RE: [PATCH RESEND 2/2] drivers: clk: zynqmp: update divider round rate logic

[Buddhabhatti, Jay]

Hi Stephen,

> -----Original Message-----
> From: Stephen Boyd <sboyd@xxxxxxxxxx>
> Sent: Tuesday, October 24, 2023 9:08 AM
> To: Buddhabhatti, Jay <jay.buddhabhatti@xxxxxxx>; Simek, Michal
> <michal.simek@xxxxxxx>; mturquette@xxxxxxxxxxxx
> Cc: linux-clk@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; Buddhabhatti, Jay <jay.buddhabhatti@xxxxxxx>
> Subject: Re: [PATCH RESEND 2/2] drivers: clk: zynqmp: update divider round
> rate logic
> 
> Quoting Jay Buddhabhatti (2023-10-16 04:30:02)
> > Currently zynqmp divider round rate is considering single parent and
> > calculating rate and parent rate accordingly. But if divider clock
> > flag is set to SET_RATE_PARENT then its not trying to traverse through
> > all parent rate and not selecting best parent rate from that. So use
> > common
> > divider_round_rate() which is traversing through all clock parents and
> > its rate and calculating proper parent rate.
> >
> > Signed-off-by: Jay Buddhabhatti <jay.buddhabhatti@xxxxxxx>
> > ---
> >  drivers/clk/zynqmp/divider.c | 70
> > ++++++------------------------------
> >  1 file changed, 10 insertions(+), 60 deletions(-)
> 
> Can't argue against removing that many lines!
> 
> >
> > diff --git a/drivers/clk/zynqmp/divider.c
> > b/drivers/clk/zynqmp/divider.c index 33a3b2a22659..a42c183d7e5d 100644
> > --- a/drivers/clk/zynqmp/divider.c
> > +++ b/drivers/clk/zynqmp/divider.c
> > @@ -193,23 +149,17 @@ static long zynqmp_clk_divider_round_rate(struct
> clk_hw *hw,
> >                 return DIV_ROUND_UP_ULL((u64)*prate, bestdiv);
> >         }
> >
> > -       bestdiv = zynqmp_divider_get_val(*prate, rate, divider->flags);
> > -
> > -       /*
> > -        * In case of two divisors, compute best divider values and return
> > -        * divider2 value based on compute value. div1 will  be automatically
> > -        * set to optimum based on required total divider value.
> > -        */
> > -       if (div_type == TYPE_DIV2 &&
> > -           (clk_hw_get_flags(hw) & CLK_SET_RATE_PARENT)) {
> > -               zynqmp_get_divider2_val(hw, rate, divider, &bestdiv);
> > +       max = divider->max_div;
> > +       while (max != 0) {
> > +               if ((max & 1) == 1)
> > +                       width++;
> > +               max = max >> 1;
> 
> Is this ffs()?
[Jay] We need last set bit to get max width. I will use fls() to get most significant set bit for this. Thanks for suggestion.

Thanks,
Jay
> 
> >         }
> >
> > -       if ((clk_hw_get_flags(hw) & CLK_SET_RATE_PARENT) && divider->is_frac)
> > -               bestdiv = rate % *prate ? 1 : bestdiv;
> > +       rate = divider_round_rate(hw, rate, prate, NULL, width,
> > + divider->flags);
> >
> > -       bestdiv = min_t(u32, bestdiv, divider->max_div);
> > -       *prate = rate * bestdiv;
> > +       if (divider->is_frac && (clk_hw_get_flags(hw) & CLK_SET_RATE_PARENT)
> && (rate % *prate))
> > +               *prate = rate;