[U-Boot] [RFC PATCH] Provide a mechanism to avoid using #ifdef everywhere

[Wolfgang Denk <wd@denx.de>]

Dear Simon,

In message <CAPnjgZ38HPmOf07CMYssa1Q167sRjzDpbBUbCVMaoGdRoWESog@mail.gmail.com> you wrote:
> 
> Thanks for looking at this so closely - it's just an RFC at this
> stage, but I think it has promise.

Agreed.

> > I think config_* is not a good name to use here - it has never been a
> > reserved prefix so far, so it is IMO a bad idea to turn it into one
> > now .  We already have quite a number such variable names in the code
> > all over the place (not sure I caught them all):
...
> These are variables, so won't conflict with the function macros used
> by this patch. But maybe we should try for something like cfg_...()?

You are wrong.  This includes a number of functions, and macros, too,
for example:

	void config_sdram(const struct emif_regs *regs);
	void config_ddr_phy(const struct emif_regs *regs);
	void config_cmd_ctrl(const struct cmd_control *cmd);
	void config_ddr_data(int data_macrono, ...)
	void config_io_ctrl(unsigned long val);
	void config_ddr(unsigned int pll, unsigned int ioctrl,
	void config_data_eye_leveling_samples(u32 emif_base);
	static int config_pll_clk(enum pll_clocks index, ...)
	static int config_core_clk(u32 ref, u32 freq)
	# define config_fifo(dir, idx, addr)

And cfg_ is not much better:

	#define cfg_read(val, addr, type, op)
	#define cfg_write(val, addr, type, op)
	u16 cfg_type = 0;
	unsigned cfg_val;
	u32 *cfg_reg;
	uint    cfg_addr;
	uint    cfg_data;
	...

> I did for the 'sed' step - it was a 2-3 seconds to regenerate the header files.
> 
> Full reconfig/recompile goes from about about 30s to 34s.
> Incremental build doesn't change noticeably.

I'm mostly concerned about build time for the autobuilder, which does
full config / build cycles for all boards.  Here more than 10%
increase hurt...

> I also tried recompiling both the mainline U-Boot's main.c 100 times,
> and then this one. I could not see any time difference, which is a
> little surprising. Maybe the C compiler's DCE is pretty early in the
> the process?

This is a surprising result, indeed.

> >> +     if (config_autoboot_delay_str() && delaykey[0].str == NULL)
> >> +             delaykey[0].str = config_autoboot_delay_str();
> >
> > Hm.... constructs like these make me think about side effects.  As is,
> > your implementation does not pretect against any.  This may be
> > dangerous - you are evaluating the macro multiple times now, while
> > before it was only a defined() test, folowed by a single evaluation.

You did not comment on this remark.  I think it is something to keep
in mind!

> > And to be honest - I find the old code easier to read.

:-)

> But if you have time, please take a look at the sed scripts and the Makefile.

Sorry, but I can't find the audacity to bend my mind around these
currently ;-)

But you might have a look at "tools/scripts/define2mk.sed" and either
use this as is, or base your code on this.  I would find it good to
use the same code for the same (or so very similar) purposes.

> The background here is that I have been wondering about this for a
> while, but have never really come up with a good way (in the absence
> of a unified Kconfig) of getting a complete list of CONFIG variables.

Does not the already existing "include/autoconf.mk" contain this
information?  In any case, please check "tools/scripts/define2mk.sed"

> There was a mailing list post about this a few weeks ago. But then
> David Hendrix complained about main.c which spurred me into action,
> and I thought maybe we could just live with a brute force
> 'find/grep/sed' approach for now, rather than trying to be too clever.
> That's what I have done here.

Understood, and appreciated.

> I will come back to this when I have time - will be a week or two.

Thanks.

Best regards,

Wolfgang Denk

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