linux-kernel - Re: [PATCH v2] clk: qcom: clk-rcg2: Add support for duty-cycle for RCG

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Message-ID: <161567639878.1478170.18101287599042992816@swboyd.mtv.corp.google.com>
Date:   Sat, 13 Mar 2021 14:59:58 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Taniya Das <tdas@...eaurora.org>
Cc:     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,
        Taniya Das <tdas@...eaurora.org>
Subject: Re: [PATCH v2] clk: qcom: clk-rcg2: Add support for duty-cycle for RCG

Quoting Taniya Das (2021-03-11 04:51:32)
> The root clock generators with MND divider has the capability to support
> change in duty-cycle by updating the 'D'. Add the clock ops which would
> check all the boundary conditions and enable setting the desired duty-cycle
> as per the consumer.
> 
> Signed-off-by: Taniya Das <tdas@...eaurora.org>
> ---
>  drivers/clk/qcom/clk-rcg2.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 
> diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
> index 42f13a2..aac6893 100644
> --- a/drivers/clk/qcom/clk-rcg2.c
> +++ b/drivers/clk/qcom/clk-rcg2.c
> @@ -357,6 +357,46 @@ static int clk_rcg2_set_floor_rate_and_parent(struct clk_hw *hw,
>         return __clk_rcg2_set_rate(hw, rate, FLOOR);
>  }
> 
> +static int clk_rcg2_set_duty_cycle(struct clk_hw *hw, struct clk_duty *duty)
> +{
> +       struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> +       u32 notn_m_val, n_val, m_val, d_val, not2d_val, mask, duty_per;
> +       int ret;
> +
> +       if (!rcg->mnd_width)
> +               return 0;

Shouldn't we fail this call if the duty cycle can't be changed? Or have
another set of clk ops that doesn't support this clk op if the mnd 
isn't present.

> +
> +       mask = BIT(rcg->mnd_width) - 1;
> +
> +       regmap_read(rcg->clkr.regmap, RCG_N_OFFSET(rcg), &notn_m_val);
> +       regmap_read(rcg->clkr.regmap, RCG_M_OFFSET(rcg), &m_val);
> +
> +       n_val = (~(notn_m_val) + m_val) & mask;
> +
> +       duty_per = (duty->num * 100) / duty->den;
> +
> +       /* Calculate 2d value */
> +       d_val = DIV_ROUND_CLOSEST(n_val * duty_per * 2, 100);
> +
> +        /* Check BIT WIDTHS OF 2d. If D is too big reduce Duty cycle. */

Why is BIT WIDTHS capitalized? And Duty?

> +       if (d_val > mask)
> +               d_val = mask;
> +
> +       if ((d_val / 2) > (n_val - m_val))
> +               d_val = (n_val - m_val) * 2;
> +       else if ((d_val / 2) < (m_val / 2))
> +               d_val = m_val;
> +
> +       not2d_val = ~d_val & mask;
> +
> +       ret = regmap_update_bits(rcg->clkr.regmap, RCG_D_OFFSET(rcg), mask,
> +                                not2d_val);
> +       if (ret)
> +               return ret;
> +
> +       return update_config(rcg);
> +}
> +
>  const struct clk_ops clk_rcg2_ops = {
>         .is_enabled = clk_rcg2_is_enabled,
>         .get_parent = clk_rcg2_get_parent,
> @@ -365,6 +405,7 @@ const struct clk_ops clk_rcg2_ops = {
>         .determine_rate = clk_rcg2_determine_rate,
>         .set_rate = clk_rcg2_set_rate,
>         .set_rate_and_parent = clk_rcg2_set_rate_and_parent,
> +       .set_duty_cycle = clk_rcg2_set_duty_cycle,

Can you also implement get_duty_cycle?

>  };
>  EXPORT_SYMBOL_GPL(clk_rcg2_ops);
>