Patch "irqchip/omap-intc: Add support for spurious irq handling" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

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

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     irqchip-omap-intc-add-support-for-spurious-irq-handling.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From d3b421cd07e4c0d4d6c0bbd55ca169c054fc081d Mon Sep 17 00:00:00 2001
From: Sekhar Nori <nsekhar@ti.com>
Date: Tue, 15 Dec 2015 19:56:12 +0530
Subject: irqchip/omap-intc: Add support for spurious irq handling

From: Sekhar Nori <nsekhar@ti.com>

commit d3b421cd07e4c0d4d6c0bbd55ca169c054fc081d upstream.

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
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/irqchip/irq-omap-intc.c |   27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

--- 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
 
@@ -330,11 +331,35 @@ static int __init omap_init_irq(u32 base
 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);
 }
 


Patches currently in stable-queue which might be from nsekhar@ti.com are

queue-4.4/irqchip-omap-intc-add-support-for-spurious-irq-handling.patch