drivers/clk/clk-si544.c

root/drivers/clk/clk-si544.c
// SPDX-License-Identifier: GPL-2.0
/*
 * Driver for Silicon Labs Si544 Programmable Oscillator
 * Copyright (C) 2018 Topic Embedded Products
 * Author: Mike Looijmans <mike.looijmans@topic.nl>
 */

#include <linux/clk-provider.h>
#include <linux/delay.h>
#include <linux/math64.h>
#include <linux/module.h>
#include <linux/i2c.h>
#include <linux/regmap.h>
#include <linux/slab.h>

/* I2C registers (decimal as in datasheet) */
#define SI544_REG_CONTROL       7
#define SI544_REG_OE_STATE      17
#define SI544_REG_HS_DIV        23
#define SI544_REG_LS_HS_DIV     24
#define SI544_REG_FBDIV0        26
#define SI544_REG_FBDIV8        27
#define SI544_REG_FBDIV16       28
#define SI544_REG_FBDIV24       29
#define SI544_REG_FBDIV32       30
#define SI544_REG_FBDIV40       31
#define SI544_REG_FCAL_OVR      69
#define SI544_REG_ADPLL_DELTA_M0        231
#define SI544_REG_ADPLL_DELTA_M8        232
#define SI544_REG_ADPLL_DELTA_M16       233
#define SI544_REG_PAGE_SELECT   255

/* Register values */
#define SI544_CONTROL_RESET     BIT(7)
#define SI544_CONTROL_MS_ICAL2  BIT(3)

#define SI544_OE_STATE_ODC_OE   BIT(0)

/* Max freq depends on speed grade */
#define SI544_MIN_FREQ      200000U

/* Si544 Internal oscillator runs at 55.05 MHz */
#define FXO               55050000U

/* VCO range is 10.8 .. 12.1 GHz, max depends on speed grade */
#define FVCO_MIN       10800000000ULL

#define HS_DIV_MAX      2046
#define HS_DIV_MAX_ODD  33

/* Lowest frequency synthesizeable using only the HS divider */
#define MIN_HSDIV_FREQ  (FVCO_MIN / HS_DIV_MAX)

/* Range and interpretation of the adjustment value */
#define DELTA_M_MAX     8161512
#define DELTA_M_FRAC_NUM        19
#define DELTA_M_FRAC_DEN        20000

struct clk_si544 {
        struct clk_hw hw;
        struct regmap *regmap;
        struct i2c_client *i2c_client;
        unsigned long  max_freq;
};
#define to_clk_si544(_hw)       container_of(_hw, struct clk_si544, hw)

/**
 * struct clk_si544_muldiv - Multiplier/divider settings
 * @fb_div_frac:        integer part of feedback divider (32 bits)
 * @fb_div_int:         fractional part of feedback divider (11 bits)
 * @hs_div:             1st divider, 5..2046, must be even when >33
 * @ls_div_bits:        2nd divider, as 2^x, range 0..5
 *                      If ls_div_bits is non-zero, hs_div must be even
 * @delta_m:            Frequency shift for small -950..+950 ppm changes, 24 bit
 */
struct clk_si544_muldiv {
        u32 fb_div_frac;
        u16 fb_div_int;
        u16 hs_div;
        u8 ls_div_bits;
        s32 delta_m;
};

/* Enables or disables the output driver */
static int si544_enable_output(struct clk_si544 *data, bool enable)
{
        return regmap_update_bits(data->regmap, SI544_REG_OE_STATE,
                SI544_OE_STATE_ODC_OE, enable ? SI544_OE_STATE_ODC_OE : 0);
}

static int si544_prepare(struct clk_hw *hw)
{
        struct clk_si544 *data = to_clk_si544(hw);

        return si544_enable_output(data, true);
}

static void si544_unprepare(struct clk_hw *hw)
{
        struct clk_si544 *data = to_clk_si544(hw);

        si544_enable_output(data, false);
}

static int si544_is_prepared(struct clk_hw *hw)
{
        struct clk_si544 *data = to_clk_si544(hw);
        unsigned int val;
        int err;

        err = regmap_read(data->regmap, SI544_REG_OE_STATE, &val);
        if (err < 0)
                return err;

        return !!(val & SI544_OE_STATE_ODC_OE);
}

/* Retrieve clock multiplier and dividers from hardware */
static int si544_get_muldiv(struct clk_si544 *data,
        struct clk_si544_muldiv *settings)
{
        int err;
        u8 reg[6];

        err = regmap_bulk_read(data->regmap, SI544_REG_HS_DIV, reg, 2);
        if (err)
                return err;

        settings->ls_div_bits = (reg[1] >> 4) & 0x07;
        settings->hs_div = (reg[1] & 0x07) << 8 | reg[0];

        err = regmap_bulk_read(data->regmap, SI544_REG_FBDIV0, reg, 6);
        if (err)
                return err;

        settings->fb_div_int = reg[4] | (reg[5] & 0x07) << 8;
        settings->fb_div_frac = reg[0] | reg[1] << 8 | reg[2] << 16 |
                                reg[3] << 24;

        err = regmap_bulk_read(data->regmap, SI544_REG_ADPLL_DELTA_M0, reg, 3);
        if (err)
                return err;

