[PATCH v8 14/14] ARM: gic: add gic_ppi_map_on_cpu()

[Marc Zyngier]

On 11/07/11 12:38, Russell King - ARM Linux wrote:
> On Mon, Jul 11, 2011 at 12:14:36PM +0100, Marc Zyngier wrote:
>> And that's exactly what it does:
>> http://www.mail-archive.com/devicetree-discuss@lists.ozlabs.org/msg05026.html
>>
>> What I was trying to explain (and obviously failed to) is that the
>> _Linux_ DT _code_ will try to resolve the PPI number and convert it to a
>> _Linux_ IRQ number. Unless of course you don't encode it as an interrupt
>> at all, which seems to be what you're aiming for.
> 
> I'm not aiming for anything.  I'm trying to get you to fully understand
> the issue I've raised with your patches.  So, let's try a new scenario
> based on your statement above.
> 
> You have a device which happens to use a PPI.  You obtain its IRQ number
> from DT, which tells you IRQ 9, because the DT information said PPI 2
> CPU 1.  So you pass IRQ 9 into the IRQ request function, but as you're
> running on CPU 3, you have no access to the hardware for IRQ 9.
> 
> Please describe in detail how, with your patches, PPI 2 CPU 1 gets enabled
> rather than PPI 2 CPU 3 when IRQ 9 is requested.

You simply do not do that. You store the mapping for later use on the
right CPU. My code is buggy as I didn't think of the requesting thread
being preempted, but I never intended to do this sort of cross-CPU request.
-- 
Jazz is not dead. It just smells funny...