+ * Different ways of handling interrupts. Tile interrupts are always
+ * per-cpu; there is no global interrupt controller to implement
+ * enable/disable. Most onboard devices can send their interrupts to
+ * many tiles at the same time, and Tile-specific drivers know how to
+ * deal with this.
+ *
+ * However, generic devices (usually PCIE based, sometimes GPIO)
+ * expect that interrupts will fire on a single core at a time and
+ * that the irq can be enabled or disabled from any core at any time.
+ * We implement this by directing such interrupts to a single core.
+ *
+ * One added wrinkle is that PCI interrupts can be either
+ * hardware-cleared (legacy interrupts) or software cleared (MSI).
+ * Other generic device systems (GPIO) are always software-cleared.
+ *
+ * The enums below are used by drivers for onboard devices, including
+ * the internals of PCI root complex and GPIO. They allow the driver
+ * to tell the generic irq code what kind of interrupt is mapped to a
+ * particular IRQ number.
+ */
+enum {
+ /* per-cpu interrupt; use enable/disable_percpu_irq() to mask */
+ TILE_IRQ_PERCPU,
+ /* global interrupt, hardware responsible for clearing. */
+ TILE_IRQ_HW_CLEAR,
+ /* global interrupt, software responsible for clearing. */
+ TILE_IRQ_SW_CLEAR,
+};
+
+
+/*
+ * Paravirtualized drivers should call this when they dynamically
+ * allocate a new IRQ or discover an IRQ that was pre-allocated by the
+ * hypervisor for use with their particular device. This gives the
+ * IRQ subsystem an opportunity to do interrupt-type-specific
+ * initialization.
+ *
+ * ISSUE: We should modify this API so that registering anything
+ * except percpu interrupts also requires providing callback methods
+ * for enabling and disabling the interrupt. This would allow the
+ * generic IRQ code to proxy enable/disable_irq() calls back into the
+ * PCI subsystem, which in turn could enable or disable the interrupt
+ * at the PCI shim.