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Message-ID: <82072c2b-8483-6fb6-a9d1-c9882825c9cb@linaro.org>
Date:   Sat, 27 May 2023 18:11:16 +0200
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To:     Christian Marangi <ansuelsmth@gmail.com>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>, linux-arm-msm@vger.kernel.org,
        linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20230427150717.20860-1-ansuelsmth@gmail.com>
 <20230427150717.20860-3-ansuelsmth@gmail.com>
From:   Konrad Dybcio <konrad.dybcio@linaro.org>
Subject: Re: [PATCH v4 2/3] clk: qcom: clk-rcg2: add support for rcg2 freq
 multi ops
In-Reply-To: <20230427150717.20860-3-ansuelsmth@gmail.com>
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On 27.04.2023 17:07, 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.
> 
> Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
> ---
>  drivers/clk/qcom/clk-rcg.h  |   1 +
>  drivers/clk/qcom/clk-rcg2.c | 152 ++++++++++++++++++++++++++++++++++++
>  drivers/clk/qcom/common.c   |  18 +++++
>  drivers/clk/qcom/common.h   |   2 +
>  4 files changed, 173 insertions(+)
> 
> diff --git a/drivers/clk/qcom/clk-rcg.h b/drivers/clk/qcom/clk-rcg.h
> index dc85b46b0d79..f8ec989ed3d9 100644
> --- a/drivers/clk/qcom/clk-rcg.h
> +++ b/drivers/clk/qcom/clk-rcg.h
> @@ -188,6 +188,7 @@ struct clk_rcg2_gfx3d {
>  
>  extern const struct clk_ops clk_rcg2_ops;
>  extern const struct clk_ops clk_rcg2_floor_ops;
> +extern const struct clk_ops clk_rcg2_fm_ops;
>  extern const struct clk_ops clk_rcg2_mux_closest_ops;
>  extern const struct clk_ops clk_edp_pixel_ops;
>  extern const struct clk_ops clk_byte_ops;
> diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
> index 76551534f10d..4f2fe012ef5f 100644
> --- a/drivers/clk/qcom/clk-rcg2.c
> +++ b/drivers/clk/qcom/clk-rcg2.c
> @@ -266,6 +266,104 @@ 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 best_rate = 0, parent_rate, rate;
> +	const struct freq_conf *conf, *best_conf;
> +	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> +	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;
> +		}
> +
> +		if (abs(req_rate - rate) < abs(best_rate - rate)) {
Shouldn't this be:

if (abs(req_rate - rate) < abs(best_rate - req_rate)

?

this way it'd say

"if this iteration's rate is closer to the requested one than the
best one we've found yet, it's better"

> +			best_rate = rate;
> +			best_conf = conf;
> +		}
> +	}
> +
> +	/*
> +	 * Very unlikely.
> +	 * Force the first conf if we can't find a correct config.
> +	 */
> +	if (unlikely(i == f->num_confs))
> +		best_conf = f->confs;
Is that a supported scenario or would it be a device driver / clock
driver error?

> +
> +	return best_conf;
> +}
> +
> +static int _freq_tbl_fm_determine_rate(struct clk_hw *hw, const struct freq_multi_tbl *f,
> +				       struct clk_rate_request *req)
> +{
> +	unsigned long clk_flags, rate = req->rate;
> +	const struct freq_conf *conf;
> +	struct clk_hw *p;
> +	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
swap lines 2, 3, 4 to 4, 2, 3 and you'll get a revers-Christmas-tree!

Konrad