C-SKY CPU Architecture Port Updated For Linux 4.21

Back during the Linux 4.20 kernel cycle, support for the C-SKY CPU architecture was introduced while now for Linux 4.21 it has seen its first round of improvements.

C-SKY is a 32-bit CPU architecture out of China intended for embedded devices from DVRs to printers to media boxes and other low-power consumer electronics. C-SKY Microsystems has joined the RISC-V Foundation, but this architecture added to Linux 4.21 is not RISC-V based but their own home-grown design with support for 16/32-bit variable length instructions, 70+ core instructions, and is a two-stage pipeline processor.

With the in-development Linux 4.21 kernel, the C-SKY code is picking up CPU hotplug support for SMP, ftrace, perf subsystem support, optimizations, and a wide range of fixes.

The C-SKY updates for Linux 4.21 have more than fifteen hundred lines of new code and the complete list of changes can be found via this pull request.