// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2024 SpacemiT Technology Co. Ltd
 * Copyright (c) 2024-2025 Haylen Chu <heylenay@4d2.org>
 *
 * DDN stands for "Divider Denominator Numerator", it's M/N clock with a
 * constant x2 factor. This clock hardware follows the equation below,
 *
 *            numerator       Fin
 *      2 * ------------- = -------
 *           denominator      Fout
 *
 * Thus, Fout could be calculated with,
 *
 *              Fin     denominator
 *      Fout = ----- * -------------
 *               2       numerator
 */

#include <linux/clk-provider.h>
#include <linux/rational.h>

#include "ccu_ddn.h"

static unsigned long ccu_ddn_calc_rate(unsigned long prate, unsigned long num,
                                       unsigned long den, unsigned int pre_div)
{
        return prate * den / pre_div / num;
}

static unsigned long ccu_ddn_calc_best_rate(struct ccu_ddn *ddn,
                                            unsigned long rate, unsigned long prate,
                                            unsigned long *num, unsigned long *den)
{
        rational_best_approximation(rate, prate / ddn->pre_div,
                                    ddn->den_mask >> ddn->den_shift,
                                    ddn->num_mask >> ddn->num_shift,
                                    den, num);
        return ccu_ddn_calc_rate(prate, *num, *den, ddn->pre_div);
}

static int ccu_ddn_determine_rate(struct clk_hw *hw,
                                  struct clk_rate_request *req)
{
        struct ccu_ddn *ddn = hw_to_ccu_ddn(hw);
        unsigned long num, den;

        req->rate = ccu_ddn_calc_best_rate(ddn, req->rate,
                                           req->best_parent_rate, &num, &den);

        return 0;
}

static unsigned long ccu_ddn_recalc_rate(struct clk_hw *hw, unsigned long prate)
{
        struct ccu_ddn *ddn = hw_to_ccu_ddn(hw);
        unsigned int val, num, den;

        val = ccu_read(&ddn->common, ctrl);

        num = (val & ddn->num_mask) >> ddn->num_shift;
        den = (val & ddn->den_mask) >> ddn->den_shift;

        return ccu_ddn_calc_rate(prate, num, den, ddn->pre_div);
}

static int ccu_ddn_set_rate(struct clk_hw *hw, unsigned long rate,
                            unsigned long prate)
{
        struct ccu_ddn *ddn = hw_to_ccu_ddn(hw);
        unsigned long num, den;

        ccu_ddn_calc_best_rate(ddn, rate, prate, &num, &den);

        ccu_update(&ddn->common, ctrl,
                   ddn->num_mask | ddn->den_mask,
                   (num << ddn->num_shift) | (den << ddn->den_shift));

        return 0;
}

const struct clk_ops spacemit_ccu_ddn_ops = {
        .recalc_rate    = ccu_ddn_recalc_rate,
        .determine_rate = ccu_ddn_determine_rate,
        .set_rate       = ccu_ddn_set_rate,
};
EXPORT_SYMBOL_NS_GPL(spacemit_ccu_ddn_ops, "CLK_SPACEMIT");