On Sun, Jan 9, 2022 at 1:51 AM Gabriel L. Somlo <gsomlo@xxxxxxxxx> wrote: > > On Sat, Jan 08, 2022 at 07:47:32PM +0200, Andy Shevchenko wrote: > > On Sat, Jan 8, 2022 at 3:20 PM Gabriel L. Somlo <gsomlo@xxxxxxxxx> wrote: > > > On Sat, Jan 08, 2022 at 01:26:08PM +0200, Andy Shevchenko wrote: > > > > On Sat, Jan 8, 2022 at 3:57 AM Gabriel L. Somlo <gsomlo@xxxxxxxxx> wrote: > > > > > On Sat, Jan 08, 2022 at 01:54:07AM +0200, Andy Shevchenko wrote: > > > > > > On Saturday, January 8, 2022, Gabriel Somlo <gsomlo@xxxxxxxxx> wrote: > > > > ... > > > > > > > > + u32 div; > > > > > > + > > > > > > + div = freq ? host->ref_clk / freq : 256U; > > > > > > > > > > > > + div = roundup_pow_of_two(div); > > > > > > + div = clamp(div, 2U, 256U); > > > > > > > > > > > > Logically seems to me that you may join these two together, because clamped > > > > > > range is power-of-2 one. > > > > > > > > > > `div` needs to be a power-of-2 when written to the LITEX_PHY_CLOCKERDIV > > > > > register (below). And clamp() will just enforce a min/max range, so if > > > > > (div = ref_clk / freq) ends up e.g., 5, I need both roundup_pow_of_two() > > > > > to bump it to 8, and clamp() to enforce that it's between 2 and 256. > > > > > > > > > > Unless you mean I should simply write it like: > > > > > > > > > > div = clamp(roundup_pow_of_two(div), 2U, 256U); > > > > > > > > > > ... as a single line? > > > > > > > > Yes, that's what I meant. > > > > > > Turns out, clamp really hates being passed roundup_pow_of_two() > > > directly (see below). I think it's probably better if we leave > > > them as-is, to avoid going the explicit cast route which Geert > > > recommended against. > > > > I see, then ignore my comment on this matter in v9. > > Perhaps add a comment in the code explaining that roundup_pow_of_two() > > may not be unified with clamp()? > > I worry that commenting on why things are not done some other way at > that location would detract from the legibility of the code itself. > > Perhaps we could use a cast after all, and write it out like this: > > div = clamp((u32)roundup_pow_of_two(div), 2U, 256U); > > which compiles fine without any warnings, accomplishes your "do it in > a single line" desired behavior, and doesn't require me commenting on > which linux library functions do or don't work well with others... :) We may survive without comment, it's not a big deal. > Geert, what do you think? -- With Best Regards, Andy Shevchenko
