RFC: simplified RISC-V interrupt and clocksource handling

From: Christoph Hellwig <hch@lst.de>
To: tglx@linutronix.de, palmer@sifive.com, jason@lakedaemon.net,
	marc.zyngier@arm.com, robh+dt@kernel.org, mark.rutland@arm.com
Cc: anup@brainfault.org, atish.patra@wdc.com,
	devicetree@vger.kernel.org, aou@eecs.berkeley.edu,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	shorne@gmail.com
Subject: RFC: simplified RISC-V interrupt and clocksource handling
Date: Thu, 26 Jul 2018 16:37:14 +0200	[thread overview]
Message-ID: <20180726143723.16585-1-hch@lst.de> (raw)

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

Gitweb:

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