[U-Boot] [PATCH v3 5/6] arm: debug: add Kconfig entries for lowlevel debug

[Masahiro Yamada]

Hi Simon,


On Wed, 3 Sep 2014 18:01:44 -0600
Simon Glass <sjg at chromium.org> wrote:

> Hi Masahiro,
> 
> On 31 August 2014 20:06, Masahiro Yamada <yamada.m at jp.panasonic.com> wrote:
> > We have not had a good method to debug the early boot stage such as
> > lowlevel_init function.  I guess developers generally use dedicated
> > debuggers for that, but it is difficult in some cases.
> > (For example, my debugger cannot connect to the ARM processor when
> > it is in the secure state.  It sometimes happens when I need to
> > debug the early boot stage on ARM SoCs with secure extension.)
> >
> > The low level debug feature in Linux would be also helpful for U-boot
> > when we are stucking in nasty problems where the console is not
> > available yet.
> >
> > You have to enable CONFIG_DEBUG_LL to use this feature.
> > For now, only 8250-compatible UART devices are supported.
> > You can add a header file under arch/arm/include/debug/ directory
> > to support your UART device if necessary.
> >
> > Signed-off-by: Masahiro Yamada <yamada.m at jp.panasonic.com>
> 
> Is it possible to use the existing drivers for this? It seems
> unfortunate to duplicate the ns16550 driver (if that is what has
> happened).

I am afraid it is difficult since the serial drivers are too
complicated and written in C.
Indeed, it is unfortunate, though.

This low level debug framework only uses r0, r1, r2, r3
registers and does not need stack.

I think it has an advantage over the serial drivers
for debugging the lowlevel_init where no stack is ready.



Best Regards
Masahiro Yamada