linux-kernel - Re: [PATCH v2 11/13] dt-bindings: riscv: Add Supm extension description

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Message-ID: <20251230021306.GA3094273-robh@kernel.org>
Date: Mon, 29 Dec 2025 20:13:06 -0600
From: Rob Herring <robh@...nel.org>
To: Alex Elder <elder@...cstar.com>
Cc: Guodong Xu <guodong@...cstar.com>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Paul Walmsley <pjw@...nel.org>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>,
	Yixun Lan <dlan@...too.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Samuel Holland <samuel.holland@...ive.com>,
	Anup Patel <anup@...infault.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>, Lubomir Rintel <lkundrak@...sk>,
	Yangyu Chen <cyy@...self.name>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Conor Dooley <conor@...nel.org>,
	Heinrich Schuchardt <xypron.glpk@....de>,
	Kevin Meng Zhang <zhangmeng.kevin@...ux.spacemit.com>,
	Andrew Jones <ajones@...tanamicro.com>, devicetree@...r.kernel.org,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	spacemit@...ts.linux.dev, linux-serial@...r.kernel.org
Subject: Re: [PATCH v2 11/13] dt-bindings: riscv: Add Supm extension
 description

On Fri, Dec 26, 2025 at 03:28:47PM -0600, Alex Elder wrote:
> On 12/22/25 7:04 AM, Guodong Xu wrote:
> > Add description for the Supm extension. Supm indicates support for pointer
> > masking in user mode. Supm is mandatory for RVA23S64.
> > 
> > The Supm extension is ratified in commit d70011dde6c2 ("Update to ratified
> > state") of riscv-j-extension.
> > 
> > Supm depends on either Smnpm or Ssnpm, so add a schema check to enforce
> > this dependency.
> 
> I have the same general question on this, about whether it's really
> necessary for the DT binding to enforce these requirements.  The
> RISC-V specifications are what truly defines their meaning, so I
> don't really see why the DT framework should need to enforce them.
> (That said, I'm sure there are other cases where DT enforces things
> it shouldn't have to.)

Does the specification have some way to check it? What happens if a DT 
is wrong? Are you going to require a DT update to make things right? Or 
the kernel has to work-around the error? Neither is great. So having 
this as a schema makes sense to prevent either scenario.

> 
> And now, having looked at these added binding definitions (in patches
> 07 through 11 in this series), I wonder what exactly is required for
> them to be accepted.  For the most part these seem to just be defining
> how the extensions specified for RISC-V are to be expressed in
> DT files.  It seems to be a fairly straightforward copy from the
> ratified specification(s) to the YAML format.
> 
> Who need to sign off on it?  Conor?  Paul?  DT maintainers?

I generally leave this extension mess to Conor.

Rob