Re: [PATCH v1 1/7] clk: qcom: clk-alpha-pll: Add support for Fabia PLL calibration

[Taniya Das]

Hi Stephen,

Thanks for your review.

On 11/6/2019 6:06 AM, Stephen Boyd wrote:
> Quoting Taniya Das (2019-10-31 05:21:07)
> > diff --git a/drivers/clk/qcom/clk-alpha-pll.c b/drivers/clk/qcom/clk-alpha-pll.c
> > index 055318f..8cb77ca 100644
> > --- a/drivers/clk/qcom/clk-alpha-pll.c
> > +++ b/drivers/clk/qcom/clk-alpha-pll.c
> > @@ -1141,15 +1160,11 @@ static int alpha_pll_fabia_set_rate(struct clk_hw *hw, unsigned long rate,
> >                                                  unsigned long prate)
> >   {
> >          struct clk_alpha_pll *pll = to_clk_alpha_pll(hw);
> > -       u32 val, l, alpha_width = pll_alpha_width(pll);
> > +       u32 l, alpha_width = pll_alpha_width(pll);
> >          u64 a;
> >          unsigned long rrate;
> >          int ret = 0;
> >
> > -       ret = regmap_read(pll->clkr.regmap, PLL_MODE(pll), &val);
> > -       if (ret)
> > -               return ret;
> > -
> >          rrate = alpha_pll_round_rate(rate, prate, &l, &a, alpha_width);
> >
> >          /*
>
> How is this diff related? Looks like it should be split off into another
> patch to remove a useless register read.

I will split this in different patch.

> > @@ -1167,7 +1182,66 @@ static int alpha_pll_fabia_set_rate(struct clk_hw *hw, unsigned long rate,
> >          return __clk_alpha_pll_update_latch(pll);
> >   }
> >
> > +static int alpha_pll_fabia_prepare(struct clk_hw *hw)
> > +{
>
> Why are we doing this in prepare vs. doing it at PLL configuration time?
> Does it need to be recalibrated each time the PLL is enabled?

In the case if PLL looses the configuration then we would encounter PLL 
locking issues. Thus want to go ahead with prepare. In the case it is 
calibrated it would return.

> > +       struct clk_alpha_pll *pll = to_clk_alpha_pll(hw);
> > +       const struct pll_vco *vco;
> > +       struct clk_hw *parent_hw;
> > +       unsigned long cal_freq, rrate;
> > +       u32 cal_l, regval, alpha_width = pll_alpha_width(pll);
> > +       u64 a;
> > +       int ret;
> > +
> > +       /* Check if calibration needs to be done i.e. PLL is in reset */
> > +       ret = regmap_read(pll->clkr.regmap, PLL_MODE(pll), &regval);
>
> Please use 'val' instead of 'regval' as regval almost never appears in
> this file already.

Sure, will use 'val'.

> > +       if (ret)
> > +               return ret;
> > +
> > +       /* Return early if calibration is not needed. */
> > +       if (regval & PLL_RESET_N)
> > +               return 0;
> > +
> > +       vco = alpha_pll_find_vco(pll, clk_hw_get_rate(hw));
> > +       if (!vco) {
> > +               pr_err("alpha pll: not in a valid vco range\n");
> > +               return -EINVAL;
> > +       }
> > +
> > +       cal_freq = DIV_ROUND_CLOSEST((pll->vco_table[0].min_freq +
> > +                               pll->vco_table[0].max_freq) * 54, 100);
>
> Do we need to cast the first argument to a u64 to avoid overflow?

No we do not need.

> > +
> > +       parent_hw = clk_hw_get_parent(hw);
> > +       if (!parent_hw)
> > +               return -EINVAL;
> > +
> > +       rrate = alpha_pll_round_rate(cal_freq, clk_hw_get_rate(parent_hw),
> > +                                       &cal_l, &a, alpha_width);
> > +       /*
> > +        * Due to a limited number of bits for fractional rate programming, the
> > +        * rounded up rate could be marginally higher than the requested rate.
> > +        */
> > +       if (rrate > (cal_freq + FABIA_PLL_RATE_MARGIN) || rrate < cal_freq) {
> > +               pr_err("Call set rate on the PLL with rounded rates!\n");
>
> This message is weird. Drivers shouldn't need to call set rate with
> rounded rates. What is going on?

:), my bad, copy paste from another function. I will remove this print.

> > +               return -EINVAL;
> > +       }
> > +
> > +       /* Setup PLL for calibration frequency */
> > +       regmap_write(pll->clkr.regmap, PLL_ALPHA_VAL(pll), cal_l);
> > +
> > +       /* Bringup the pll at calibration frequency */
>
> capitalize PLL.

Will take care of it.

> > +       ret = clk_alpha_pll_enable(hw);
> > +       if (ret) {
> > +               pr_err("alpha pll calibration failed\n");
> > +               return ret;
> > +       }
> > +
> > +       clk_alpha_pll_disable(hw);
> > +
> > +       return 0;
> > +}
> > +

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