linux-kernel - Re: [PATCH v4 06/11] dt-bindings: riscv: Add B ISA extension description

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Message-ID: <20260112-veal-retaliate-7cf9a2981aaf@spud>
Date: Mon, 12 Jan 2026 21:41:50 +0000
From: Conor Dooley <conor@...nel.org>
To: Guodong Xu <guodong@...cstar.com>
Cc: Rob Herring <robh@...nel.org>, 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>,
	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 v4 06/11] dt-bindings: riscv: Add B ISA extension
 description

On Sat, Jan 10, 2026 at 01:18:18PM +0800, Guodong Xu wrote:
> Add description of the single-letter B extension for Bit Manipulation.
> B is mandatory for RVA23U64.
> 
> The B extension is ratified in the 20240411 version of the unprivileged
> ISA specification. According to the ratified spec, the B standard
> extension comprises instructions provided by the Zba, Zbb, and Zbs
> extensions.
> 
> Add two-way dependency check to enforce that B implies Zba/Zbb/Zbs; and
> when Zba/Zbb/Zbs (all of them) are specified, then B must be added too.
> 
> The reason why B/Zba/Zbb/Zbs must coexist at the same time is that
> unlike other single-letter extensions, B was ratified (Apr/2024) much
> later than its component extensions Zba/Zbb/Zbs (Jun/2021).
> 
> When "b" is specified, zba/zbb/zbs must be present to ensure
> backward compatibility with existing software and kernels that only
> look for the explicit component strings.
> 
> When all three components zba/zbb/zbs are specified, "b" should also be
> present. Making "b" mandatory when all three components are present.

> Existing devicetrees with zba/zbb/zbs but without "b" will generate
> warnings that can be fixed in follow-up patches.

Are you going to send these fixup patches for other devicetrees? The
majority appear to be other spacemit devices.

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