linux-kernel - Re: [PATCH -fixes] riscv: cpufeature: Do not drop Linux-internal extensions

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Message-ID: <20240719-deity-squander-e17b4dfed649@spud>
Date: Fri, 19 Jul 2024 09:25:04 +0100
From: Conor Dooley <conor@...nel.org>
To: Clément Léger <cleger@...osinc.com>
Cc: Andrew Jones <ajones@...tanamicro.com>,
	Samuel Holland <samuel.holland@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	linux-riscv@...ts.infradead.org, Albert Ou <aou@...s.berkeley.edu>,
	Andy Chiu <andy.chiu@...ive.com>,
	Charlie Jenkins <charlie@...osinc.com>,
	Evan Green <evan@...osinc.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -fixes] riscv: cpufeature: Do not drop Linux-internal
 extensions

On Fri, Jul 19, 2024 at 09:11:20AM +0200, Clément Léger wrote:
> 
> 
> On 18/07/2024 23:57, Andrew Jones wrote:
> > On Thu, Jul 18, 2024 at 02:29:59PM GMT, Samuel Holland wrote:
> >> The Linux-internal Xlinuxenvcfg ISA extension is omitted from the
> >> riscv_isa_ext array because it has no DT binding and should not appear
> >> in /proc/cpuinfo. The logic added in commit 625034abd52a ("riscv: add
> >> ISA extensions validation callback") assumes all extensions are included
> >> in riscv_isa_ext, and so riscv_resolve_isa() wrongly drops Xlinuxenvcfg
> >> from the final ISA string. Instead, accept such Linux-internal ISA
> >> extensions as if they have no validation callback.
> > 
> > This assumes we'll never need a validation callback for a Linux-internal
> > ISA extension. We can make that assumption now and change our mind
> > later, but we could also add Xlinuxenvcfg to riscv_isa_ext now and
> > modify the places where it matters (just print_isa?). If we add
> > Xlinuxenvcfg to the array with a NULL name then we could do something
> > like
> > 
> >  print_isa()
> >  {
> >     for (...) {
> >         ...
> >         if (!riscv_isa_ext[i].name)
> > 	   continue;
> >     }
> >  }
> 
> I would rather add it to the riscv_isa_ext[] array and avoid handling it
> differently. There is already the xandespmu extension in this array so
> xlinuxenvcfg can be added as well.

xandespmu and xlinuxenvcfg are fundamentally different, the former is
parsed from devicetree and is a real extension. xlinuxengcfg is an
internal flag. I don't think we should be printing it.

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