linux-kernel - Re: RFC: simplified RISC-V interrupt and clocksource handling

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Message-ID: <20180727144405.GB29626@lst.de>
Date:   Fri, 27 Jul 2018 16:44:05 +0200
From:   Christoph Hellwig <hch@....de>
To:     Atish Patra <atish.patra@....com>
Cc:     Christoph Hellwig <hch@....de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "palmer@...ive.com" <palmer@...ive.com>,
        "jason@...edaemon.net" <jason@...edaemon.net>,
        "marc.zyngier@....com" <marc.zyngier@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "anup@...infault.org" <anup@...infault.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "shorne@...il.com" <shorne@...il.com>
Subject: Re: RFC: simplified RISC-V interrupt and clocksource handling

On Thu, Jul 26, 2018 at 04:38:43PM -0700, Atish Patra wrote:
> 1. As per my understanding, timer interrupt now can't be registered as a 
> Linux IRQ now. Thus, /proc/interrupts will not be automatically populated 
> for timer interrupt stats. Am I wrong in my assumption?

Yes, with this code the timer interrupt does not show up in
/proc/interrupts.  I wonder if that is an issue and if there is any
precedence for it?

> 2. The future version of local interrupt controller known as Core Level 
> Interrupt Controller aka CLIC. Do we have to change the current design
> again for CLIC in future?
>
> Here are the docs:
> https://github.com/sifive/clic-spec/blob/master/clic.adoc

This doesn't really look like 'the future' version but a proposal for
something more like low end realtime microcontrollers ala ARM Cortex M*.
At least the priorities don't really make much sense for a general
purpose SOC.

Either way the existing architectural scause/sie interrupt handling will
remain but can be opted out, but if we really want to support the CLIC
it would have to grow a new irqchip driver, and the PLIC driver would
require a few dozend new lines of glue code to chain underneath it.