genirq: Allow irq chips to mark themself oneshot safe

Some interrupt chips like MSI are oneshot safe by implementation. For
those interrupts we can avoid the mask/unmask sequence for threaded
interrupt handlers.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1207132056540.32033@ionos
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Jan Kiszka <jan.kiszka@web.de>

2 files changed, 15 insertions, 1 deletions

diff --git a/include/linux/irq.h b/include/linux/irq.h
index 553fb66da130..216b0ba109d7 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -349,6 +349,7 @@ enum {
         IRQCHIP_MASK_ON_SUSPEND         = (1 <<  2),
         IRQCHIP_ONOFFLINE_ENABLED       = (1 <<  3),
         IRQCHIP_SKIP_SET_WAKE           = (1 <<  4),
+        IRQCHIP_ONESHOT_SAFE            = (1 <<  5),
 };
 
 /* This include will go away once we isolated irq_desc usage to core code */
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 8c548232ba39..2e326d1ebec1 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -960,6 +960,18 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
         }
 
         /*
+         * Drivers are often written to work w/o knowledge about the
+         * underlying irq chip implementation, so a request for a
+         * threaded irq without a primary hard irq context handler
+         * requires the ONESHOT flag to be set. Some irq chips like
+         * MSI based interrupts are per se one shot safe. Check the
+         * chip flags, so we can avoid the unmask dance at the end of
+         * the threaded handler for those.
+         */
+        if (desc->irq_data.chip->flags & IRQCHIP_ONESHOT_SAFE)
+                new->flags &= ~IRQF_ONESHOT;
+
+        /*
          * The following block of code has to be executed atomically
          */
         raw_spin_lock_irqsave(&desc->lock, flags);
@@ -1033,7 +1045,8 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
                  */
                 new->thread_mask = 1 << ffz(thread_mask);
 
-        } else if (new->handler == irq_default_primary_handler) {
+        } else if (new->handler == irq_default_primary_handler &&
+                   !(desc->irq_data.chip->flags & IRQCHIP_ONESHOT_SAFE)) {
                 /*
                  * The interrupt was requested with handler = NULL, so
                  * we use the default primary handler for it. But it