irqchip/omap-intc: Add support for spurious irq handling

Under some conditions, irq sorting procedure used by INTC can go wrong
resulting in a spurious irq getting reported.

If this condition is not handled, it results in endless stream of:

    unexpected IRQ trap at vector 00

messages from ack_bad_irq()

Handle the spurious interrupt condition in omap-intc driver to prevent this.

Measurements using kernel function profiler on AM335x EVM running at 720MHz
show that after this patch omap_intc_handle_irq() takes about 37.4us against
34us before this patch.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Felipe Balbi <balbi@ti.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Link: http://lkml.kernel.org/r/9c78a6db02ac55f7af7371b417b6e414d2c3095b.1450188128.git.nsekhar@ti.com
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 26 insertions, 1 deletions

diff --git a/drivers/irqchip/irq-omap-intc.c b/drivers/irqchip/irq-omap-intc.c
index ed25175ae9fa..9d1bcfc33e4c 100644
--- a/drivers/irqchip/irq-omap-intc.c
+++ b/drivers/irqchip/irq-omap-intc.c
@@ -47,6 +47,7 @@
 #define INTC_ILR0               0x0100
 
 #define ACTIVEIRQ_MASK          0x7f    /* omap2/3 active interrupt bits */
+#define SPURIOUSIRQ_MASK        (0x1ffffff << 7)
 #define INTCPS_NR_ILR_REGS      128
 #define INTCPS_NR_MIR_REGS      4
 
@@ -329,11 +330,35 @@ static int __init omap_init_irq(u32 base, struct device_node *node)
 static asmlinkage void __exception_irq_entry
 omap_intc_handle_irq(struct pt_regs *regs)
 {
+        extern unsigned long irq_err_count;
         u32 irqnr;
 
         irqnr = intc_readl(INTC_SIR);
+
+        /*
+         * A spurious IRQ can result if interrupt that triggered the
+         * sorting is no longer active during the sorting (10 INTC
+         * functional clock cycles after interrupt assertion). Or a
+         * change in interrupt mask affected the result during sorting
+         * time. There is no special handling required except ignoring
+         * the SIR register value just read and retrying.
+         * See section 6.2.5 of AM335x TRM Literature Number: SPRUH73K
+         *
+         * Many a times, a spurious interrupt situation has been fixed
+         * by adding a flush for the posted write acking the IRQ in
+         * the device driver. Typically, this is going be the device
+         * driver whose interrupt was handled just before the spurious
+         * IRQ occurred. Pay attention to those device drivers if you
+         * run into hitting the spurious IRQ condition below.
+         */
+        if (unlikely((irqnr & SPURIOUSIRQ_MASK) == SPURIOUSIRQ_MASK)) {
+                pr_err_once("%s: spurious irq!\n", __func__);
+                irq_err_count++;
+                omap_ack_irq(NULL);
+                return;
+        }
+
         irqnr &= ACTIVEIRQ_MASK;
-        WARN_ONCE(!irqnr, "Spurious IRQ ?\n");
         handle_domain_irq(domain, irqnr, regs);
 }