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

[andrew@lunn.ch (Andrew Lunn)]

On Fri, Jun 08, 2018 at 05:43:11PM +0200, Yves Lefloch wrote:
> Hello everybody,

Adding Chris Packham. He did some work in this area.

       Andrew

> 
> 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.