[PATCH 1/2] armv8: aarch32: Execute 32-bit Linux for LayerScape platforms

[arnd@arndb.de (Arnd Bergmann)]

On Friday, September 23, 2016 3:24:12 PM CEST Robin Murphy wrote:
> On 23/09/16 15:01, Stuart Yoder wrote:
> Otherwise you can
> always simply run your own shim at EL2 to drive an AArch32 EL1 (it'll
> need to trap and translate subsequent SMC calls for e.g. PSCI).
> 
> > If there is such a requirement, it's something begging for standardization.
> > Doesn't make sense for multiple divergent approaches for switching from
> > aarch64/EL2 to aarch32/EL2.
> 
> Perhaps - I did briefly look into how hard it would be to write a proper
> SMC service handler to do this (since ATF does have a framework for such
> things), but concluded it would be more than 10 minutes' work and just
> cheated instead. It's certainly something which could be raised with the
> firmware folks.

If we end up allowing all arm64 platforms to be enabled in arch/arm,
we could perhaps create a generic implementation that does both of
those things, i.e.

- Take the arm32 kernel Image or zImage file, wrap it inside of a binary
  that implements the arm64 boot protocol.
- When that starts up, try to use the new PSCI call to jump into
  the arm32 kernel
- If PSCI failed and we are running in EL2, implement the shim
  and start the arm32 kernel in EL1 mode

	Arnd