simplified RISC-V interrupt and clocksource handling v2

From: Christoph Hellwig
Date: Thu Aug 02 2018 - 12:03:47 EST


This series tries adds support for interrupt handling and timers
for the RISC-V architecture.

The basic per-hart interrupt handling implemented by the scause
and sie CSRs is extremely simple and implemented directly in
arch/riscv/kernel/irq.c. In addition there is a irqchip driver
for the PLIC external interrupt controller, which is called through
the set_handle_irq API, and a clocksource driver that gets its
timer interrupt directly from the low-level interrupt handling.

Compared to previous iterations this version does not try to use an
irqchip driver for the low-level interrupt handling. This saves
a couple indirect calls and an additional read of the scause CSR
in the hot path, makes the code much simpler and last but not least
avoid the dependency on a device tree for a mandatory architectural
feature.

A git tree is available here (contains a few more patches before
the ones in this series)

git://git.infradead.org/users/hch/riscv.git riscv-irq-simple.2

Gitweb:

http://git.infradead.org/users/hch/riscv.git/shortlog/refs/heads/riscv-irq-simple.2

Changes since v1:
- rename the plic driver to irq-sifive-plic
- switch to a default compatible of sifive,plic0 (still supporting the
riscv,plic0 name for compatibility)
- add a reference for the SiFive PLIC register layout
- fix plic_toggle addressing for large numbers of hwirqs
- remove the call to ack_bad_irq
- use a raw spinlock for plic_toggle_lock
- use the irq_desc cpumask in the plic enable/disable methods
- add back OF contexid parsing in the plic driver
- don't allow COMPILE_TEST builds of the clocksource driver, as it
depends on <asm/sbi.h>
- default the clocksource driver to y
- clean up naming in the clocksource driver
- remove the MINDELTA and MAXDELTA #defines
- various DT binding fixes