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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Rob Herring <robh@kernel.org>, nramas <nramas@linux.microsoft.com>
Cc:     Geert Uytterhoeven <geert@linux-m68k.org>,
        Mimi Zohar <zohar@linux.ibm.com>,
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Subject: Re: [PATCH v19 05/13] of: Add a common kexec FDT setup function
In-Reply-To: <CAL_JsqJEucP043eViq0Y1kAeqWNTqP5fLjfjz7+ksYx7QP_V5w@mail.gmail.com>
References: <20210221174930.27324-1-nramas@linux.microsoft.com>
 <20210221174930.27324-6-nramas@linux.microsoft.com>
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 <CAL_JsqJ2x7zbyP3fAacdfHOWjCVjg6XhraV2YkoBJdZ2jXAMEA@mail.gmail.com>
 <54efb4fce5aac7efbd0b1b3885e9098b1d4ea745.camel@linux.microsoft.com>
 <CAL_JsqJEucP043eViq0Y1kAeqWNTqP5fLjfjz7+ksYx7QP_V5w@mail.gmail.com>
Date:   Wed, 16 Jun 2021 12:23:44 +1000
Message-ID: <87y2basg27.fsf@mpe.ellerman.id.au>
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Rob Herring <robh@kernel.org> writes:
> On Tue, Jun 15, 2021 at 10:13 AM nramas <nramas@linux.microsoft.com> wrote:
>>
>> On Tue, 2021-06-15 at 08:01 -0600, Rob Herring wrote:
>> > On Tue, Jun 15, 2021 at 6:18 AM Geert Uytterhoeven <
>> > geert@linux-m68k.org> wrote:
>> > >
>> > > > +void *of_kexec_alloc_and_setup_fdt(const struct kimage *image,
>> > > > +                                  unsigned long
>> > > > initrd_load_addr,
>> > > > +                                  unsigned long initrd_len,
>> > > > +                                  const char *cmdline, size_t
>> > > > extra_fdt_size)
>> > > > +{
>> > > > +       /* Did we boot using an initrd? */
>> > > > +       prop = fdt_getprop(fdt, chosen_node, "linux,initrd-
>> > > > start", NULL);
>> > > > +       if (prop) {
>> > > > +               u64 tmp_start, tmp_end, tmp_size;
>> > > > +
>> > > > +               tmp_start = fdt64_to_cpu(*((const fdt64_t *)
>> > > > prop));
>> > > > +
>> > > > +               prop = fdt_getprop(fdt, chosen_node,
>> > > > "linux,initrd-end", NULL);
>> > > > +               if (!prop) {
>> > > > +                       ret = -EINVAL;
>> > > > +                       goto out;
>> > > > +               }
>> > > > +
>> > > > +               tmp_end = fdt64_to_cpu(*((const fdt64_t *)
>> > > > prop));
>> > >
>> > > Some kernel code assumes "linux,initrd-{start,end}" are 64-bit,
>> > > other code assumes 32-bit.
>> >
>> > It can be either. The above code was a merge of arm64 and powerpc >> > both
>> > of which use 64-bit and still only runs on those arches. It looks >> > like
>> > some powerpc platforms may use 32-bit, but this would have been >> > broken
>> > before.

>> of_kexec_alloc_and_setup_fdt() is called from elf_64.c (in
>> arch/powerpc/kexec) which is for 64-bit powerpc platform only.
>
> 64-bit PPC could be writing 32-bit property values. The architecture
> size doesn't necessarily matter. And if the values came from the
> bootloader, who knows what size it used.
>
> This code is 32-bit powerpc only?:
>
> arch/powerpc/boot/main.c-       /* Tell the kernel initrd address via device tree */
> arch/powerpc/boot/main.c:       setprop_val(chosen, "linux,initrd-start", (u32)(initrd_addr));
> arch/powerpc/boot/main.c-       setprop_val(chosen, "linux,initrd-end", (u32)(initrd_addr+initrd_size));

Historically that code was always built 32-bit, even when used with a
64-bit kernel.

These days it is also built 64-bit (for ppc64le).

It looks like the drivers/of/fdt.c code can handle either 64 or 32-bit,
so I guess that's why it seems to be working.

Although I'm not sure how much testing the 64-bit case gets, because the
distros tend to just use the vmlinux.

cheers