, the device is logically disconnected from the
> bus (PCI Local Bus Specification Revision 2.2, 6.2.2 "Device
> Control").  
> 
> When a device first powers up, the command register value is normally
> zero (and is zero in my specific case).
> 
> The problem with the way that the PCI state is currently restored is
> that the write to the command register logically reconnects the device
> to the bus before the rest of the configuration space has been filled
> in.
> 
> My Macbook crashes on resume.
> 
> If I reverse the for loop to start from 15 and count down to 0, then the
> majority of the configuration space is filled in _before_ the command
> word is modified.  No crash.

We have a patch pending which will do that.

http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/gregkh-03-pci/pci-reverse-pci-config-space-restore-order.patch

The present plan will be to get this into 2.6.18.