Early prints on different UART's for same machine type

Early prints on different UART's for same machine type

[Mohammed, Afzal]

Hi,

This is regarding board with multiple variations using an upcoming SoC from TI.
Variation of the board is detected by reading EEPROM using I2C after
init_machine gets invoked. In one of the variation UART# used is different.
Because of this decompressor logs (and early prints) can't be captured for the
board variant using this different UART#. Our solution for this problem is to
use different mach-id for the board using different UART#. But this solution
seems to be overkill as only to capture decompressor logs, we have to use
a new machine id.

As I2C will not work at the decompressor stage, I2C can't be used to detect
the board type.

As far as I know, ATAG is not parsed in decompressor stage and so ATAG cannot
be used to determine board variant or UART#. Otherwise we will have to add
capability in decompressor to parse ATAG, detect console to be used, and
modify uncompress.h to select proper console for capturing decompressor logs.
This seems a bad solution.

Our bootloader has the capability to detect the board variant.

So the best solution for us so far seems to add a new machine id, if any
better solutions are possible, please let us know.

Regards
Afzal

Re: Early prints on different UART's for same machine type

[Paul Walmsley]

Hi

On Tue, 9 Aug 2011, Mohammed, Afzal wrote:

> This is regarding board with multiple variations using an upcoming SoC from TI.
> Variation of the board is detected by reading EEPROM using I2C after
> init_machine gets invoked. In one of the variation UART# used is different.
> Because of this decompressor logs (and early prints) can't be captured for the
> board variant using this different UART#. Our solution for this problem is to
> use different mach-id for the board using different UART#. But this solution
> seems to be overkill as only to capture decompressor logs, we have to use
> a new machine id.
> 
> As I2C will not work at the decompressor stage, I2C can't be used to detect
> the board type.
> 
> As far as I know, ATAG is not parsed in decompressor stage and so ATAG cannot
> be used to determine board variant or UART#. Otherwise we will have to add
> capability in decompressor to parse ATAG, detect console to be used, and
> modify uncompress.h to select proper console for capturing decompressor logs.
> This seems a bad solution.
> 
> Our bootloader has the capability to detect the board variant.
> 
> So the best solution for us so far seems to add a new machine id, if any
> better solutions are possible, please let us know.

You might get more feedback if you E-mail 
<linux-arm-kernel@lists.infradead.org>, rather than 
<linux-arm-kernel-bounces@lists.infradead.org>.


- Paul