[PATCH 0/3] ARM: Meson6: enable SMP

[Carlo Caione]

On Thu, Oct 2, 2014 at 5:50 PM, Arnd Bergmann <arnd at arndb.de> wrote:
> On Thursday 02 October 2014 17:38:04 Maxime Ripard wrote:
>> On Thu, Oct 02, 2014 at 05:26:53PM +0200, Arnd Bergmann wrote:
>> > On Thursday 02 October 2014 16:54:26 Maxime Ripard wrote:
>> > > On Thu, Oct 02, 2014 at 04:44:20PM +0200, Arnd Bergmann wrote:
>> > > > On Tuesday 30 September 2014 22:45:38 Carlo Caione wrote:
>> > > > > On mar, set 30, 2014 at 12:22:21 +0200, Arnd Bergmann wrote:
>> > > > > > On Tuesday 30 September 2014 10:46:46 Carlo Caione wrote:
>> > > > > > > On mar, set 30, 2014 at 10:43:52 +0200, Carlo Caione wrote:
>> > > > > > > > Amlogic Meson6 is a dual-core Cortex-A9. This patchset adds all the necessary
>> > > > > > > > pieces to boot the secondary CPU.
>> > > > > > >
>> > > > > > > Sorry for the double sending.
>> > > > > > > Forgot to CC LAKML.
>> > > > > >
>> > > > > > Looks good to me in principle, but I wonder about the CPU enable method.
>> > > > > > Are you able to implement PSCI in u-boot like it was done for allwinner?
>> > > > > >
>> > > > > > This is mostly a question of whether the system comes up in secure mode
>> > > > > > or non-secure mode.
>> > > > >
>> > > > > I would be able if I had the u-boot source code or the possibility to
>> > > > > flash the board I'm using. Unfortunately at this moment I don't have
>> > > > > either. Probably in the near future I'll be able to implement PSCI in
>> > > > > u-boot since Amlogic is kindly starting to provide documentation but now
>> > > > > this is the best I can do.
>> > > >
>> > > > Ok, I see. Let's give Amlogic some more time then. I think it's better
>> > > > to merge other parts of the platform first when we can reasonably assume
>> > > > that we don't have to change the binding any more.
>> > > >
>> > > > It would be a shame to merge this now and then make it obsolete by
>> > > > implementing PSCI but still having to carry around the original code
>> > > > for compatibility reasons.
>> > >
>> > > More likely, PSCI is not going to be supported by the bootloaders of
>> > > the devices already in the wild, so we still have to provide them an
>> > > option. And even when it will, you'll still have to support both the
>> > > devices with the old bootloaders, and the one with the new.
>> >
>> > It depends on how common the old boot loaders are, and whether it's
>> > possible to upgrade them. If we can get to the point where you can
>> > boot a kernel with a single CPU and have an easy way to update the
>> > boot loader, we don't need to support it.
>>
>> I thought I heard Olof at some point ranting about this kind of
>> requirements, but ok
>>
>> Still, holding off until something that hypothetical happens looks a
>> bit odd, doesn't it?
>
> I was mainly trying to follow what you are doing in mach-sunxi, but maybe
> I misunderstood what your plans are for PSCI support there.
>
> mach-meson is still in a very early stage, and it's not like SMP support
> is the most important feature missing from it. If there are good reasons
> to include the current patches in 3.19, we can do that.

I agree with Maxime. The problem is that I have no idea whether in the
future we will have access to all the pieces of information to replace
the bootloader to upgrade it. Realistically it's not the most
important feature but I don't think things are going to change anytime
soon. Moreover I highly doubt that people are willing to upgrade the
bootloader on their devices just to boot the mainline kernel with full
SMP support and the better we can do is to give people the chance to
use a mainline kernel on their device at full speed without risking to
throw the device away.

-- 
Carlo Caione