[PATCH v3 1/2] clocksource/arm_arch_timer: Force per-CPU interrupt to be level-triggered

Marc Zyngier marc.zyngier at arm.com
Mon Jun 6 10:56:30 PDT 2016

The ARM architected timer produces level-triggered interrupts (this
is mandated by the architecture). Unfortunately, most device-trees
get this wrong, and expose an edge-triggered interrupt.

Until now, this wasn't too much an issue, as the programming of the
trigger would fail (the corresponding PPI cannot be reconfigured),
and the kernel would be happy with this. But we're about to change
this, and trust DT a lot if the driver doesn't provide its own
trigger information. In that context, the timer breaks badly.

While we do need to fix the DTs, there is also some userspace out
there (kvmtool) that generates the same kind of broken DT on the
fly, and that will completely break with newer kernels.

As a safety measure, and to keep buggy software alive as well as
buying us some time to fix DTs all over the place, let's check
what trigger configuration has been given us by the firmware.
If this is not a level configuration, then we know that the
DT/ACPI configuration is bust, and we pick some defaults which
won't be worse than the existing setup.

Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
 drivers/clocksource/arm_arch_timer.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 3628ac8..1310641 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -8,6 +8,9 @@
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
+#define pr_fmt(fmt)	"arm_arch_timer: " fmt
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/device.h>
@@ -462,14 +465,32 @@ static bool arch_timer_has_nonsecure_ppi(void)
+static u32 check_ppi_trigger(int irq)
+	u32 flags = irq_get_trigger_type(irq);
+	if (flags != IRQF_TRIGGER_HIGH && flags != IRQF_TRIGGER_LOW) {
+		pr_warn("WARNING: Invalid trigger for IRQ%d, assuming level low\n", irq);
+		pr_warn("WARNING: Please fix your firmware\n");
+		flags = IRQF_TRIGGER_LOW;
+	}
+	return flags;
 static int arch_timer_setup(struct clock_event_device *clk)
+	u32 flags;
 	__arch_timer_setup(ARCH_CP15_TIMER, clk);
-	enable_percpu_irq(arch_timer_ppi[arch_timer_uses_ppi], 0);
+	flags = check_ppi_trigger(arch_timer_ppi[arch_timer_uses_ppi]);
+	enable_percpu_irq(arch_timer_ppi[arch_timer_uses_ppi], flags);
-	if (arch_timer_has_nonsecure_ppi())
-		enable_percpu_irq(arch_timer_ppi[PHYS_NONSECURE_PPI], 0);
+	if (arch_timer_has_nonsecure_ppi()) {
+		flags = check_ppi_trigger(arch_timer_ppi[PHYS_NONSECURE_PPI]);
+		enable_percpu_irq(arch_timer_ppi[PHYS_NONSECURE_PPI], flags);
+	}

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