[U-Boot] [PATCH] tegra: Specify debugging serial port at boot.

[Doug Anderson]

Stephen,


On Wed, Mar 21, 2012 at 9:49 AM, Stephen Warren <swarren at wwwdotorg.org> wrote:
> I was under the impression that earlyprintk was a boolean option, and
> didn't take any arguments. But, a quick grep shows that some archs do
> allow it to take an argument. The ARM code that handles the option
> doesn't process the argument at present as far as I can tell, although
> many ARM defconfigs do provide one. I'll see if it's possible to rework
> the Tegra kernel code to use any earlyprintk argument.

If you're going to look at getting earlyprintk able to take arguments,
this bug (and the associated links) might be of interest to you:
    http://code.google.com/p/chromium-os/issues/detail?id=19185

It would certainly be nice to get earlyprintk able to take arguments
on ARM in the kernel.  I didn't originally go down that route because
it seemed like there were going to be lots of yaks to shave and it
would involve changes to some of the core Linux ARM boot code.  It
also didn't solve the problem where the ARM kernel wants to do prints
before translation (as Olof points out in in the discussion thread
linked above).  ...but it does seem to be the better route.


> I doubt it will be possible to do this in the ARM zImage decompressor
> though.

The "decompressing" part of the kernel wouldn't come for free without
a lot of work, but maybe the right answer is to leverage u-boot's
ability to decompress the kernel and stop using the zImage anyway.
That would make Simon happy, I think.


-Doug