On 04.07.2013 19:28, Nicolas Pitre wrote:

On Thu, 4 Jul 2013, Daniel Mack wrote:

quoted

In short, devices that have been deployed in quantities come in three
hardware variants, which all boot with a unique machine-id. We ship
kernel images that have board support for all three machine types, and
do minor fixups to platform data of some drivers at runtime, depending
on the board revision number (passed in via ATAGs).

What you describe above more or less fits the definition of what I 
called the "impedance matcher".  However it doesn't need to be part of 
the kernel at all.  But you should make it into a separate binary.

Please have a look at the bottom of this post for a more comprehensive 
description: http://article.gmane.org/gmane.linux.ports.arm.kernel/242929

FWIW, I gave that approach a try today for a PXA based hardware
platform, and in fact it seems to work very well. Thanks again for
sharing the idea.

In case anyone is interested, the repository is here:

  https://github.com/zonque/pxa-impedance-matcher

As the README says, it's completely specific to my use case, but maybe
anyone can use the code base to spin a different version for a different
board.


Daniel