[U-Boot] [PATCH] 7/12 Multiadapter/multibus I2C, drivers part 4

[Wolfgang Denk]

Dear ksi at koi8.net,

In message <Pine.LNX.4.64ksi.0902181112400.5002 at home-gw.koi8.net> you wrote:
> 
> > Duplicating the source code (and thus the object code, too) to create
> > additional instances of basicly the same driver seems to be the wrong
> > approach to me.
> > 
> > It doesn't scale well, to say the least.
> 
> It is _NOT_ the same driver. Every bitbaged I2C driver is _DIFFERENT_. Only
> the _NAME_ is the same.

This is one way to implement it, but not the only one.

Just to give  an  example  of  a  different  implementation  (without
claiming  that that would be a better one): we could provide an array
of functions (instead of macros) for each such adapter, so  we  could
use  just  a single instance of the driver which takes the address of
the respective array as argument.

> The soft_i2c.c is _NOT_ a driver _SOURCE_. It is a _TEMPLATE_ that makes a

This is your implementation. It is not the  only  possible  implemen-
tation.  Please  try  and  open  your  mind  to  discuss  alternative
possibilities as well.

> And it can _NOT_ scale because it is impossible to make a generic driver
> _SOURCE_ for each and every hardware configuration imaginable. That existing

Impossible. Famous last words.

> soft_i2c.c makes _GENERATION_ of such a driver trivial. The only problem
> with it is it only makes _ONE_ such interface.

And it duplicates the source code for each additional instance that is
needed.

> And no, we are _NOT_ duplicating source code. Source code is _DIFFERENT_ for
> different adapters. We just creating several _INSTANCES_ using that template
> with _DIFFERENT_ parameters. And those instances are all different. The
> template itself does _NOT_ go into the final code.

Call it what you want, I call it duplication of code.

> > Is this theory or did you perform code size measurements?
> 
> It is obvious. Furthermore, it doesn't make sence to count size difference
> here because it is miniscule -- how many I2C adapters do we have on a board?

It is obvious. Famous last words again.


> The former does not require additional adapter struct member, hwadap_no.
> And, unlike the latter, it is self-contained, it doesn't require any
> external global variable to decide what to do. One can initialize all
> adapters by:
> 
> 	for (i = 0; i < NUM_I2C_ADAPTERS; i++)
> 		i2c_adap[i]->init(...);

Most probably we never *want* to initialize all adapters...


Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
CONSUMER NOTICE:  Because  of  the  "Uncertainty  Principle,"  It  Is
Impossible  for  the  Consumer  to  Find  Out  at  the Same Time Both
Precisely Where This Product Is and How Fast It Is Moving.