arm: mvebu: Kirkwood boards are broken by commit 6fe50e3

[Tony Dinh]

Hi Tom,

On Thu, Jun 19, 2025 at 2:27 PM Tom Rini <trini at konsulko.com> wrote:
>
> On Thu, Jun 19, 2025 at 01:37:53PM -0700, Tony Dinh wrote:
> > Hi Jerome,
> >
> > While fixing some ext4 file system problems on 2025.07-rc4, I ran into
> > a problem booting a few Kirkwood boards. kwboot loaded the u-boot
> > image,
> > and then u-boot execution was frozen without anything going to the
> > serial console. I did a bisect and found the commit that caused it.
> >
> > https://github.com/trini/u-boot/commit/6fe50e39508043f386fc1bd40bbc02b8a75c1940
> >
> > When I tried to reverse this commit, I had a build error like this
> > "{standard input}:24246: Error: selected processor does not support
> > `mrc p15,1,r3,c15,c1,0' in Thumb mode"
> >
> > Currently, the only way to boot Kirkwood boards is to disable either
> > CONFIG_LTO or CONFIG_SYS_THUMB_BUILD or both.
> >
> > I'm using the pogo_v4 and nsa325 boards as test beds. Please let me
> > know if I can help with testing to troubleshoot this regression.
>
> I wonder if the right answer is that CONFIG_SYS_THUMB_BUILD should be
> off? A quick look around and this (and sheevaplug) are ARM926EJ-S which
> is Thumb-1 not Thumb-2 and it looks like the kernel for example only
> supports building itself with thumb2 on armv7/v7m. I know that this was
> working, so we should dig more too, but I'm not sure what the best
> answer here is.

I recalled we added support for Thumb-1 from way back and a few people
have helped porting more changes from the Linux kernel.

U-boot has grown larger and larger over the years, especially with
bootstd enabled (I know you have been watching closely for size
growth). Built without CONFIG_SYS_THUMB_BUILD, the sheevaplug board is
about 107K over the CONFIG_BOARD_SIZE_LIMIT of 512K. And it would be
an unpleasant surprise to see size growth for other downstream
projects still supporting Kirkwood SoCs.

All the best,
Tony

>
> --
> Tom