[PATCH] ARM: ux500: Initialize irq affinity

[Will Deacon]

Hi Linus,

On Fri, Jan 20, 2012 at 03:45:40PM +0000, Linus Walleij wrote:
> On Fri, Jan 20, 2012 at 2:03 PM, Russell King - ARM Linux
> <linux at arm.linux.org.uk> wrote:
> > On Fri, Jan 20, 2012 at 01:59:16PM +0100, Per Fransson wrote:
> >> Use irq_set_affinity() to initialize the kernel view of irq affinity
> >> when programming the GIC registers.
> >
> > Why is this necessary?
> 
> Necessary: we don't quite know. (Maybe should have been RFC, but
> this patch is better than being silent of it...)
> 
> On the Ux500 all shared peripheral IRQs (32 thru 127) are delivered
> to CPU0 (hardwired, will not work on CPU1), I have heard that this
> is sort of what everybody does but don't know for sure. (Marc?)

Oo-er, I've not heard of any platforms doing this before, but it is
permitted by the GIC spec so we should deal with it.

> Currently the gic_set_affinity() in common/gic.c isn't called for any
> IRQs so they are left in their power-on state (from U-Boot or
> similar) which is essentially correct (we checked dumps of the
> registers).
> 
> However when we look at the irq descriptors in e.g. crash:
> 
>     crash> irq -s
>     IRQ NAME                 AFFINITY
>      36 Nomadik Timer Tick   0
>      43 uart-pl011           0-1
>      44 nmk-i2c              0-1
>      46 pl022                0-1
>      53 nmk-i2c              0-1
>      54 nmk-i2c              0-1
>     (... etc ...)
> 
> So the descriptors think the IRQs are shared except for the
> timer. Which isn't true. So this patch makes the map match
> reality.

Right. So these are SPIs that are configured statically in hardware. They
should therefore be identifiable by writing zeros to the ICDIPTRn registers
at the distributor and then reading back to see if any of the bits are set.
If they are, we can create a cpumask for each interrupt and set the affinity
to that.

The next question is, is gic_dist_init the right place to do this or is it
too early (we need to update the irq_desc)?

> > And if it is necessary, why do you think it
> > should be ux500 specific?
> 
> Good question. If this is the case for all SMP gic users maybe we
> should make the code #ifdef CONFIG_SMP inside gic.c instead?
> (Sans the check for the modem IRQs, they should probably also
> be made affine to CPU0.)

Although I think you're the only platform doing this, we should aim to
handle it in the GIC driver at some initialisation stage.

Will