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

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Message-ID: <mhng-6c980844-cfea-4aaa-ac86-3c99ce6a6d14@palmer-si-x1e>
Date:   Tue, 27 Aug 2019 16:37:16 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     Christoph Hellwig <hch@....de>
CC:     mark.rutland@....com, Christoph Hellwig <hch@....de>,
        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 Mon, 19 Aug 2019 03:16:48 PDT (-0700), Christoph Hellwig wrote:
> On Tue, Aug 13, 2019 at 05:29:58PM +0100, Mark Rutland wrote:
>> > +	np = of_find_compatible_node(NULL, NULL, "riscv,clint0");
>>
>> Since the MMIO layout is that of the SiFive clint, the compatible string
>> should be specific to that. e.g. "sifive,clint". That way it will be
>> possible to distinguish it from other implementations.
>>
>> What exactly is the "0" suffix for? Is that a version number?
>>
>> If that's a CPU index, then I don't think that's the right way to encode
>> this unless the programming interface actually differs across CPUs. It
>> would be better to use an explicit phandle to express the affinity.
>
> It isn't a cpu index, I suspect a version number.  These show up
> in a lot of the early RISC-V DTs coming from the UCB/SiFive sphere.
> They've now spread everywhere unfortunately.

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.