It turns out that at least some system device drivers need to allocate 
memory and/or sleep for one reason or another when either saving or 
restoring state. 

Instead of adding a 'level' paramter to the suspend() and resume() methods,
which I despise and think is a horrible programming interface, two new 
methods have been added to struct sysdev_driver:

        int     (*save)(struct sys_device *, u32 state);
        int     (*restore)(struct sys_device *);

that are called explicitly before and after suspend() and resume() 
respectively, with interrupts enabled. This gives the drivers the
flexibility to allocate memory and sleep, if necessary.