Re: RFC, GIC based smp_cross_call cleanup suggestion

Santosh Shilimkar
2011-04-03T06:23:25Z

+ Thomas G,

On 4/2/2011 2:40 PM, Colin Cross wrote:
> On Sat, Apr 2, 2011 at 1:51 AM, Russell King - ARM Linux
> <linux@arm.linux.org.uk> wrote:
>> On Fri, Apr 01, 2011 at 04:55:02PM -0600, Grant Likely wrote:
>>> On Fri, Apr 1, 2011 at 4:26 PM, John Linn<John.Linn@xilinx.com> wrote:
>>>> I’m getting ready to submit a patch to add SMP to Xilinx code. I notice that
>>>> smp_cross_call for all GIC based platforms is duplicated across each
>>>> platform in smp.h.
>>>>
>>>>
>>>>
>>>> I thought I’d try to jump in to help with some cleanup, although I realize
>>>> it’s minimal, I have to start somewhere.
>>>>
>>>>
>>>>
>>>> What about moving the smp_cross_call for GIC based designs into gic.h?
>>>
>>> Go for it. It's an obvious cleanup.
>>
>> That assumes that all SMP implementations will always have a GIC. It
>> looks to me like this is conditional on shmobile, and so I don't think
>> its that trivial - maybe Paul or Magnus can first indicate why this is.
>
> OMAP4 may also require a custom smp_cross_call implementation if CPU
> idle is going to be supported in SMP - in CPU off idle modes, a GIC
> SGI will not wake the CPU, and a write directly to the CPU's power
> management controller or an external interrupt source would be
> required.

This can be done without making smp_cross_call() platform
specific.
While working on broad-cast notifiers for ARM with Thomas G, this
point was discussed.

Where the TWD can't wakeup its own local CPU from C3 mode, how do we
provide a platform specific method to perform this wakeup ?

Thomas Quoted....
"It would not complicate the OMAP code that much. All it needs is
extending the clock event device callbacks by an broadcast_affinity()
function which would be called from the broadcast code when the
broadcast device is armed. The argument would be a cpumask which would
tell you which core(s) to wake up when the broadcast timer fires next.

So OMAP would fill in that hook and implement the wakeup redirector
setup, which I guess would be a couple of lines."

From above it's should be trivial once the broad-cast notifiers
are extended to have "broadcast_affinity()" supported

Regards
Santosh

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