ppc+riscv/irq: introduce a dummy irq_to_desc()

In preparation for irq_to_desc() being called by common IRQ code.
PowerPC doesn't have an irq_desc array defined, so it cannot use the
generic irq_to_desc macro in the common header.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
master commit: ed39935f50
master date: 2026-06-29 17:14:47 +0200

xen/arch/ppc/include/asm/irq.h

@@ -30,4 +30,10 @@ static inline int platform_get_irq(const struct dt_device_node *device, int inde
     BUG_ON("unimplemented");
 }
 
+static inline void *irq_to_desc(unsigned int irq)
+{
+    BUG_ON("unimplemented");
+}
+#define irq_to_desc irq_to_desc
+
 #endif /* __ASM_PPC_IRQ_H__ */

xen/arch/riscv/include/asm/irq.h

@@ -25,6 +25,12 @@ static inline void arch_move_irqs(struct vcpu *v)
     BUG_ON("unimplemented");
 }
 
+static inline void *irq_to_desc(unsigned int irq)
+{
+    BUG_ON("unimplemented");
+}
+#define irq_to_desc irq_to_desc
+
 #endif /* ASM__RISCV__IRQ_H */
 
 /*