irqchip/irq-pruss-intc: Add a PRUSS irqchip driver for PRUSS interrupts

irqchip/irq-pruss-intc: Add a PRUSS irqchip driver for PRUSS interrupts

The Programmable Real-Time Unit Subsystem (PRUSS) contains a local
interrupt controller (INTC) that can handle various system input events
and post interrupts back to the device-level initiators. The INTC can
support upto 64 input events with individual control configuration and
hardware prioritization. These events are mapped onto 10 output interrupt
lines through two levels of many-to-one mapping support. Different
interrupt lines are routed to the individual PRU cores or to the host
CPU, or to other devices on the SoC. Some of these events are sourced
from peripherals or other sub-modules within that PRUSS, while a few
others are sourced from SoC-level peripherals/devices.

The PRUSS INTC platform driver manages this PRUSS interrupt controller
and implements an irqchip driver to provide a Linux standard way for
the PRU client users to enable/disable/ack/re-trigger a PRUSS system
event. The system events to interrupt channels and output interrupts
relies on the mapping configuration provided either through the PRU
firmware blob (for interrupts routed to PRU cores) or via the PRU
application's device tree node (for interrupt routed to the main CPU).
In the first case the mappings will be programmed on PRU remoteproc
driver demand (via irq_create_fwspec_mapping) during the boot of a PRU
core and cleaned up after the PRU core is stopped.

Reference counting is used to allow multiple system events to share a
single channel and to allow multiple channels to share a single host
event.

The PRUSS INTC module is reference counted during the interrupt
setup phase through the irqchip's irq_request_resources() and
irq_release_resources() ops. This restricts the module from being
removed as long as there are active interrupt users.

The driver currently supports and can be built for OMAP architecture
based AM335x, AM437x and AM57xx SoCs; Keystone2 architecture based
66AK2G SoCs and Davinci architecture based OMAP-L13x/AM18x/DA850 SoCs.
All of these SoCs support 64 system events, 10 interrupt channels and
10 output interrupt lines per PRUSS INTC with a few SoC integration
differences.

NOTE:
Each PRU-ICSS's INTC on AM57xx SoCs is preceded by a Crossbar that
enables multiple external events to be routed to a specific number
of input interrupt events. Any non-default external interrupt event
directed towards PRUSS needs this crossbar to be setup properly.

Co-developed-by: Suman Anna <s-anna@ti.com>
Co-developed-by: Andrew F. Davis <afd@ti.com>
Co-developed-by: Roger Quadros <rogerq@ti.com>
Co-developed-by: David Lechner <david@lechnology.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Grzegorz Jaszczyk <grzegorz.jaszczyk@linaro.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>