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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 15 Jun 2021 20:48:05 +0200
Message-ID: <CAMuHMdXtT1L3yfzkTkbhqz3zgUQj89Bcm7mqz+m126NprAsK8Q@mail.gmail.com>
Subject: Re: [PATCH v4 5/5] RISC-V: Add crash kernel support
To:     Nick Kossifidis <mick@ics.forth.gr>
Cc:     linux-riscv <linux-riscv@lists.infradead.org>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>
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Hi Nick,

On Tue, Jun 15, 2021 at 8:29 PM Nick Kossifidis <mick@ics.forth.gr> wrote:
> Στις 2021-06-15 16:19, Geert Uytterhoeven έγραψε:
> > This does not match
> > https://github.com/devicetree-org/dt-schema/blob/master/schemas/chosen.yaml#L77:
> >
> >     $ref: types.yaml#/definitions/uint64-array
> >     maxItems: 2
> >     description:
> >       This property (currently used only on arm64) holds the memory
> > range,
> >       the address and the size, of the elf core header which mainly
> > describes
> >       the panicked kernel\'s memory layout as PT_LOAD segments of elf
> > format.
> >
> > Hence "linux,elfcorehdr" should be a property of the /chosen node,
> > instead of a memory node with a compatible value of "linux,elfcorehdr".
> >
>
> That's a binding for a property on the /chosen node, that as the text
> says it's defined for arm64 only and the code that handled it was also

That doesn't mean it must not be used on other architectures ;-)
Arm64 was just the first one to use it...

> on arm64. Instead the reserved-region binding I used is a standard
> binding, if you don't like the name used for the compatible string
> because it overlaps with that property we can change it. I want to use a
> reserved-region for this because we'll have to reserve it anyway so
> using a property on /chosen and then using that property to reserve the
> region seemed suboptimal.
>
> >> v2:
> >>  * Use linux,usable-memory on /memory instead of a new binding
> >
> > This part seems to have been removed in v3 and later?
> > Note that "linux,usable-memory-range" should be a property of the
> > /chosen node, too, cfr.
> > https://github.com/devicetree-org/dt-schema/blob/master/schemas/chosen.yaml#L85
> >
>
> No special handling is needed when using linux,usable-memory on /memory,
> limiting the available memory is handled by generic code at
> drivers/of/fdt.c

It was my understanding both properties under /chosen are the
recommended methods for new platforms... Let's see what Rob has
to say...

Anyway, I sent a patch series to switch to generic "linux,elfcorehdr"
handling
https://lore.kernel.org/r/cover.1623780059.git.geert+renesas@glider.be/

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds