linux-kernel - Re: [PATCH 08/15] riscv: provide native clint access for M-mode

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Date:   Wed, 4 Sep 2019 10:05:39 +0800
From:   Alan Kao <alankao@...estech.com>
To:     Palmer Dabbelt <palmer@...ive.com>
CC:     Christoph Hellwig <hch@....de>, <mark.rutland@....com>,
        Damien Le Moal <Damien.LeMoal@....com>,
        <linux-kernel@...r.kernel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH 08/15] riscv: provide native clint access for M-mode

On Tue, Sep 03, 2019 at 11:48:52AM -0700, Palmer Dabbelt wrote:
> On Tue, 27 Aug 2019 23:11:46 PDT (-0700), Christoph Hellwig wrote:
> >On Tue, Aug 27, 2019 at 04:37:16PM -0700, Palmer Dabbelt wrote:
> >>clint0 would be version 0 of the clint, with is the core-local interrupt
> >>controller in rocket chip.  It should be "sifive,clint-1.0.0", not
> >>"riscv,clint0", as it's a SiFive widget.  Unfortunately there are a lot of
> >>legacy device trees floating around, but I'm only considering what's been
> >>upstream to be actually part of the spec.
> >>
> >>In this case the code should match on a "sifive,clint-1.0.0", and the
> >>device trees should be fixed up to match.  We match on "riscv,plic0" for
> >>legacy systems, and I guess it makes sense to do something similar here.
> >
> >IFF we decided to change it I'd rather separate DT noes for the ipi
> >bank vs timecmp register vs timeval to support variable layouts.  The
> >downside is that we can't just boot on unmodified upstream qemu, which
> >has used the "riscv,clint0" for years.
> 
> Like I alluded to above, matching on "riscv,clint0" seems reasonable to me
> as it's a defacto standard -- we'll just have to make sure that if we ever
> end up with a RISC-V CLINT that the DT entry is something else.

De facto, but not mandatory.

> 
> As far as splitting the memory maps goes, I don't have a strong opinion but
> it seems like that'll introduce more complexity than it's worth.
> 

At least the splitting can keep reminding us and any new comers in the future
that CLINT is not (yet) a must in RISC-V landscape.  A previous discussion
FYI: ( https://lkml.org/lkml/2019/8/20/1361 )

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