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>

5 files changed, 49 insertions, 13 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
diff --git a/arch/powerpc/include/asm/irq.h b/arch/powerpc/include/asm/irq.h
index 03dc28cdb4da..c85a32f1a17f 100644
--- a/arch/powerpc/include/asm/irq.h
+++ b/arch/powerpc/include/asm/irq.h
@@ -38,6 +38,9 @@ extern atomic_t ppc_n_lost_interrupts;
 /* Number of irqs reserved for the legacy controller */
 #define NUM_ISA_INTERRUPTS      16
 
+/* Same thing, used by the generic IRQ code */
+#define NR_IRQS_LEGACY          NUM_ISA_INTERRUPTS
+
 /* This type is the placeholder for a hardware interrupt number. It has to
  * be big enough to enclose whatever representation is used by a given
  * platform.
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 63e27d5c52de..eba53923630f 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -85,7 +85,10 @@ extern int tau_interrupts(int);
 #endif /* CONFIG_PPC32 */
 
 #ifdef CONFIG_PPC64
+
+#ifndef CONFIG_SPARSE_IRQ
 EXPORT_SYMBOL(irq_desc);
+#endif
 
 int distribute_irqs = 1;
 
@@ -613,8 +616,16 @@ void irq_set_virq_count(unsigned int count)
 static int irq_setup_virq(struct irq_host *host, unsigned int virq,
                             irq_hw_number_t hwirq)
 {
+        struct irq_desc *desc;
+
+        desc = irq_to_desc_alloc_node(virq, 0);
+        if (!desc) {
+                pr_debug("irq: -> allocating desc failed\n");
+                goto error;
+        }
+
         /* Clear IRQ_NOREQUEST flag */
-        irq_to_desc(virq)->status &= ~IRQ_NOREQUEST;
+        desc->status &= ~IRQ_NOREQUEST;
 
         /* map it */
         smp_wmb();
@@ -623,11 +634,14 @@ static int irq_setup_virq(struct irq_host *host, unsigned int virq,
 
         if (host->ops->map(host, virq, hwirq)) {
                 pr_debug("irq: -> mapping failed, freeing\n");
-                irq_free_virt(virq, 1);
-                return -1;
+                goto error;
         }
 
         return 0;
+
+error:
+        irq_free_virt(virq, 1);
+        return -1;
 }
 
 unsigned int irq_create_direct_mapping(struct irq_host *host)
@@ -1008,12 +1022,24 @@ void irq_free_virt(unsigned int virq, unsigned int count)
         spin_unlock_irqrestore(&irq_big_lock, flags);
 }
 
-void irq_early_init(void)
+int arch_early_irq_init(void)
 {
-        unsigned int i;
+        struct irq_desc *desc;
+        int i;
 
-        for (i = 0; i < NR_IRQS; i++)
-                irq_to_desc(i)->status |= IRQ_NOREQUEST;
+        for (i = 0; i < NR_IRQS; i++) {
+                desc = irq_to_desc(i);
+                if (desc)
+                        desc->status |= IRQ_NOREQUEST;
+        }
+
+        return 0;
+}
+
+int arch_init_chip_data(struct irq_desc *desc, int node)
+{
+        desc->status |= IRQ_NOREQUEST;
+        return 0;
 }
 
 /* We need to create the radix trees late */
diff --git a/arch/powerpc/kernel/ppc_ksyms.c b/arch/powerpc/kernel/ppc_ksyms.c
index c8b27bb4dbde..07115d6cd4ba 100644
--- a/arch/powerpc/kernel/ppc_ksyms.c
+++ b/arch/powerpc/kernel/ppc_ksyms.c
@@ -162,7 +162,6 @@ EXPORT_SYMBOL(screen_info);
 
 #ifdef CONFIG_PPC32
 EXPORT_SYMBOL(timer_interrupt);
-EXPORT_SYMBOL(irq_desc);
 EXPORT_SYMBOL(tb_ticks_per_jiffy);
 EXPORT_SYMBOL(cacheable_memcpy);
 EXPORT_SYMBOL(cacheable_memzero);
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 04f638d82fb3..fd785f7a279b 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -356,11 +356,6 @@ void __init setup_system(void)
          */
         initialize_cache_info();
 
-        /*
-         * Initialize irq remapping subsystem
-         */
-        irq_early_init();
-
 #ifdef CONFIG_PPC_RTAS
         /*
          * Initialize RTAS if available