powerpc: iSeries has only 256 IRQs

The iSeries Hypervisor only allows us to specify IRQ numbers up to 255 (it
has a u8 field to pass it in).  This patch allows platforms to specify a
maximum to the virtual IRQ numbers we will use and has iSeries set that
to 255.  If not set, the maximum is NR_IRQS - 1 (as before).

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

1 files changed, 22 insertions, 14 deletions

diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index bb5c9501234c..57d560c68897 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -272,18 +272,26 @@ unsigned int virt_irq_to_real_map[NR_IRQS];
  * Don't use virtual irqs 0, 1, 2 for devices.
  * The pcnet32 driver considers interrupt numbers < 2 to be invalid,
  * and 2 is the XICS IPI interrupt.
- * We limit virtual irqs to 17 less than NR_IRQS so that when we
- * offset them by 16 (to reserve the first 16 for ISA interrupts)
- * we don't end up with an interrupt number >= NR_IRQS.
+ * We limit virtual irqs to __irq_offet_value less than virt_irq_max so
+ * that when we offset them we don't end up with an interrupt
+ * number >= virt_irq_max.
  */
 #define MIN_VIRT_IRQ    3
-#define MAX_VIRT_IRQ    (NR_IRQS - NUM_ISA_INTERRUPTS - 1)
-#define NR_VIRT_IRQS    (MAX_VIRT_IRQ - MIN_VIRT_IRQ + 1)
+
+unsigned int virt_irq_max;
+static unsigned int max_virt_irq;
+static unsigned int nr_virt_irqs;
 
 void
 virt_irq_init(void)
 {
         int i;
+
+        if ((virt_irq_max == 0) || (virt_irq_max > (NR_IRQS - 1)))
+                virt_irq_max = NR_IRQS - 1;
+        max_virt_irq = virt_irq_max - __irq_offset_value;
+        nr_virt_irqs = max_virt_irq - MIN_VIRT_IRQ + 1;
+
         for (i = 0; i < NR_IRQS; i++)
                 virt_irq_to_real_map[i] = UNDEFINED_IRQ;
 }
@@ -308,17 +316,17 @@ int virt_irq_create_mapping(unsigned int real_irq)
                 return real_irq;
         }
 
-        /* map to a number between MIN_VIRT_IRQ and MAX_VIRT_IRQ */
+        /* map to a number between MIN_VIRT_IRQ and max_virt_irq */
         virq = real_irq;
-        if (virq > MAX_VIRT_IRQ)
-                virq = (virq % NR_VIRT_IRQS) + MIN_VIRT_IRQ;
+        if (virq > max_virt_irq)
+                virq = (virq % nr_virt_irqs) + MIN_VIRT_IRQ;
 
         /* search for this number or a free slot */
         first_virq = virq;
         while (virt_irq_to_real_map[virq] != UNDEFINED_IRQ) {
                 if (virt_irq_to_real_map[virq] == real_irq)
                         return virq;
-                if (++virq > MAX_VIRT_IRQ)
+                if (++virq > max_virt_irq)
                         virq = MIN_VIRT_IRQ;
                 if (virq == first_virq)
                         goto nospace;   /* oops, no free slots */
@@ -330,8 +338,8 @@ int virt_irq_create_mapping(unsigned int real_irq)
  nospace:
         if (!warned) {
                 printk(KERN_CRIT "Interrupt table is full\n");
-                printk(KERN_CRIT "Increase NR_IRQS (currently %d) "
-                       "in your kernel sources and rebuild.\n", NR_IRQS);
+                printk(KERN_CRIT "Increase virt_irq_max (currently %d) "
+                       "in your kernel sources and rebuild.\n", virt_irq_max);
                 warned = 1;
         }
         return NO_IRQ;
@@ -349,8 +357,8 @@ unsigned int real_irq_to_virt_slowpath(unsigned int real_irq)
 
         virq = real_irq;
 
-        if (virq > MAX_VIRT_IRQ)
-                virq = (virq % NR_VIRT_IRQS) + MIN_VIRT_IRQ;
+        if (virq > max_virt_irq)
+                virq = (virq % nr_virt_irqs) + MIN_VIRT_IRQ;
 
         first_virq = virq;
 
@@ -360,7 +368,7 @@ unsigned int real_irq_to_virt_slowpath(unsigned int real_irq)
 
                 virq++;
 
-                if (virq >= MAX_VIRT_IRQ)
+                if (virq >= max_virt_irq)
                         virq = 0;
 
         } while (first_virq != virq);