linux-kernel - Re: [PATCH v5 07/16] riscv: add ISA extensions validation callback

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Date: Tue, 21 May 2024 09:58:25 +0200
From: Clément Léger <cleger@...osinc.com>
To: Conor Dooley <conor@...nel.org>
Cc: Jonathan Corbet <corbet@....net>, Paul Walmsley
 <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>,
 Albert Ou <aou@...s.berkeley.edu>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Anup Patel <anup@...infault.org>, Shuah Khan <shuah@...nel.org>,
 Atish Patra <atishp@...shpatra.org>, linux-doc@...r.kernel.org,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, kvm@...r.kernel.org,
 kvm-riscv@...ts.infradead.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v5 07/16] riscv: add ISA extensions validation callback



On 17/05/2024 18:44, Conor Dooley wrote:
> On Fri, May 17, 2024 at 04:52:47PM +0200, Clément Léger wrote:
>> Since a few extensions (Zicbom/Zicboz) already needs validation and
>> future ones will need it as well (Zc*) add a validate() callback to
>> struct riscv_isa_ext_data. This require to rework the way extensions are
>> parsed and split it in two phases. First phase is isa string or isa
>> extension list parsing and consists in enabling all the extensions in a
>> temporary bitmask (source isa) without any validation. The second step
>> "resolves" the final isa bitmap, handling potential missing dependencies.
>> The mechanism is quite simple and simply validate each extension
>> described in the source bitmap before enabling it in the resolved isa
>> bitmap. validate() callbacks can return either 0 for success,
>> -EPROBEDEFER if extension needs to be validated again at next loop. A
>> previous ISA bitmap is kept to avoid looping multiple times if an
>> extension dependencies are never satisfied until we reach a stable
>> state. In order to avoid any potential infinite looping, allow looping
>> a maximum of the number of extension we handle. Zicboz and Zicbom
>> extensions are modified to use this validation mechanism.
> 
> I wish we weren't doin' it at all, but since we have to, I think what
> you've got here is good.

Yup, this is what you got with a fast evolving architecture I guess ;)

> Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
> 
> Do you want me to send some patches for the F/V stuff we discussed
> previously?

Sure go ahead, I did not have anything written yet.

Thanks,

Clément

> 
> Cheers,
> Conor.