[U-Boot] [PATCH] arm: support Thumb-1 with CONFIG_SYS_THUMB_BUILD

[Stefan Roese <sr@denx.de>]

Hi Albert,

On 01.02.2015 03:55, Albert ARIBAUD wrote:
> When building a THumb-1-only target with CONFIG_SYS_THUMB_BUILD,
> some files fail to build, most of the time because they include
> mcr instructions, which only exist for Thumb-2.
> 
> Thos patch introduces a Kconfig option CONFIG_THUMB2 and uses
> it to select between Thumb-2 and ARM mode for the aforementioned
> files.
> 
> This code has been build-tested and run-tested on ED Mini V2,
> both with U-Boot and SPL.
> 
> Signed-off-by: Albert ARIBAUD <albert.u.boot@aribaud.net>

Thanks. This helped me to get Thumb-1 working on the x600 (SPEAr600
with ARM926EJS). Where I some size constraints. So for this patch:

Tested-by: Stefan Roese <sr@denx.de>

But I have another Thumb-1 related problem. I'm also including UBIFS
in my board. And this results in these errors:

{standard input}: Assembler messages:
{standard input}:695: Error: selected processor does not support Thumb mode `mrs r2,cpsr'
{standard input}:696: Error: unshifted register required -- `orr r1,r2,#128'
{standard input}:697: Error: selected processor does not support Thumb mode `msr cpsr_c,r1'
{standard input}:711: Error: selected processor does not support Thumb mode `msr cpsr_c,r2'
{standard input}:766: Error: selected processor does not support Thumb mode `mrs r2,cpsr'
{standard input}:767: Error: unshifted register required -- `orr r4,r2,#128'
{standard input}:768: Error: selected processor does not support Thumb mode `msr cpsr_c,r4'
{standard input}:782: Error: selected processor does not support Thumb mode `msr cpsr_c,r2'
make[2]: *** [fs/ubifs/super.o] Error 1
...

This is because the UBIFS code uses the atomic_foo() functions
and the bitops functions. Which call the local_irq_foo() functions.
And these include the "msr/mrs" instructions, which seem to be
unsupported in Thumb-1, similar to the "mcr" instruction.

I've "solved" this problem by adding these lines to the UBIFS
Makefile:

+# some files can only build in ARM or THUMB2, not THUMB1
+ifdef CONFIG_SYS_THUMB_BUILD
+ifndef CONFIG_HAS_THUMB2
+CFLAGS_lpt.o := -marm
+CFLAGS_lpt_commit.o := -marm
+CFLAGS_super.o := -marm
+CFLAGS_tnc.o := -marm
+CFLAGS_tnc_misc.o := -marm
+endif
+endif

But I'm not really happy with this "solution".

Another option would be to remove all the irq_off/_on stuff from
the atomic_foo() and the bitops functions. We are running in a
single-threaded environment after all in U-Boot. So there should
be no need for such synch mechanisms. But these files are copied
from Linux. And I really don't like to make changes to these files.

And ideas / comments welcome.

BTW: You can easily test this on your ED Mini board as well by
enabling UBI & UBIFS support. Then you also should see those errors.

Thanks,
Stefan