[U-Boot] [PATCH v3 0/16] Provide a mechanism to avoid using #ifdef everywhere

[Tom Rini]

On Mon, May 13, 2013 at 03:12:07PM -0700, Simon Glass wrote:
> Hi Tom,
> 
> On Thu, Mar 21, 2013 at 7:38 AM, Tom Rini <trini at ti.com> wrote:
> > On Tue, Feb 26, 2013 at 08:10:53AM -0800, Simon Glass wrote:
> >
> >> Many parts of the U-Boot code base are sprinkled with #ifdefs. This makes
> >> different boards compile different versions of the source code, meaning
> >> that we must build all boards to check for failures. It is easy to misspell
> >> an #ifdef and there is not as much checking of this by the compiler. Multiple
> >> dependent #ifdefs are harder to do than with if..then..else. Variable
> >> declarations must be #idefed as well as the code that uses them, often much
> >> later in the file/function. #ifdef indents don't match code indents and
> >> have their own separate indent feature. Overall, excessive use of #idef
> >> hurts readability and makes the code harder to modify and refactor. For
> >> people coming newly into the code base, #ifdefs can be a big barrier.
> >>
> >> The use of #ifdef in U-Boot has possibly got a little out of hand. In an
> >> attempt to turn the tide, this series includes a patch which provides a way
> >> to make CONFIG macros available to C code without using the preprocessor.
> >> This makes it possible to use standard C conditional features such as
> >> if/then instead of #ifdef. A README update exhorts compliance.
> >
> > OK, this is true.  Looking over the series, a number of the patches are
> > just general fixes / improvements that don't depend on the autoconf_...
> > work.  Lets split this out now and take them in now as they seem like
> > reviewable by inspection code.
> 
> Well sorry I didn't make time to get this done last time. I can do
> this now or...
> 
> >
> > For the approach itself, I'm not sure which is best here.  In a lot of
> > cases we're trading an #ifdef for adding a level of indent to already
> > pretty indented code and that feels like a wash, in terms of readability
> > to me.  We probably need to re-factor some of the code in question there
> > too for readability, then see about using autoconf_... type things, or
> > maybe something else.
> 
> I think you are saying to do the rearrangement and clean-up first,
> then add autoconf afterwards. I can do that but really I am wondering
> what you think of the autoconf concept? The Kconfig stuff is related
> here too, but first I would like to decide on what to do with the
> #ifdefs.

I think a lot of our #ifdefery is a problem of code that's in need of
some love and re-org and cleaning and updating.  One of the old style
rules I still try and follow is that after a few levels of indent code
doesn't read well.  Also big nested #ifdefs don't read well.  So we're
trading one in for the other.  But your series showed a lot of places
where we can re-factor things to improve readability.  So lets go that
way.  Then we can see if there's still things to improve on, and what
dead code we still have around.

-- 
Tom
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