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

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Message-ID: <fe02eb618eee141e8bc021e8e30906fc@mailhost.ics.forth.gr>
Date:   Tue, 15 Jun 2021 21:29:40 +0300
From:   Nick Kossifidis <mick@....forth.gr>
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>,
        Rob Herring <robh+dt@...nel.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

Hello Geert,

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 
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

Regards,
Nick