ZEN: Add an option to make threadirqs the default

And a parameter 'nothreadirqs' to disable it again.

kernel/irq/Kconfig

@@ -111,6 +111,23 @@ config GENERIC_IRQ_RESERVATION_MODE
 config IRQ_FORCED_THREADING
        bool
 
+config FORCE_IRQ_THREADING
+	bool "Make IRQ threading compulsory"
+	depends on IRQ_FORCED_THREADING
+	default n
+	---help---
+
+	  Make IRQ threading mandatory for any IRQ handlers that support it
+	  instead of being optional and requiring the threadirqs kernel
+	  parameter. Instead they can be optionally disabled with the
+	  nothreadirqs kernel parameter.
+
+	  Enabling this may make some architectures not boot with runqueue
+	  sharing and MuQSS.
+
+	  Enable if you are building for a desktop or low latency system,
+	  otherwise say N.
+
 config SPARSE_IRQ
 	bool "Support sparse irq numbering" if MAY_HAVE_SPARSE_IRQ
 	---help---

kernel/irq/manage.c

@@ -24,9 +24,20 @@
 #include "internals.h"
 
 #if defined(CONFIG_IRQ_FORCED_THREADING) && !defined(CONFIG_PREEMPT_RT)
+#ifdef CONFIG_FORCE_IRQ_THREADING
+__read_mostly bool force_irqthreads = true;
+#else
 __read_mostly bool force_irqthreads;
+#endif
 EXPORT_SYMBOL_GPL(force_irqthreads);
 
+static int __init setup_noforced_irqthreads(char *arg)
+{
+	force_irqthreads = false;
+	return 0;
+}
+early_param("nothreadirqs", setup_noforced_irqthreads);
+
 static int __init setup_forced_irqthreads(char *arg)
 {
 	force_irqthreads = true;