linux-kernel - Re: [PATCH v5 2/3] clk: qcom: clk-rcg2: add support for rcg2 freq multi ops

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Date:   Thu, 13 Jul 2023 06:32:01 +0100
From:   Simon Horman <horms@...nel.org>
To:     Christian Marangi <ansuelsmth@...il.com>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/3] clk: qcom: clk-rcg2: add support for rcg2 freq
 multi ops

On Thu, Jun 01, 2023 at 12:26:53AM +0200, Christian Marangi wrote:
> Some RCG frequency can be reached by multiple configuration.
> 
> Add clk_rcg2_fm_ops ops to support these special RCG configurations.
> 
> These alternative ops will select the frequency using a CEIL policy.
> 
> When the correct frequency is found, the correct config is selected by
> calculating the final rate (by checking the defined parent and values
> in the config that is being checked) and deciding based on the one that
> is less different than the requested one.
> 
> These check are skipped if there is just on config for the requested
> freq.
> 
> qcom_find_freq_multi is added to search the freq with the new struct
> freq_multi_tbl.
> __clk_rcg2_select_conf is used to select the correct conf by simulating
> the final clock.
> If a conf can't be found due to parent not reachable, a WARN is printed
> and -EINVAL is returned.
> 
> Signed-off-by: Christian Marangi <ansuelsmth@...il.com>

...

> diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
> index 76551534f10d..9a139fc8bbfa 100644
> --- a/drivers/clk/qcom/clk-rcg2.c
> +++ b/drivers/clk/qcom/clk-rcg2.c
> @@ -266,6 +266,112 @@ static int _freq_tbl_determine_rate(struct clk_hw *hw, const struct freq_tbl *f,
>  	return 0;
>  }
>  
> +static const struct freq_conf *
> +__clk_rcg2_select_conf(struct clk_hw *hw, const struct freq_multi_tbl *f,
> +		       unsigned long req_rate)
> +{
> +	unsigned long rate_diff, best_rate_diff = ULONG_MAX;
> +	const struct freq_conf *conf, *best_conf;
> +	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> +	const char *name = clk_hw_get_name(hw);
> +	unsigned long parent_rate, rate;
> +	struct clk_hw *p;
> +	int index, i;
> +
> +	/* Exit early if only one config is defined */
> +	if (f->num_confs == 1)
> +		return f->confs;
> +
> +	/* Search in each provided config the one that is near the wanted rate */
> +	for (i = 0, conf = f->confs; i < f->num_confs; i++, conf++) {
> +		index = qcom_find_src_index(hw, rcg->parent_map, conf->src);
> +		if (index < 0)
> +			continue;
> +
> +		p = clk_hw_get_parent_by_index(hw, index);
> +		if (!p)
> +			continue;
> +
> +		parent_rate =  clk_hw_get_rate(p);
> +		rate = calc_rate(parent_rate, conf->n, conf->m, conf->n, conf->pre_div);
> +
> +		if (rate == req_rate) {
> +			best_conf = conf;
> +			break;
> +		}
> +
> +		rate_diff = abs(req_rate - rate);
> +		if (rate_diff < best_rate_diff) {
> +			best_rate_diff = rate_diff;
> +			best_conf = conf;
> +		}
> +	}
> +
> +	/*
> +	 * Very unlikely. Warn if we couldn't find a correct config
> +	 * due to parent not present.
> +	 */
> +	if (unlikely(i == f->num_confs)) {
> +		WARN(1, "%s: can't find a configuration for rate %lu.",
> +		     name, req_rate);
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	return best_conf;

Hi Christian,

It's unclear to me if this can actually occur,
but Sparse warns that best_conf may be uninitialised here.

> +}

...