clk-frac-synth.c

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/*
 * Copyright (C) 2012 ST Microelectronics
 * Viresh Kumar <[email protected]>
 *
 * This file is licensed under the terms of the GNU General Public
 * License version 2. This program is licensed "as is" without any
 * warranty of any kind, whether express or implied.
 *
 * Fractional Synthesizer clock implementation
 */

#define pr_fmt(fmt) "clk-frac-synth: " fmt

#include <linux/clk-provider.h>
#include <linux/slab.h>
#include <linux/io.h>
#include <linux/err.h>
#include "clk.h"

#define DIV_FACTOR_MASK     0x1FFFF

/*
 * DOC: Fractional Synthesizer clock
 *
 * Fout from synthesizer can be given from below equation:
 *
 * Fout= Fin/2*div (division factor)
 * div is 17 bits:-
 *  0-13 (fractional part)
 *  14-16 (integer part)
 *  div is (16-14 bits).(13-0 bits) (in binary)
 *
 *  Fout = Fin/(2 * div)
 *  Fout = ((Fin / 10000)/(2 * div)) * 10000
 *  Fout = (2^14 * (Fin / 10000)/(2^14 * (2 * div))) * 10000
 *  Fout = (((Fin / 10000) << 14)/(2 * (div << 14))) * 10000
 *
 * div << 14 simply 17 bit value written at register.
 * Max error due to scaling down by 10000 is 10 KHz
 */

#define to_clk_frac(_hw) container_of(_hw, struct clk_frac, hw)

static unsigned long frac_calc_rate(struct clk_hw *hw, unsigned long prate,
        int index)
{
    struct clk_frac *frac = to_clk_frac(hw);
    struct frac_rate_tbl *rtbl = frac->rtbl;

    prate /= 10000;
    prate <<= 14;
    prate /= (2 * rtbl[index].div);
    prate *= 10000;

    return prate;
}

static long clk_frac_round_rate(struct clk_hw *hw, unsigned long drate,
        unsigned long *prate)
{
    struct clk_frac *frac = to_clk_frac(hw);
    int unused;

    return clk_round_rate_index(hw, drate, *prate, frac_calc_rate,
            frac->rtbl_cnt, &unused);
}

static unsigned long clk_frac_recalc_rate(struct clk_hw *hw,
        unsigned long parent_rate)
{
    struct clk_frac *frac = to_clk_frac(hw);
    unsigned long flags = 0;
    unsigned int div = 1, val;

    if (frac->lock)
        spin_lock_irqsave(frac->lock, flags);

    val = readl_relaxed(frac->reg);

    if (frac->lock)
        spin_unlock_irqrestore(frac->lock, flags);

    div = val & DIV_FACTOR_MASK;

    if (!div)
        return 0;

    parent_rate = parent_rate / 10000;

    parent_rate = (parent_rate << 14) / (2 * div);
    return parent_rate * 10000;
}

/* Configures new clock rate of frac */
static int clk_frac_set_rate(struct clk_hw *hw, unsigned long drate,
                unsigned long prate)
{
    struct clk_frac *frac = to_clk_frac(hw);
    struct frac_rate_tbl *rtbl = frac->rtbl;
    unsigned long flags = 0, val;
    int i;

    clk_round_rate_index(hw, drate, prate, frac_calc_rate, frac->rtbl_cnt,
            &i);

    if (frac->lock)
        spin_lock_irqsave(frac->lock, flags);

    val = readl_relaxed(frac->reg) & ~DIV_FACTOR_MASK;
    val |= rtbl[i].div & DIV_FACTOR_MASK;
    writel_relaxed(val, frac->reg);

    if (frac->lock)
        spin_unlock_irqrestore(frac->lock, flags);

    return 0;
}

struct clk_ops clk_frac_ops = {
    .recalc_rate = clk_frac_recalc_rate,
    .round_rate = clk_frac_round_rate,
    .set_rate = clk_frac_set_rate,
};

struct clk *clk_register_frac(const char *name, const char *parent_name,
        unsigned long flags, void __iomem *reg,
        struct frac_rate_tbl *rtbl, u8 rtbl_cnt, spinlock_t *lock)
{
    struct clk_init_data init;
    struct clk_frac *frac;
    struct clk *clk;

    if (!name || !parent_name || !reg || !rtbl || !rtbl_cnt) {
        pr_err("Invalid arguments passed");
        return ERR_PTR(-EINVAL);
    }

    frac = kzalloc(sizeof(*frac), GFP_KERNEL);
    if (!frac) {
        pr_err("could not allocate frac clk\n");
        return ERR_PTR(-ENOMEM);
    }

    /* struct clk_frac assignments */
    frac->reg = reg;
    frac->rtbl = rtbl;
    frac->rtbl_cnt = rtbl_cnt;
    frac->lock = lock;
    frac->hw.init = &init;

    init.name = name;
    init.ops = &clk_frac_ops;
    init.flags = flags;
    init.parent_names = &parent_name;
    init.num_parents = 1;

    clk = clk_register(NULL, &frac->hw);
    if (!IS_ERR_OR_NULL(clk))
        return clk;

    pr_err("clk register failed\n");
    kfree(frac);

    return NULL;
}