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

[Simon Glass]

Hi Tom,

On 6 September 2014 06:03, Tom Rini <trini at ti.com> wrote:

> On Wed, Sep 03, 2014 at 06:01:44PM -0600, Simon Glass 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).
>
> No, the point of this driver (and the similar ones that exist here and
> elsewhere) is to have something small and seperate that we know is not
> the cause of the problem.
>

Please see my other email on this thread. I'm not talking about use the
driver in full, just directly calling the driver's init and putc functions
from assembler instead of duplicating them. It seems more scaleable to me
in that we can support any driver in principle. The cost is that each
driver needs to export these two functions with a defined signature.

Regards,
Simon