linux-kernel - Re: [PATCH] clk: tegra: Return the exact clock rate from clk_round

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Message-ID: <20180924080803.GF7636@tbergstrom-lnx.Nvidia.com>
Date:   Mon, 24 Sep 2018 11:08:03 +0300
From:   Peter De Schrijver <pdeschrijver@...dia.com>
To:     ryang <decatf@...il.com>
CC:     Prashant Gaikwad <pgaikwad@...dia.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        <linux-clk@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: tegra: Return the exact clock rate from
 clk_round_rate

On Fri, Sep 21, 2018 at 06:01:49PM -0400, ryang wrote:
> The current behavior is that clk_round_rate would return the same clock
> rate passed to it for valid PLL configurations. This change will return
> the exact rate the PLL will provide in accordance with clk API.
> 
> Signed-off-by: ryang <decatf@...il.com>
> ---
>  drivers/clk/tegra/clk-pll.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/tegra/clk-pll.c b/drivers/clk/tegra/clk-pll.c
> index 17a058c3bbc1..36014a6ec42e 100644
> --- a/drivers/clk/tegra/clk-pll.c
> +++ b/drivers/clk/tegra/clk-pll.c
> @@ -595,7 +595,12 @@ static int _calc_rate(struct clk_hw *hw, struct tegra_clk_pll_freq_table *cfg,
>  		return -EINVAL;
>  	}
>  
> -	cfg->output_rate >>= p_div;
> +	if (cfg->m == 0) {
> +		cfg->output_rate = 0;

I think a WARN_ON() is appropriate here. the input divider should never be 0.

Peter.

> +	} else {
> +		cfg->output_rate = cfg->n * DIV_ROUND_UP(parent_rate, cfg->m);
> +		cfg->output_rate >>= p_div;
> +	}
>  
>  	if (pll->params->pdiv_tohw) {
>  		ret = _p_div_to_hw(hw, 1 << p_div);
> -- 
> 2.17.1
>