linux-phytec-ti

remoteproc/pruss: add PRU remoteproc driver

The Programmable Real-Time Unit Subsystem (PRUSS) consists of
dual 32-bit RISC cores (Programmable Real-Time Units, or PRUs)
for program execution. This patch adds a remoteproc platform
driver for managing the individual PRU RISC cores life cycle.

The PRU platform driver allows to provide specific device data
like PRU Id, firmware name etc using SoC-specific match data and
appropriate compatible strings. The PRU remoteproc driver uses
the standard remoteproc core ELF loader. However, the PRUs do not
have a unified address space, (has an Instruction RAM and a primary
Data RAM at both 0x0) and leverage an added .da_to_va ops to use
the standard ELF loader. This remoteproc driver does not have
support for error recovery and system suspend/resume features.

The PRU interrupt configuration is handled within the PRUSS INTC
platform driver, and leverages the system events to interrupt
channels and host interrupts mapping configuration through a
PRU firmware resource table for now. This will be revisited and
enhanced in the future for a better interface. The mappings
are currently programmed during the booting/shutdown of the PRU.

The PRU remoteproc driver is also designed to support virtio-ring
based communication between MPU and a PRU core on supported
firmwares. The virtio-ring signalling support is provided either
through a OMAP mailbox or through two PRU system events - one event
used in each direction for kicking from one processor and receiving
notification on the other processor. The driver supports both
signalling options, and they are designed to be used in mutually
exclusive fashion. The mailbox-based signalling takes precedence
if both options are mentioned. Either of the options would require
the corresponding firmware support though.

The driver currently supports the AM335x SoC, and support for other
TI SoCs will be added in subsequent patches. The PRU remoteproc
driver expects the firmware names to be the following for each of
the PRU cores: "am335x-pru0-fw" and "am335x-pru1-fw". The driver
leverages the 'auto-boot' feature from remoteproc core, and the
firmware names can be adjusted if required through the sysfs
interface provided by the remoteproc core.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>