On 30/07/15 10:30, Jon Hunter wrote:

On 30/07/15 10:04, Marc Zyngier wrote:

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On 30/07/15 09:33, Jon Hunter wrote:

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On 30/07/15 09:20, Marc Zyngier wrote:

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On 29/07/15 20:27, Jon Hunter wrote:

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On 29/07/15 19:33, Russell King - ARM Linux wrote:

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On Wed, Jul 29, 2015 at 03:43:04PM +0100, Jon Hunter wrote:

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The gic_init_bases() function initialises an array that stores the mapping
between the GIC and CPUs. This array is a global array that is
unconditionally initialised on every call to gic_init_bases(). Although,
it is not common for there to be more than one GIC instance, there are
some devices that do support nested GIC controllers and gic_init_bases()
can be called more than once.

A 2nd call to gic_init_bases() will clear the previous CPU mapping and
will only setup the mapping again for CPU0. This is because for child GIC
controllers there is most likely only one recipient of the interrupt.

Fix this by moving the CPU mapping array to the GIC chip data structure
so that it is initialised for each GIC instance separately. It is assumed
that the bL switcher code is only interested in the root or primary GIC
instance.

Does it make sense to expose the per-CPU-ness of the non-primary GIC?
If they are chained off a primary GIC SPI interrupt, then all IRQs on
the secondary GIC are routed to the same CPU that the SPI on the primary
GIC is routed to.

I am looking at a use-case where there is a secondary GIC and the secondary
GIC is used as a interrupt router between the main CPU cluster and another
CPU. So in this case the mapping of a secondary is still of interest. This
patch does not address setting up the secondary mapping, but avoids a
secondary GIC overwriting the primary map (which we don't want).
 

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Other features like the PPIs and SGIs in the secondary CPU should also
be ignored - they probably aren't used anyway.

Yes, agree.
 

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I have to say though... are the 1020 IRQs that the primary GIC provides
really not enough?  What insane hardware needs more than 1020 IRQs?

Ha. I guess some realview boards for a start ...

# grep -r "gic_init(1" arch/arm/
arch/arm/mach-realview/realview_pb1176.c:	gic_init(1, IRQ_PB1176_GIC_START,
arch/arm/mach-realview/realview_eb.c:		gic_init(1, 96, __io_address(REALVIEW_EB_GIC_DIST_BASE),
arch/arm/mach-realview/realview_pb11mp.c:	gic_init(1, IRQ_PB11MP_GIC_START,

Different use case. These are development boards with a relatively
modular design, where the SoC may or may not have a GIC by itself. When
it has one, you end up with the on-board GIC being a secondary one.

Yes, I understand that the use-case may be different, but I highlighted
this as a use where the primary map would be overwritten as the driver
is today.

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I never thought someone would quote these designs as an example to
follow... ;-)

I can't say if this example was followed, but nevertheless hardware
designers certainly do get creative ;-)

So we need to ensure the primary cpu map does not get overwritten by a
secondary and I have a case where the secondary map is of interest. So
are ok with this?

My point is that there is no secondary map. That map should only be
written for the primary GIC, because that's the only place it makes
sense. Your "other CPU" is not under the control of Linux (at least, not
as a CPU), so this map is not the right data structure.

Yes the "other CPU" may not run Linux, but it is certainly under the
control of Linux as a slave CPU. Linux will decide whether it wants to
receive the interrupts from this GIC or route them to the other CPU.

Yes, I see that this may not be technically a cpu map and may be that is
a mis-use. Following that I assume that using set_affinity here would
also not be correct and a custom API should be employed?

Indeed. set_affinity is only concerned with delivering interrupts to the
CPUs, and not to other entities. It looks like we need an different API,
but I would refrain from declaring it "custom". There is at least one
other example of a platform doing similar things (vybrid), and I'd like
to see some collaboration on that (Stefan on CC).

If that is the case, then may be I should just fix up the irq-gic driver
to only set the cpu map for the primary?

Yes please.

	M.
-- 
Jazz is not dead. It just smells funny...