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-rw-r--r--include/hw/arm/armv7m.h4
-rw-r--r--include/hw/irq.h18
2 files changed, 21 insertions, 1 deletions
diff --git a/include/hw/arm/armv7m.h b/include/hw/arm/armv7m.h
index d2c74d3872..a30e3c6471 100644
--- a/include/hw/arm/armv7m.h
+++ b/include/hw/arm/armv7m.h
@@ -35,7 +35,9 @@ typedef struct {
 
 /* ARMv7M container object.
  * + Unnamed GPIO input lines: external IRQ lines for the NVIC
- * + Named GPIO output SYSRESETREQ: signalled for guest AIRCR.SYSRESETREQ
+ * + Named GPIO output SYSRESETREQ: signalled for guest AIRCR.SYSRESETREQ.
+ *   If this GPIO is not wired up then the NVIC will default to performing
+ *   a qemu_system_reset_request(SHUTDOWN_CAUSE_GUEST_RESET).
  * + Property "cpu-type": CPU type to instantiate
  * + Property "num-irq": number of external IRQ lines
  * + Property "memory": MemoryRegion defining the physical address space
diff --git a/include/hw/irq.h b/include/hw/irq.h
index 24ba0ece11..dc7abf199e 100644
--- a/include/hw/irq.h
+++ b/include/hw/irq.h
@@ -55,4 +55,22 @@ qemu_irq qemu_irq_split(qemu_irq irq1, qemu_irq irq2);
    on an existing vector of qemu_irq.  */
 void qemu_irq_intercept_in(qemu_irq *gpio_in, qemu_irq_handler handler, int n);
 
+/**
+ * qemu_irq_is_connected: Return true if IRQ line is wired up
+ *
+ * If a qemu_irq has a device on the other (receiving) end of it,
+ * return true; otherwise return false.
+ *
+ * Usually device models don't need to care whether the machine model
+ * has wired up their outbound qemu_irq lines, because functions like
+ * qemu_set_irq() silently do nothing if there is nothing on the other
+ * end of the line. However occasionally a device model will want to
+ * provide default behaviour if its output is left floating, and
+ * it can use this function to identify when that is the case.
+ */
+static inline bool qemu_irq_is_connected(qemu_irq irq)
+{
+    return irq != NULL;
+}
+
 #endif