[PATCH 03/17] ARM: gic: Use cpu pm notifiers to save gic state

[Colin Cross]

On Sat, Jul 9, 2011 at 3:33 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Sat, Jul 09, 2011 at 03:10:56PM -0700, Colin Cross wrote:
>> This is necessary for cpuidle states that lose the GIC registers, not
>> just suspend, because the GIC is in the cpu's power domain.  We could
>> avoid saving and restoring all the GIC registers in suspend and idle
>> by reusing the initialization functions, and then having the core irq
>> code call the unmask, set_type, and set_affinity functions on each irq
>> to reconfigure it, but that will be very inefficient - it will convert
>> each register write in the restore functions to a read-modify-write
>> per interrupt in that register.  Santosh is already complaining that
>> this commong GIC restore code will be slower than the automatic DMA to
>> restore the GIC registers that OMAP4 supports.
>
> Well, we need to come up with something sensible - a way of doing this
> which doesn't require every interrupt controller driver (of which we as
> an architecture have many) to have lots of support added.
>
> If the current way is inefficient and is noticably so, then let's talk
> to Thomas about finding a way around that - maybe having the generic
> code make one suspend/resume callback per irq gc chip rather than doing
> it per-IRQ.  We can then reuse the same paths for suspend/resume as for
> idle state saving.
>

Are you referring to moving the gic driver to be gc chip?  Otherwise,
I don't understand your suggestion - how is callback per chip any
different than what this patch implements?  It just gets it's
notification through a cpu_pm notifier, which works in idle and
suspend, instead of a syscore op like the gc driver does.

This patch does save and restore some registers that are never
modified after init, so they don't need to be saved.