Re: [PATCH 1/5] clk: renesas: rcar-gen2-legacy: Switch Z clock to .determine_rate()

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Simon,

On Tue, Jun 18, 2019 at 1:09 PM Simon Horman <horms@verge.net.au> wrote:
> On Mon, Jun 17, 2019 at 02:52:34PM +0200, Geert Uytterhoeven wrote:
> > As the .round_rate() callback returns a long clock rate, it cannot
> > return clock rates that do not fit in signed long, but do fit in
> > unsigned long.  Hence switch the Z clock on R-Car Gen2 from the old
> > .round_rate() callback to the newer .determine_rate() callback, which
> > does not suffer from this limitation.
> >
> > This includes implementing range checking.
> >
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

> > --- a/drivers/clk/renesas/clk-rcar-gen2.c
> > +++ b/drivers/clk/renesas/clk-rcar-gen2.c
> > @@ -66,19 +66,22 @@ static unsigned long cpg_z_clk_recalc_rate(struct clk_hw *hw,
> >       return div_u64((u64)parent_rate * mult, 32);
> >  }
> >
> > -static long cpg_z_clk_round_rate(struct clk_hw *hw, unsigned long rate,
> > -                              unsigned long *parent_rate)
> > +static int cpg_z_clk_determine_rate(struct clk_hw *hw,
> > +                                 struct clk_rate_request *req)
> >  {
> > -     unsigned long prate  = *parent_rate;
> > -     unsigned int mult;
> > +     unsigned long prate = req->best_parent_rate;
> > +     unsigned int min_mult, max_mult, mult;
> >
> > -     if (!prate)
> > -             prate = 1;
> > +     min_mult = max(div_u64(req->min_rate * 32ULL, prate), 1ULL);
> > +     max_mult = min(div_u64(req->max_rate * 32ULL, prate), 32ULL);
>
> nit: the type of the second parameter doesn't look correct to me,
> div_u64 expects a u32 divisor.

Yes, this should use div64_ul() instead.

> > +     if (max_mult < min_mult)
> > +             return -EINVAL;
> >
> > -     mult = div_u64((u64)rate * 32, prate);
> > -     mult = clamp(mult, 1U, 32U);
> > +     mult = div_u64(req->rate * 32ULL, prate);
>
> Likewise, do we care that prate will be 64bit on 64bit platforms?
> (Yes, I know gen2 SoCs are 32bit :)

Likewise, div64_ul().

Thanks a lot!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds