Do we need to support Thumb-2 code on ARMv6T2?

[Nicolas Pitre]

On Sat, 26 Mar 2011, Tixy wrote:

> I.e. does CONFIG_THUMB2_KERNEL imply ARMv7 or newer?
> I assume this is the intent as arch/arm/Kconfig has
> 
> 	depends on CPU_V7 && !CPU_V6 && !CPU_V6K && EXPERIMENTAL
> 
> and there are no hits for the string "v6t" in the source tree

If you look at the log for commit 6e6fc998b8 which introduced that 
dependency, you'll find:

|commit 6e6fc998b8c127fe06b9350a1f16e41bfe4f109d
|Author: Dave Martin <dave.martin at linaro.org>
|Date:   Mon Dec 13 21:53:53 2010 +0100
|
|    ARM: 6533/1: Thumb-2: Make CONFIG_THUMB2_KERNEL depend on !CPU_V6
|
|    This makes sense, because Thumb-2 code can't execute on plain
|    ARMv6 processors.
|
|    This will avoid accidentally configuring a broken kernel where the
|    config otherwise would allow multiple architecture versions to
|    coexist in the same kernel.
|
|    Not adding !CPU_V5 etc., because the chance of anyone trying to
|    put v5 and v7 in the same kernel is low, and I'm not aware of
|    any mach which can do this.  These could be added later if it
|    matters.
|
|    Note that the rules may need to be refined if support for the
|    ARM1156J(F)-S processor is later added to the kernel, since this
|    processor supports the rare ARMv6T2 extensions, which add support
|    for Thumb-2 and a few other ARMv7 features.
|
|    Signed-off-by: Dave Martin <dave.martin at linaro.org>
|    Acked-by: Catalin Marinas <catalin.marinas at arm.com>
|    Acked-by: Nicolas Pitre <nicolas.pitre at linaro.org>
|    Acked-by: Santosh Shilimkar <santosh.shilimkar at ti.com>
|    Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>

So for now we don't support ARMv6T2.  However this would still be a good 
idea to add some comments next to the code that may rely on this 
presumption.


Nicolas