[qemu-xen staging] include/hw/irq.h: New function qemu_irq_is_connected()

[patchbot@xxxxxxx]

commit faf7c6de34fb8eaa566726cc658ba5ad81fb32af
Author:     Peter Maydell <peter.maydell@xxxxxxxxxx>
AuthorDate: Mon Aug 3 17:55:03 2020 +0100
Commit:     Peter Maydell <peter.maydell@xxxxxxxxxx>
CommitDate: Mon Aug 3 17:55:03 2020 +0100

    include/hw/irq.h: New function qemu_irq_is_connected()
    
    Mostly devices don't need to care whether one of their output
    qemu_irq lines is connected, because functions like qemu_set_irq()
    silently do nothing if there is nothing on the other end.  However
    sometimes a device might want to implement default behaviour for the
    case where the machine hasn't wired the line up to anywhere.
    
    Provide a function qemu_irq_is_connected() that devices can use for
    this purpose.  (The test is trivial but encapsulating it in a
    function makes it easier to see where we're doing it in case we need
    to change the implementation later.)
    
    Signed-off-by: Peter Maydell <peter.maydell@xxxxxxxxxx>
    Reviewed-by: Philippe Mathieu-Daudé <f4bug@xxxxxxxxx>
    Reviewed-by: Alistair Francis <alistair.francis@xxxxxxx>
    Message-id: 20200728103744.6909-2-peter.maydell@xxxxxxxxxx
---
 include/hw/irq.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

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
--
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