[RFC PATCHv4] ARM: mvebu: use dt_fixup to provide fallback for enable-method

[chris.packham@alliedtelesis.co.nz (Chris Packham)]

We need to maintain backwards compatibility with device trees that don't
define an enable method. At the same time we want the device tree to be
able to specify an enable-method and have it stick.

Previously by having smp assigned in the DT_MACHINE definition this
would be picked up by setup_arch() and override whatever
arm_dt_init_cpu_maps() had configured. Now we move the initial
assignment of default smp_ops to a dt_fixup and let
arm_dt_init_cpu_maps() override that if the device tree defines an
enable-method.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
---
Hi,

For those loosing track

v1: http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/300182.html
v2: http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/300480.html
v3: http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/302945.html

(snip)
>>> Instead of inserting something into the device tree I could just call
>>> set_smp_ops here. That might be safer than trying to insert something
>>> into the device tree.
>>
>> I don't think this is necessary. Injecting something in the DT is
>> safe, u-boot does that at every boot :)
>>
>
> Actually I thought a bit more about this option this morning. What I'm
> trying to do is provide a fallback that defines smp_ops when there isn't
> an enable-method in the device tree. I don't actually need do do
> anything to the incoming device tree, I don't even need to look at it. I
> can unconditionally call set_smp_ops() and if the device tree has an
> enable-method it will override whatever has been configured. If the
> device tree doesn't define an enable-method it will use the default that
> I've configured here. That's actually very little code and can all be
> contained in board-v7.c.

I'm pretty happy with this incarnation. It doesn't touch core code. It provides
a fallback for old device trees and it achieves my original goal of allowing
the device tree to configure the smp_ops via the enable-method property. 

 arch/arm/mach-mvebu/board-v7.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-mvebu/board-v7.c b/arch/arm/mach-mvebu/board-v7.c
index b2524d6..a4ece42 100644
--- a/arch/arm/mach-mvebu/board-v7.c
+++ b/arch/arm/mach-mvebu/board-v7.c
@@ -184,6 +184,11 @@ static void __init mvebu_dt_init(void)
 	of_platform_populate(NULL, of_default_bus_match_table, NULL, NULL);
 }
 
+static void __init armada_370_xp_dt_fixup(void)
+{
+	smp_set_ops(smp_ops(armada_xp_smp_ops));
+}
+
 static const char * const armada_370_xp_dt_compat[] = {
 	"marvell,armada-370-xp",
 	NULL,
@@ -192,11 +197,11 @@ static const char * const armada_370_xp_dt_compat[] = {
 DT_MACHINE_START(ARMADA_370_XP_DT, "Marvell Armada 370/XP (Device Tree)")
 	.l2c_aux_val	= 0,
 	.l2c_aux_mask	= ~0,
-	.smp		= smp_ops(armada_xp_smp_ops),
 	.init_machine	= mvebu_dt_init,
 	.init_irq       = mvebu_init_irq,
 	.restart	= mvebu_restart,
 	.dt_compat	= armada_370_xp_dt_compat,
+	.dt_fixup	= armada_370_xp_dt_fixup,
 MACHINE_END
 
 static const char * const armada_375_dt_compat[] = {
-- 
2.2.0.rc0