xen/arm: introduce GIC_PRI_TO_GUEST macro

GICH_LR registers and GICH_VMCR only support 5 bits for guest irq
priorities.
Introduce a macro to reduce the 8-bit priority fields to 5 bits; use it
in gic.c.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

xen/arch/arm/gic.c

@@ -561,7 +561,7 @@ static inline void gic_set_lr(int lr, struct pending_irq *p,
     BUG_ON(lr < 0);
     BUG_ON(state & ~(GICH_LR_STATE_MASK<<GICH_LR_STATE_SHIFT));
 
-    lr_val = state | ((p->priority >> 3) << GICH_LR_PRIORITY_SHIFT) |
+    lr_val = state | (GIC_PRI_TO_GUEST(p->priority) << GICH_LR_PRIORITY_SHIFT) |
         ((p->irq & GICH_LR_VIRTUAL_MASK) << GICH_LR_VIRTUAL_SHIFT);
     if ( p->desc != NULL )
         lr_val |= GICH_LR_HW | (p->desc->irq << GICH_LR_PHYSICAL_SHIFT);

xen/include/asm-arm/gic.h

@@ -149,6 +149,8 @@
 #define GIC_PRI_IRQ        0xa0
 #define GIC_PRI_IPI        0x90 /* IPIs must preempt normal interrupts */
 #define GIC_PRI_HIGHEST    0x80 /* Higher priorities belong to Secure-World */
+#define GIC_PRI_TO_GUEST(pri) (pri >> 3) /* GICH_LR and GICH_VMCR only support
+                                            5 bits for guest irq priority */
 
 
 #ifndef __ASSEMBLY__