linux-kernel - RE: [PATCH 3/4] RISC-V: Support case insensitive ISA string parsing.

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Date:   Sat, 27 Jul 2019 00:52:59 -0700 (PDT)
From:   Paul Walmsley <paul.walmsley@...ive.com>
To:     Anup Patel <Anup.Patel@....com>
cc:     Atish Patra <Atish.Patra@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alan Kao <alankao@...estech.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Allison Randal <allison@...utok.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johan Hovold <johan@...nel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: RE: [PATCH 3/4] RISC-V: Support case insensitive ISA string
 parsing.

On Sat, 27 Jul 2019, Anup Patel wrote:

> > -----Original Message-----
> > From: Paul Walmsley <paul.walmsley@...ive.com>
> > Sent: Saturday, July 27, 2019 5:00 AM
> > 
> > On Fri, 26 Jul 2019, Atish Patra wrote:
> > 
> > > On 7/26/19 1:47 PM, Paul Walmsley wrote:
> > > > On Fri, 26 Jul 2019, Atish Patra wrote:
> > > >
> > > > > As per riscv specification, ISA naming strings are case
> > > > > insensitive. However, currently only lower case strings are parsed
> > > > > during cpu procfs.
> > > > >
> > > > > Support parsing of upper case letters as well.
> > > > >
> > > > > Signed-off-by: Atish Patra <atish.patra@....com>
> > > >
> > > > Is there a use case that's driving this, or
> > >
> > > Currently, we use all lower case isa string in kvmtool. But somebody
> > > can have uppercase letters in future as spec allows it.
> > >
> > >
> > > can we just say, "use
> > > > lowercase letters" and leave it at that?
> > > >
> > >
> > > In that case, it will not comply with RISC-V spec. Is that okay ?
> > 
> > I think that section of the specification is mostly concerned with someone
> > trying to define "f" as a different extension than "F", or something like that.
> > I'm not sure that it imposes any constraint that software must accept both
> > upper and lower case ISA strings.
> > 
> > What gives me pause here is that this winds up impacting DT schema
> > validation:
> > 
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Docu
> > mentation/devicetree/bindings/riscv/cpus.yaml#n41
> 
> If 'f' and 'F' mean same extension as-per RISC-V spec then software should also
> interpret it that way hence this patch.

The list of valid RISC-V ISA strings is already constrained by the DT 
schema to be all lowercase.  Anything else would violate the schema.

I'd take a patch that would pr_warn() or a BUG() if any uppercase letters 
were found in the riscv,isa DT property, though, in case the developer 
skipped the DT schema validator.


- Paul