[Xen-devel] [PATCH 2/2] xen: arm: Warn if timer interrupts are not level triggered

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

Edge trigger arch timer interrupts really don't make much sense, so if
we discover we are booting on such a system issue a warning.

So far this has only been seen on the fast model emulators which have
both an incorrect DT description of the interrupt and a writeable
ICFGR allowing us to program the incorrect configuration. Other
platforms have incorrect DT descriptions (warned about by previous
patch) but the corresponding ICFGR isn't actually writeable so the
eventual configuration is level as desired.

I did consider overriding the incorrect DT on such systems but since
so far it has only been observed on emulators and we have code in
place to deal with edge triggering here I think warning is sufficient
for now.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 xen/arch/arm/time.c |   30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/xen/arch/arm/time.c b/xen/arch/arm/time.c
index 418748d..7304cd8 100644
--- a/xen/arch/arm/time.c
+++ b/xen/arch/arm/time.c
@@ -198,6 +198,32 @@ static void vtimer_interrupt(int irq, void *dev_id, struct 
cpu_user_regs *regs)
     vgic_vcpu_inject_irq(current, current->arch.virt_timer.irq);
 }
 
+/*
+ * Arch timer interrupt really ought to be level triggered, since the
+ * design of the timer/comparator mechanism is based around that
+ * concept.
+ *
+ * However some firmware (incorrectly) describes the interrupts as
+ * edge triggered and, worse, some hardware allows us to program the
+ * interrupt contoller as edge triggered.
+ *
+ * Check each interrupt and warn if we find ourselves in this situation.
+ */
+static void check_timer_irq_cfg(unsigned int irq, const char *which)
+{
+    struct irq_desc *desc = irq_to_desc(irq);
+
+    /*
+     * The interrupt contoller driver will update desc->arch.type with
+     * the actual type which ended up configured in the hardware.
+     */
+    if ( desc->arch.type & DT_IRQ_TYPE_LEVEL_LOW )
+        return;
+
+    printk(XENLOG_WARNING
+           "WARNING: %s-timer IRQ%u is not level triggered.\n", which, irq);
+}
+
 /* Set up the timer interrupt on this CPU */
 void __cpuinit init_timer_interrupt(void)
 {
@@ -215,6 +241,10 @@ void __cpuinit init_timer_interrupt(void)
                    "virtimer", NULL);
     request_irq(timer_irq[TIMER_PHYS_NONSECURE_PPI], 0, timer_interrupt,
                 "phytimer", NULL);
+
+    check_timer_irq_cfg(timer_irq[TIMER_HYP_PPI], "hypervisor");
+    check_timer_irq_cfg(timer_irq[TIMER_VIRT_PPI], "virtual");
+    check_timer_irq_cfg(timer_irq[TIMER_PHYS_NONSECURE_PPI], "NS-physical");
 }
 
 /* Wait a set number of microseconds */
-- 
1.7.10.4


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