linux-kernel - Re: [PATCH v4 5/5] RISC-V: Add crash kernel support

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Message-ID: <CAL_JsqLHOmZ6az0bYGC3dg__YX3aq=+Un4_x4+R2nNksc0hM2g@mail.gmail.com>
Date:   Tue, 15 Jun 2021 13:21:38 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Nick Kossifidis <mick@....forth.gr>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v4 5/5] RISC-V: Add crash kernel support

On Tue, Jun 15, 2021 at 12:48 PM Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
>
> Hi Nick,
>
> On Tue, Jun 15, 2021 at 8:29 PM Nick Kossifidis <mick@....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...

It is used on arm64 because memory is often passed by UEFI tables and
not with /memory node. As riscv is also supporting EFI, I'd think they
would do the same.

> > 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@...ux-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