Multi-platform, and secure-only ARM errata workarounds

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Tue, Feb 26, 2013 at 10:23:26AM +0000, Arnd Bergmann wrote:
> On Monday 25 February 2013, Stephen Warren wrote:
> > Is there any other alternative I'm not seeing? Having the kernel
> > suddenly become incompatible with any currently extant bootloader when I
> > enable CONFIG_MULTIPLATFORM doesn't seem like a great idea.
> 
> Could we make those errata be run-time enabled only when not booting
> in secure mode?

The long and the short answer to this is... no.

1. It is impossible to tell whether we're running secure or non-secure.

2. Errata need to be applied before the MMU is initialized.  We need the
   MMU to be initialized to run any C code what so ever, so calling out
   to platform specific code to set errata is not possible.  Moreover,
   we no longer determine the platform in the assembly code since DT
   came along: this was removed because detecting it in DT from assembly
   is far from trivial (you'd need to write an assembly DT parser).

Now, as for having the secure mode errata enabled on a kernel running in
non-secure mode... what happens today is that we check whether something
before the kernel has enabled the workaround, and we omit to write to
the register.

What that means is that we expect whatever came before the kernel to have
appropriately enabled the bits in the secure registers.  If it hasn't,
and you have one of these secure mode workarounds enabled, the kernel
will fault at boot time.

So, if Stephen has working configs with these secure mode workarounds
enabled, this means that the bits in the secure registers must already
be appropriately set.

Could the problem be that someone has made all errata workarounds, even
those which apply after the system is up and running, depend on
!MULTIPLATFORM ?