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

Graeme Russ
2012-03-20T23:28:40Z

Hi Stephen, Simon,

On Wed, Mar 21, 2012 at 8:17 AM, Stephen Warren <swarren@wwwdotorg.org> wrote:
> On 03/20/2012 02:13 PM, Simon Glass wrote:
>> Hi Stephen,
>>
>> On Tue, Mar 20, 2012 at 12:57 PM, Stephen Warren <swarren@wwwdotorg.org> wrote:
>>> This works together with a kernel change that looks at the scratchpad
>>> register to determine which of the many UARTs it should use for early
>>> printing:
>>>
>>> http://www.spinics.net/lists/arm-kernel/msg154633.html
>>>
>>> Note that this configuration only affects the kernel's decompressor and
>>> earlyprintk code. Once the kernel is initialized far enough to parse the
>>> device tree, the console is initialized using information contained
>>> therein.
>>>
>>> Base on work by Doug Anderson <dianders@chromium.org>, but significantly
>>> rewritten.
>>>
>>> Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>

>
>> For the pre-console panic stuff, the point is that there may well be
>> one UART used for the console, but *we don't know which one it is!*.
>
> That's where we disagree.
>
> For each board, there is a single fixed UART that should be used for
> both pre-console panic and the "real" console later. This is fixed by
> the single static board design.

I agree - The board designer should specify a 'default' debug port which
is used for all character output prior to the 'configured' console port
being initialised.

In the 'normal' boot case, the default console should never have any output
sent to it (unless it also happens to be the 'configured' console port) as
Both U-Boot and Linux will use a pre console buffer to buffer any output
prior to the 'configured' console being available

So I think there is a clear evidence that the 'Board panic no console'
and 'Specify debugging serial port at boot' are intrinsicly related - Both
U-Boot and Linux should be dumping their 'pre-console' messages to the
same port and this port should be specified by the hardware designer

So that being the case, there should be a single CONFIG_ option which
both patches should be using

Just my 2% of $1.00 ;)

Regards,

Graeme