On Wed, Dec 3, 2014 at 8:18 AM, Marc Zyngier [off-list ref] wrote:

There is a number of cases where a kernel subsystem may want to
introspect the state of an interrupt at the irqchip level:

- When a peripheral is shared between virtual machines,
  its interrupt state becomes part of the guest's state,
  and must be switched accordingly. KVM on arm/arm64 requires
  this for its guest-visible timer
- Some GPIO controllers seem to require peeking into the
  interrupt controller they are connected to to report
  their internal state

This seem to be a pattern that is common enough for the core code
to try and support this without too many horrible hacks. Introduce
a pair of accessors (irq_get_irqchip_state/irq_set_irqchip_state)
to retrieve the bits that can be of interest to another subsystem:
pending, active, and masked.

- irq_get_irqchip_state returns the state of the interrupt according
  to a parameter set to IRQCHIP_STATE_PENDING, IRQCHIP_STATE_ACTIVE,
  IRQCHIP_STATE_MASKED or IRQCHIP_STATE_LINE_LEVEL.
- irq_set_irqchip_state similarly sets the state of the interrupt.

Signed-off-by: Marc Zyngier <redacted>

With the addition of actually assigning err to something useful in the
setter below:

Reviewed-by: Bjorn Andersson <redacted>
Tested-by: Bjorn Andersson <redacted>

[..]

+/**
+ *     irq_set_irqchip_state - set the state of a forwarded interrupt.
+ *     @irq: Interrupt line that is forwarded to a VM
+ *     @which: State to be restored (one of IRQCHIP_STATE_*)
+ *     @val: Value corresponding to @which
+ *
+ *     This call sets the internal irqchip state of an interrupt,
+ *     depending on the value of @which.
+ *
+ *     This function should be called with preemption disabled if the
+ *     interrupt controller has per-cpu registers.
+ */
+int irq_set_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
+                         bool val)
+{
+       struct irq_desc *desc;
+       struct irq_data *data;
+       struct irq_chip *chip;
+       unsigned long flags;
+       int err = -EINVAL;
+
+       desc = irq_get_desc_buslock(irq, &flags, 0);
+       if (!desc)
+               return err;
+
+       data = irq_desc_get_irq_data(desc);
+
+       do {
+               chip = irq_data_get_irq_chip(data);
+               if (chip->irq_set_irqchip_state)
+                       break;
+#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
+               data = data->parent_data;
+#else
+               data = NULL;
+#endif
+       } while (data);
+
+       if (data)
+               chip->irq_set_irqchip_state(data, which, val);

err =

+
+       irq_put_desc_busunlock(desc, flags);
+       return err;
+}

Regards,
Bjorn