arm: mach-mvebu: dts: enable-method is always overwritten

[ylefloch@online.net (Yves Lefloch)]

Hello everybody,

I'm facing an issue that I believe to be a conflict between device-tree and 
machine_desc.

My platform is arm/mach-mvebu. I have a DT based on "armada-xp-db-dxbc2.dts" (I 
just included it and added a few okays), my CPU is a Marvell Bobcat2 switching 
chip. My kernel is a vanilla 4.16.

Everything works fine except that my second core won't boot: `CPU1: failed to 
come online'.
I tracked down the problem to arch/arm/mach-mvebu/platsmp.c: in this file is 
defined a machine_desc that hardcodes the SMP ops to `marvell,armada-xp-smp' 
whereas my device tree (by including armada-xp-98dx3236.dtsi) attempts to set 
the ops to `marvell,98dx3236-smp' through enable-method. In setup_arch() the 
machine_desc's ops overwrites the enable-method's ops, causing the wrong 
smp_boot_secondary() call to be issued.

Now there is a note from 2014 saying that this machine_desc's `smp' field is 
hardcoded like that because of "old Device Trees that were not specifying the 
cpus enable-method property". As far as I can tell, this is still the case, for 
instance "armada-370-db.dts" doesn't have any enable-method property.

I have worked around this by commenting out `armada_xp_smp_ops.smp' but 
obviously I would prefer to keep a vanilla kernel.

So I propose to:
- Add `enable-method = "marvell,armada-xp-smp"' to armada-370-xp.dtsi, because 
it seems that all Armada 370/XP include it;
- Remove the `smp' field of `armada_xp_smp_ops'.

If you agree with the diagnosis and the proposed fix I will write a patch.

Regards,
Yves Lefloch.