linux-kernel - Re: [v5 PATCH] RISC-V: Fix unsupported isa string info.

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Date:   Fri, 13 Sep 2019 13:47:25 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     Atish Patra <Atish.Patra@....com>,
        Christoph Hellwig <hch@...radead.org>, anup@...infault.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        aou@...s.berkeley.edu, johan@...nel.org
Subject:     Re: [v5 PATCH] RISC-V: Fix unsupported isa string info.

On Mon, 09 Sep 2019 23:00:10 PDT (-0700), Christoph Hellwig wrote:
> On Fri, Sep 06, 2019 at 11:27:57PM +0000, Atish Patra wrote:
>> > Agreed. May be something like this ?
>> >
>> > Let's say f/d is enabled in kernel but cpu doesn't support it.
>> > "unsupported isa" will only appear if there are any unsupported isa.
>> >
>> > processor       : 3
>> > hart            : 4
>> > isa             : rv64imac
>> > unsupported isa	: fd
>> > mmu             : sv39
>> > uarch           : sifive,u54-mc
>> >
>> > May be I am just trying over optimize one corner case :) :).
>> > /proc/cpuinfo should just print all the isa string. That's it.
>> >
>>
>> Ping ?
>
> Yes, I agree with the "dumb" reporting of all capabilities.

I agree: it looks like other architectures are passing info (ie, x86 flags) 
that isn't supported by userspace.  We have the ELF hwcap stuff for those who 
want to tell which instructions they can run, so it's sane to just keep this 
simple.