[PATCH] arm/imx: use Kconfig choice for low-level debug UART selection

[Will Deacon]

On Fri, Aug 19, 2011 at 12:39:37PM +0100, Sascha Hauer wrote:
> On Fri, Aug 19, 2011 at 12:09:41PM +0100, Will Deacon wrote:
> > But it's an unfortunate hinderence to a single zImage kernel which we can
> > only solve sensibly in the generic ARM code.
> 
> My problem is that if this option is enabled the kernel will not run
> on any other SoC except the one being selected here, at least when
> earlyprintk is passed on the command line. One could argue
> that this option is for people who exactly know what they do only.
> Still there should pop up a big fat warning somewhere.

Could do - but where?

> The old i.MX way ensured that by refusing to compile the kernel with
> multi SoC support.

That's a worse solution, because now the kernel doesn't run *anywhere* if
you enable DEBUG_LL and multiple SoCs. A use case for the new method is that
you have a kernel .config file for a multi-SoC kernel which is known not to
fail early on a given board. You can enable DEBUG_LL for that board and solve
the problem. It should never be enabled for a kernel that is designed to be
portable!

> > 
> > > At least this should be a choice in Kconfig to make clear that the
> > > different low-level debug options are exclusive.
> > 
> > As Shawn pointed out, we are using a Kconfig choice so you can only select
> > one UART for low-level debug output.
> 
> Ah, ok. I didn't see that Shawns mail was a reply to your series turning
> this into a choice.

Yup - the idea is to force a single UART definition when DEBUG_LL is
enabled.

Will