Re: [PATCH 09/11] clk: lpc32xx: add common clock framework driver

[Arnd Bergmann <arnd@arndb.de>]

On Friday 20 November 2015 20:07:46 Vladimir Zapolskiy wrote:
> On 20.11.2015 16:04, Arnd Bergmann wrote:
> > On Friday 20 November 2015 03:05:09 Vladimir Zapolskiy wrote:
> >> +
> >> +struct clk_proto_t {
> >> +       const char *name;
> >> +       const u8 parents[LPC32XX_CLK_PARENTS_MAX];
> >> +       u8 num_parents;
> >> +       unsigned long flags;
> >> +};
> >> +
> >> +#define CLK_PREFIX(LITERAL)            LPC32XX_CLK_ ## LITERAL
> >> +#define NUMARGS(...)   (sizeof((int[]){__VA_ARGS__})/sizeof(int))
> >> +
> >> +#define LPC32XX_CLK_DEFINE(_idx, _name, _flags, ...)           \
> >> +       [CLK_PREFIX(_idx)] = {                                  \
> >> +               .name = #_name,                                 \
> >> +               .flags = _flags,                                \
> >> +               .parents = { __VA_ARGS__ },                     \
> >> +               .num_parents = NUMARGS(__VA_ARGS__),            \
> >> +        }
> >> +
> > 
> > Try to not outsmart yourself with the macros. It's better to avoid
> > string concatenation so it's possible to grep for uses of some
> > constant.
> > 
> > I would probably not use a macro at all here and just open-code the
> > entire table. If you ensure that '0' is not a valid parent, then
> > you can leave out the .num_parents field and just look for the
> > zero-termination.
> 
> Macros are here for simplicity, code size reduction and to avoid some
> stupid mistakes like different number of .parents and .num_parents.
> 
> I believe macro unwrapping in this code will add another 1000 LoC and
> will result in quite unreadable and less maintainable code.

I mean specifically the macro above:

static const struct clk_proto_t clk_proto[LPC32XX_CLK_CCF_MAX] __initconst = {
+       LPC32XX_CLK_DEFINE(XTAL, xtal, 0x0),
+       LPC32XX_CLK_DEFINE(XTAL_32K, xtal_32k, 0x0),
+
+       LPC32XX_CLK_DEFINE(RTC, rtc, 0x0, LPC32XX_CLK_XTAL_32K),
+       LPC32XX_CLK_DEFINE(OSC, osc, CLK_IGNORE_UNUSED, LPC32XX_CLK_XTAL),
+       LPC32XX_CLK_DEFINE(SYS, sys, CLK_IGNORE_UNUSED,
+               LPC32XX_CLK_OSC, LPC32XX_CLK_PLL397X),
+       LPC32XX_CLK_DEFINE(PLL397X, pll_397x, CLK_IGNORE_UNUSED,
+               LPC32XX_CLK_RTC),

can become

static const struct clk_proto_t clk_proto[] __initconst = {
	[LPC32XX_CLK_XTAL]	= { "xtal" },
	[LPC32XX_CLK_XTAL_32K]	= { "xtal_32k" },
	[LPC32XX_CLK_RTC]	= { "rtc",
			.parents = { LPC32XX_CLK_XTAL_32K, 0 } },
	[LPC32XX_CLK_OSC]	= { "osc", CLK_IGNORE_UNUSED,
			.parents = { LPC32XX_CLK_XTAL, 0 } },
	[LPC32XX_CLK_SYS]	= { "sys", CLK_IGNORE_UNUSED,
			.parents = { LPC32XX_CLK_OSC, LPC32XX_CLK_PLL397X, 0) },
	[LPC32XX_CLK_PLL397X]	= { "pll_397x", CLK_IGNORE_UNUSED,
			.parents = { LPC32XX_CLK_RTC, 0 },

Not harder to read at all, not really longer, but easier to grep for.

	Arnd