linux-kernel - Re: [PATCH v4 1/7] riscv: asm: alternative-macros: Introduce ALTERNATIVE

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Date:   Thu, 24 Nov 2022 21:44:25 +0100
From:   Heiko Stübner <heiko@...ech.de>
To:     Conor Dooley <conor@...nel.org>, Conor Dooley <conor@...nel.org>
Cc:     Prabhakar <prabhakar.csengg@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Guo Ren <guoren@...nel.org>,
        Jisheng Zhang <jszhang@...nel.org>,
        Atish Patra <atishp@...osinc.com>,
        Anup Patel <apatel@...tanamicro.com>,
        Andrew Jones <ajones@...tanamicro.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Philipp Tomsich <philipp.tomsich@...ll.eu>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-renesas-soc@...r.kernel.org,
        Biju Das <biju.das.jz@...renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v4 1/7] riscv: asm: alternative-macros: Introduce ALTERNATIVE_3() macro

Am Donnerstag, 24. November 2022, 21:08:17 CET schrieb Conor Dooley:
> On 24/11/2022 20:05, Conor Dooley wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > 
> > On Thu, Nov 24, 2022 at 08:58:41PM +0100, Heiko Stübner wrote:
> >> Am Donnerstag, 24. November 2022, 20:52:33 CET schrieb Conor Dooley:
> >>> On Thu, Nov 24, 2022 at 05:22:01PM +0000, Prabhakar wrote:
> >>>> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >>>>
> >>>> Introduce ALTERNATIVE_3() macro.
> >>>
> >>> Bit perfunctory I think! There's a lovely comment down below that would
> >>> make for a better commit message if you were to yoink it.
> >>> Content looks about what I'd expect to see though.
> >>
> >> Also both the comment on the original ALTERNATIVE_2 and the new ALTERNATIVE_3
> >> should probably be merged into a single comment explaining this once for all
> >> ALTERNATIVE_x variants.
> >>
> >> Especially with the dma stuff, I'm pretty sure we'll get at least an ALTERNATIVE_4
> >> if not even more ;-) . So we defnitly don't want to repeat this multiple times.
> > 
> > Oh I can promise you that there'll be a #4 ;) I do find the comment's
> > wording to be quite odd though..
> > 
> >> + * A vendor wants to replace an old_content, but another vendor has used
> >> + * ALTERNATIVE_2() to patch its customized content at the same location. In
> > 
> > In particular this bit about "at the same location" does not make all
> > that much sense. What "at the same location" means in this context
> > should be expanded on imo. Effectively it boils down to someone else is
> > already replacing the same things you want to replace - it's just the
> > word "location" that might make sense if you're an old hand but not
> > otherwise?
> 
> Or maybe I am just biased because I tried to explain this to someone
> recently and the language in the comments didn't make sense to them,
> and anyone meddling with this code should be able to understand it?

When I first looked at the whole alternatives / patching thing, the whole thing
looked like dark magic to me ;-) .

But yeah, the comment here, but also the original one above ALTERNATIVE_2
could use improvements to explain better what it tries to do.


> >> + * this case, this vendor can create a new macro ALTERNATIVE_3() based
> > 
> > Also, using the word "can". Is it not a "must" rather than a "can",
> > since this stuff needs to be multiplatform?
> > 
> >> + * on the following sample code and then replace ALTERNATIVE_2() with
> >> + * ALTERNATIVE_3() to append its customized content.
> > 
> > 
> 
>