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

From: Paul Walmsley <paul.walmsley@sifive.com>
To: Anup Patel <Anup.Patel@wdc.com>
Cc: Atish Patra <Atish.Patra@wdc.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Alan Kao <alankao@andestech.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Allison Randal <allison@lohutok.net>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Johan Hovold <johan@kernel.org>,
	"linux-riscv@lists.infradead.org"
	<linux-riscv@lists.infradead.org>,
	Palmer Dabbelt <palmer@sifive.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: RE: [PATCH 3/4] RISC-V: Support case insensitive ISA string parsing.
Date: Sat, 27 Jul 2019 00:52:59 -0700 (PDT)	[thread overview]
Message-ID: <alpine.DEB.2.21.9999.1907270043190.26998@viisi.sifive.com> (raw)
In-Reply-To: <MN2PR04MB6061790AFE4E0AAA838678028DC30@MN2PR04MB6061.namprd04.prod.outlook.com>

On Sat, 27 Jul 2019, Anup Patel wrote:

> > -----Original Message-----
> > From: Paul Walmsley <paul.walmsley@sifive.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@wdc.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