[PATCH] of/fdt: Remove PPC32 longtrail hack in memory scan

[Michael Ellerman]

Rob Herring <robh+dt at kernel.org> writes:
> On Mon, Jul 30, 2018 at 4:47 AM Michael Ellerman <mpe at ellerman.id.au> wrote:
>> Rob Herring <robh+dt at kernel.org> writes:
>> > On Thu, Jul 26, 2018 at 11:36 PM Michael Ellerman <mpe at ellerman.id.au> wrote:
>> >> When the OF code was originally made common by Grant in commit
>> >> 51975db0b733 ("of/flattree: merge early_init_dt_scan_memory() common
>> >> code") (Feb 2010), the common code inherited a hack to handle
>> >> PPC "longtrail" machines, which had a "memory at 0" node with no
>> >> device_type.
>> >>
>> >> That check was then made to only apply to PPC32 in b44aa25d20e2 ("of:
>> >> Handle memory at 0 node on PPC32 only") (May 2014).
>> >>
>> >> But according to Paul Mackerras the "longtrail" machines are long
>> >> dead, if they were ever seen in the wild at all. If someone does still
>> >> have one, we can handle this firmware wart in powerpc platform code.
>> >>
>> >> So remove the hack once and for all.
>> >
>> > Yay. I guess Power Macs and other quirks will never die...
>>
>> Not soon.
>>
>> In base.c I see:
>>  - the hack in arch_find_n_match_cpu_physical_id()
>>    - we should just move that into arch code, it's a __weak arch hook
>>      after all.
>
> Except then we'd have to export __of_find_n_match_cpu_property. I
> somewhat prefer it like it is because arch specific functions tend to
> encourage duplication. But if the implementation is completely
> different like sparc, then yes, a separate implementation makes sense.

OK I'll leave it as-is then.

>>  - a PPC hack in of_alias_scan(), I guess we need to retain that
>>    behaviour, but it's pretty minor anyway.
>
> It would be nice to know what platform(s) needs this as I don't have a
> clue.

Yeah.

> It would also be nice if I had some dumps of DTs for some of
> these OpenFirmware systems.

Yeah it would. What if I threw some in a git tree somewhere?

I guess fully unpacked is the most useful form, ie. just a direct copy
from /proc/device-tree.

cheers