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

[Simon Glass]

Hi Graeme,

On Tue, Mar 20, 2012 at 5:39 PM, Graeme Russ <graeme.russ at gmail.com> wrote:
> Hi Simon
>
> On Wed, Mar 21, 2012 at 11:19 AM, Simon Glass <sjg at chromium.org> wrote:
>> Hi Graeme,
>>
>> On Tue, Mar 20, 2012 at 5:17 PM, Graeme Russ <graeme.russ at gmail.com> wrote:
>>> Hi Simon,
>
>>> And we are talking about one board vendor taking a SoC and using UARTA
>>> for the panic output and another board vendor deciding to use UARTB - But
>>> surely these vendors will create a separate config file for their boards.
>>
>> Nope. There is only one u-boot.bin for all boards that use this SOC.
>
> And this is what I simply don't grok - Why have a single board config for
> a range of boards that are obviously different?

That's the design goal - a single U-Boot binary for all boards that
use a particular SOC.

>
> I suppose I haven't dealt with device tree and I imagine that is what this
> is all about. But to me, device trees are a construct for a higher level
> of operation (the OS) not the boot loader (although I get that the boot
> loader can parse the device tree in order to pick up what devices are
> installed and need some kind of low-level initialisation)

Actually a device tree describes the hardware, and therefore should in
principle be just as applicable to the boot loader.

>
> I think at such a low level you really have to say 'hey, these boards are
> different and need a different configuration' unless you put something in
> hardware that allows U-Boot to pick up on the difference without needing
> to initialise _anything_ similar to what Stephen has done to pass the
> debug UART info to Linux via a scratch register

Well we could do that, but the config is in some sense supposed to be
the device tree. We are only dealing here with a little case where
there is no device tree and want to output a message.

Regards,
Simon

>
> Regards,
>
> Graeme