compiling 2.6.37 kernel in THUMB2 mode

[vb at vsbe.com]

On Fri, Mar 11, 2011 at 2:44 PM,  <vb at vsbe.com> wrote:
>
> boot.ok:usb 3-1.4: SerialNumber: 07A80C01174E078E
> boot.th:usb 3-1.4: SerialNumber: 07AA08011D51D473
>

oh, geez, this is embarrassing - please disregard this 'clue', but th
rest of mystery remains - linux does not boot all the way...

cheers,
/vb


> I wonder if this is an indication of some USB problems (which would
> explain why the file system fails to mount), but find it hard to come
> up with a theory.
>
> I wonder if this rings a bell with anyone,
>
> thank you in advance,
>
> Vadim
>
>
> On Fri, Feb 18, 2011 at 1:26 AM, Dave Martin <dave.martin at linaro.org> wrote:
>> On Thu, Feb 17, 2011 at 5:30 PM,  <vb at vsbe.com> wrote:
>>
>> [...]
>>
>>>
>>> Hi Dave,
>>>
>>> thank you again for the hints.
>>>
>>> I am trying to build an image for a Tegra2 based platform, it s a
>>> 2.6.37 based tree with a fair amount of private additions (to be
>>> upstreamed at some point), which does now come up and run in ARM mode.
>>> I am trying to see if it can run in Thumb mode.
>>>
>>> It looks like certain files need to be compiled in ARM mode even when
>>> THUMB2_KERNEL is enabled, but I don't see this happening in 2.6.37, I
>>> was wondering how this is done in your tree.
>>
>> Generally, this can be kept to a minimum.
>>
>> On OMAP, the low-level PM code calls into firmware which cannot cope
>> with interworking between ARM and Thumb.  The PM code on the ARM side
>> could be made to work with this even if it is mostly built in Thumb,
>> but that would be complex and not really worth the pain.
>>
>> You may have this problem if you're trying to communicate with
>> firmware, but it's best if you port everything else to be buildable in
>> Thumb-2: the primary reason is that for backwards compatibility
>> reasons, much of the assembler code in the kernel doesn't support
>> ARM/Thumb interworking either.  This means that mixing ARM and Thumb
>> code in the kernel will lead to problems unless you're careful.
>>
>>>
>>> I tried building an OMAP image, but it does not build in Thumb mode,
>>> and Thumb can't even be enabled for it because CPU_V6 configured in.
>>> So I was wondering if this tree has some other working config which
>>> does use Thumb mode. I'll look at the config files you mentioned, but
>>> any suggestions/warnings about converting a kernel to work in Thumb
>>> mode are welcome,
>>
>> Assuming you started with omap2plus_defconfig, you need to remove
>> CONFIG_ARCH_OMAP2 from the config.  It's not possible to incorporate
>> support for omap2 with CONFIG_THUMB2_KERNEL enabled because ARMv6
>> doesn't support Thumb-2.
>>
>> Here's the config I was using:
>> http://people.linaro.org/~dmart/arm_omap-thumb2+v2_config (based on
>> the linaro config-- note: you don't need to build all the modules!
>> Just make zImage or uImage)
>>
>> Hope that helps!
>> ---Dave
>>
>