[PATCH 1/3] ARM: debug: use kconfig choice for selecting DEBUG_LL UART

[Shawn Guo]

On Thu, Aug 18, 2011 at 05:07:12PM +0100, Will Deacon wrote:
> Hi Shawn,
> 
> On Thu, Aug 18, 2011 at 05:11:06PM +0100, Shawn Guo wrote:
> > On Tue, Aug 16, 2011 at 10:41:11PM +0100, Will Deacon wrote:
> > > Enabling CONFIG_DEBUG_LL (which is required for earlyprintk) hardwires
> > > the debug UART address into the kernel, so that we can print before the
> > > platform is initialised.
> > > 
> > > If the user inadvertently selects multiple platforms with DEBUG_LL
> > > enabled, the UART address may not be correct and will likely cause the
> > > kernel to hang in the very early stages of boot.
> > > 
> > > This patch, based on a skeleton from Russell, uses a Kconfig choice for
> > > selecting the DEBUG_LL UART, therefore allowing the user to make a
> > > choice about the supported platform when DEBUG_LL is enabled.
> > > 
> > > Cc: Linus Walleij <linus.walleij at stericsson.com>
> > > Signed-off-by: Will Deacon <will.deacon at arm.com>
> > > ---
> > >  arch/arm/Kconfig.debug |   41 ++++++++++++++++++++++++-----------------
> > >  1 files changed, 24 insertions(+), 17 deletions(-)
> > > 
> > > diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
> > > index 81cbe40..11604c9 100644
> > > --- a/arch/arm/Kconfig.debug
> > > +++ b/arch/arm/Kconfig.debug
> > > @@ -72,6 +72,30 @@ config DEBUG_LL
> > >  	  in the kernel.  This is helpful if you are debugging code that
> > >  	  executes before the console is initialized.
> > >  
> > > +choice
> > > +	prompt "Kernel low-level debugging port"
> > > +	depends on DEBUG_LL
> > > +
> > > +	config DEBUG_DC21285_PORT
> > > +		bool "Kernel low-level debugging messages via footbridge serial port"
> > > +		depends on FOOTBRIDGE
> > > +		help
> > > +		  Say Y here if you want the debug print routines to direct
> > > +		  their output to the serial port in the DC21285 (Footbridge).
> > > +		  Saying N will cause the debug messages to appear on the first
> > > +		  16550 serial port.
> > > +
> > > +	config DEBUG_CLPS711X_UART2
> > 
> > I would expect this will become a long list when other platforms start
> > adding CONFIG symbol here.  It may be a good idea to sort this list
> > in symbol from the beginning.
> 
> I'm not sure that sorting this list in alphabetical order is a good idea.
> This is a Kconfig choice, so the default value is the first one in the list
> that has its dependencies satisfied. Therefore, the ordering has a direct
> impact on the default UART selection.
> 
I'm unsure that the default UART selection makes much sense here.
When we build so many platforms into single image, it's hard to say
which one should be the default.  People anyway need to check if the
the UART selection matches the platform they are debugging on.

BTW, I just posted one patch for imx based on your series.  Are you
interested in folding it into yours?

-- 
Regards,
Shawn