[U-Boot] [PATCH v5 3/8] ARM: add assembly routine to switch to non-secure state

[Christoffer Dall <christoffer.dall@linaro.org>]

On Fri, Sep 20, 2013 at 01:27:48AM +0530, Mj Embd wrote:
> two quick points
> (a) xen already has a mode_switch code, so AFAIK xen might not use it
> (as suggested by comment in another patch in this patch set)

For KVM the boot procedure for Hyp mode is quite clearly defined: the
kernel must be booted in Hyp mode.

I was under the impression that Xen wanted to use the same paradigm and
rely on bootloaders to switch to Hyp mode and thereby get rid of the
code in Xen.

> (b) There are 2 methods of switching from Secure to Hyp mode
> one you have proposed another implemented in xen. I was suggesting
> take the best approach
> 

Can you please be more specific?  Not everyone here knows the Xen
low-level mode switch details by heart.  As far as I know, there is only
one architecturally defined proper mode to switch from secure mode to
non-secure mode, and the state that needs to be configured for Hyp-mode
and NS-mode is well defined.  Obviously two implementation can do things
differently (different order, different programminge environment, etc.)
but that doesn't mean one is better than the other.

I think it would be more productive if you can simply look at this code
and if you think some things are done more efficiently in Xen, please
comment on that, which would be very helpful.  I'm afraid there's no
magic way to apply a block of Xen code into U-Boot wihtout manual
adjustment anyway, or the other way around for that matter.

-Christoffer