linux-kernel - Re: [PATCH v2 1/3] clk: qcom: clk-alpha-pll: Add support for controlling Agera PLLs

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Message-ID: <160264125446.310579.18150875025884105137@swboyd.mtv.corp.google.com>
Date:   Tue, 13 Oct 2020 19:07:34 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Taniya Das <tdas@...eaurora.org>
Cc:     David Brown <david.brown@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andy Gross <agross@...nel.org>, devicetree@...r.kernel.org,
        robh@...nel.org, robh+dt@...nel.org,
        Taniya Das <tdas@...eaurora.org>
Subject: Re: [PATCH v2 1/3] clk: qcom: clk-alpha-pll: Add support for controlling Agera PLLs

Quoting Taniya Das (2020-10-13 10:11:48)
> diff --git a/drivers/clk/qcom/clk-alpha-pll.c b/drivers/clk/qcom/clk-alpha-pll.c
> index 26139ef..17e1fc0 100644
> --- a/drivers/clk/qcom/clk-alpha-pll.c
> +++ b/drivers/clk/qcom/clk-alpha-pll.c
> @@ -1561,3 +1571,73 @@ const struct clk_ops clk_alpha_pll_postdiv_lucid_ops = {
>         .set_rate = clk_alpha_pll_postdiv_fabia_set_rate,
>  };
>  EXPORT_SYMBOL_GPL(clk_alpha_pll_postdiv_lucid_ops);
> +
> +void clk_agera_pll_configure(struct clk_alpha_pll *pll, struct regmap *regmap,
> +                       const struct alpha_pll_config *config)
> +{
> +       if (config->l)
> +               regmap_write(regmap, PLL_L_VAL(pll), config->l);

Maybe make a helper function for this too. That way we can't mix up the
if condition with the value in the write.

	clk_alpha_pll_write_config(regmap, PLL_L_VAL(pll), config->l);

static void clk_alpha_pll_write_config(struct regmap *regmap,
				       unsigned int reg,
				       unsigned int val) {
	if (val)
		regmap_write(regmap, reg, val);
}

and how are we so lucky that zero isn't a value that we may need to
write?

> +
> +       if (config->alpha)
> +               regmap_write(regmap, PLL_ALPHA_VAL(pll), config->alpha);
> +
> +       if (config->user_ctl_val)
> +               regmap_write(regmap, PLL_USER_CTL(pll), config->user_ctl_val);
> +
> +       if (config->config_ctl_val)
> +               regmap_write(regmap, PLL_CONFIG_CTL(pll),
> +                                               config->config_ctl_val);
> +
> +       if (config->config_ctl_hi_val)
> +               regmap_write(regmap, PLL_CONFIG_CTL_U(pll),
> +                                               config->config_ctl_hi_val);
> +
> +       if (config->test_ctl_val)
> +               regmap_write(regmap, PLL_TEST_CTL(pll),
> +                                               config->test_ctl_val);
> +
> +       if (config->test_ctl_hi_val)
> +               regmap_write(regmap,  PLL_TEST_CTL_U(pll),
> +                                               config->test_ctl_hi_val);
> +}
> +EXPORT_SYMBOL_GPL(clk_agera_pll_configure);
> +
> +static int clk_alpha_pll_agera_set_rate(struct clk_hw *hw, unsigned long rate,
> +                                                       unsigned long prate)
> +{
> +       struct clk_alpha_pll *pll = to_clk_alpha_pll(hw);
> +       u32 l, alpha_width = pll_alpha_width(pll);
> +       unsigned long rrate, max = rate + PLL_RATE_MARGIN;
> +       u64 a;
> +
> +       rrate = alpha_pll_round_rate(rate, prate, &l, &a, alpha_width);
> +
> +       /*
> +        * Due to limited number of bits for fractional rate programming, the
> +        * rounded up rate could be marginally higher than the requested rate.
> +        */
> +       if (rrate > (rate + PLL_RATE_MARGIN) || rrate < rate) {
> +               pr_err("%s: Rounded rate %lu not within range [%lu, %lu)\n",
> +                      clk_hw_get_name(hw), rrate, rate, max);
> +               return -EINVAL;
> +       }

Can this be extracted into a helper function?

> +
> +       /* change L_VAL without having to go through the power on sequence */
> +       regmap_write(pll->clkr.regmap, PLL_L_VAL(pll), l);
> +       regmap_write(pll->clkr.regmap, PLL_ALPHA_VAL(pll), a);
> +
> +       if (clk_hw_is_enabled(hw))
> +               return wait_for_pll_enable_lock(pll);
> +
> +       return 0;
> +}
> +