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

[Simon Glass]

Hi Tom,

On Tue, May 14, 2013 at 2:21 PM, Tom Rini <trini at ti.com> wrote:
> 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.

So are you saying that you are keen on the autoconf idea?

>
> --
> Tom

Regards,
Simon