linux-kernel - Re: [PATCH v19 02/13] x86/setup: Use parse_crashkernel_high

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Date:   Wed, 29 Dec 2021 17:51:29 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
Cc:     Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        Baoquan He <bhe@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        kexec@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        linux-doc@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
        Feng Zhou <zhoufeng.zf@...edance.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Chen Zhou <dingguo.cz@...group.com>,
        John Donnelly <John.p.donnelly@...cle.com>
Subject: Re: [PATCH v19 02/13] x86/setup: Use parse_crashkernel_high_low() to
 simplify code

On Wed, Dec 29, 2021 at 11:04:21PM +0800, Leizhen (ThunderTown) wrote:
> Chen Zhou and I tried to share the code because of a suggestion. After so many
> attempts, it doesn't seem to fit to make generic. Or maybe I haven't figured
> out a good solution yet.

Well, you learned a very important lesson and the many attempts are not
in vain: code sharing does not make sense in every case.

> I will put the patches that make arm64 support crashkernel...high,low to
> the front, then the parse_crashkernel() unification patches. Even if the
> second half of the patches is not ready for v5.18, the first half of the
> patches is ready.

I think you should concentrate on the arm64 side which is, AFAICT, what
you're trying to achieve.

The "parse_crashkernel() unification" needs more thought because, as I
said already, that doesn't make a whole lot of sense to me.

If you want to enforce the fact that "low" makes sense only when "high"
is supplied, parse_crashkernel_high_low() is not the right thing to do.
You need to have a *single* function which does all the parsing where
you can decide what to do: "if high, parse low", "if no high supplied,
ignore low" and so on.

And if those are supported on certain architectures only, you can do
ifdeffery...

But I think I already stated that I don't like such unifications which
introduce unnecessary dependencies between architectures. Therefore, I
won't accept them into x86 unless there's a strong compelling reason.
Which I don't see ATM.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette