powerpc: Enable sparse irq_descs on powerpc

Defining CONFIG_SPARSE_IRQ enables generic code that gets rid of the
static irq_desc array, and replaces it with an array of pointers to
irq_descs.

It also allows node local allocation of irq_descs, however we
currently don't have the information available to do that, so we just
allocate them on all on node 0.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 3aa79f8e39e4..61abde11a45e 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -377,6 +377,19 @@ config IRQ_ALL_CPUS
 	  CPU.  Generally saying Y is safe, although some problems have been
 	  reported with SMP Power Macintoshes with this option enabled.
 
+config SPARSE_IRQ
+	bool "Support sparse irq numbering"
+	default y
+	help
+	  This enables support for sparse irqs. This is useful for distro
+	  kernels that want to define a high CONFIG_NR_CPUS value but still
+	  want to have low kernel memory footprint on smaller machines.
+
+	  ( Sparse IRQs can also be beneficial on NUMA boxes, as they spread
+	    out the irq_desc[] array in a more NUMA-friendly way. )
+
+	  If you don't know what to do here, say Y.
+
 config NUMA
 	bool "NUMA support"
 	depends on PPC64