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

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Date:   Tue, 03 Sep 2019 11:48:52 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     Christoph Hellwig <hch@....de>
CC:     Christoph Hellwig <hch@....de>, mark.rutland@....com,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Damien Le Moal <Damien.LeMoal@....com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject:     Re: [PATCH 08/15] riscv: provide native clint access for M-mode

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.

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.