        /* Interpret as 24-bit signed number */
        settings->delta_m = reg[0] << 8 | reg[1] << 16 | reg[2] << 24;
        settings->delta_m >>= 8;

        return 0;
}

static int si544_set_delta_m(struct clk_si544 *data, s32 delta_m)
{
        u8 reg[3];

        reg[0] = delta_m;
        reg[1] = delta_m >> 8;
        reg[2] = delta_m >> 16;

        return regmap_bulk_write(data->regmap, SI544_REG_ADPLL_DELTA_M0,
                                 reg, 3);
}

static int si544_set_muldiv(struct clk_si544 *data,
        struct clk_si544_muldiv *settings)
{
        int err;
        u8 reg[6];

        reg[0] = settings->hs_div;
        reg[1] = settings->hs_div >> 8 | settings->ls_div_bits << 4;

        err = regmap_bulk_write(data->regmap, SI544_REG_HS_DIV, reg, 2);
        if (err < 0)
                return err;

        reg[0] = settings->fb_div_frac;
        reg[1] = settings->fb_div_frac >> 8;
        reg[2] = settings->fb_div_frac >> 16;
        reg[3] = settings->fb_div_frac >> 24;
        reg[4] = settings->fb_div_int;
        reg[5] = settings->fb_div_int >> 8;

        /*
         * Writing to SI544_REG_FBDIV40 triggers the clock change, so that
         * must be written last
         */
        return regmap_bulk_write(data->regmap, SI544_REG_FBDIV0, reg, 6);
}

static bool is_valid_frequency(const struct clk_si544 *data,
        unsigned long frequency)
{
        if (frequency < SI544_MIN_FREQ)
                return false;

        return frequency <= data->max_freq;
}

/* Calculate divider settings for a given frequency */
static int si544_calc_muldiv(struct clk_si544_muldiv *settings,
        unsigned long frequency)
{
        u64 vco;
        u32 ls_freq;
        u32 tmp;
        u8 res;

        /* Determine the minimum value of LS_DIV and resulting target freq. */
        ls_freq = frequency;
        settings->ls_div_bits = 0;

        if (frequency >= MIN_HSDIV_FREQ) {
                settings->ls_div_bits = 0;
        } else {
                res = 1;
                tmp = 2 * HS_DIV_MAX;
                while (tmp <= (HS_DIV_MAX * 32)) {
                        if (((u64)frequency * tmp) >= FVCO_MIN)
                                break;
                        ++res;
                        tmp <<= 1;
                }
                settings->ls_div_bits = res;
                ls_freq = frequency << res;
        }

        /* Determine minimum HS_DIV by rounding up */
        vco = FVCO_MIN + ls_freq - 1;
        do_div(vco, ls_freq);
        settings->hs_div = vco;

        /* round up to even number when required */
        if ((settings->hs_div & 1) &&
            (settings->hs_div > HS_DIV_MAX_ODD || settings->ls_div_bits))
                ++settings->hs_div;

        /* Calculate VCO frequency (in 10..12GHz range) */
        vco = (u64)ls_freq * settings->hs_div;

        /* Calculate the integer part of the feedback divider */
        tmp = do_div(vco, FXO);
        settings->fb_div_int = vco;

        /* And the fractional bits using the remainder */
        vco = (u64)tmp << 32;
        vco += FXO / 2; /* Round to nearest multiple */
        do_div(vco, FXO);
        settings->fb_div_frac = vco;

        /* Reset the frequency adjustment */
        settings->delta_m = 0;

        return 0;
}

/* Calculate resulting frequency given the register settings */
static unsigned long si544_calc_center_rate(
                const struct clk_si544_muldiv *settings)
{
        u32 d = settings->hs_div * BIT(settings->ls_div_bits);
        u64 vco;

        /* Calculate VCO from the fractional part */
        vco = (u64)settings->fb_div_frac * FXO;
        vco += (FXO / 2);
        vco >>= 32;

        /* Add the integer part of the VCO frequency */
        vco += (u64)settings->fb_div_int * FXO;

        /* Apply divider to obtain the generated frequency */
        do_div(vco, d);

        return vco;
}

static unsigned long si544_calc_rate(const struct clk_si544_muldiv *settings)
{
        unsigned long rate = si544_calc_center_rate(settings);
        s64 delta = (s64)rate * (DELTA_M_FRAC_NUM * settings->delta_m);

        /*
         * The clock adjustment is much smaller than 1 Hz, round to the
         * nearest multiple. Apparently div64_s64 rounds towards zero, hence
         * check the sign and adjust into the proper direction.
         */
        if (settings->delta_m < 0)
                delta -= ((s64)DELTA_M_MAX * DELTA_M_FRAC_DEN) / 2;
        else
                delta += ((s64)DELTA_M_MAX * DELTA_M_FRAC_DEN) / 2;
        delta = div64_s64(delta, ((s64)DELTA_M_MAX * DELTA_M_FRAC_DEN));

        return rate + delta;
}

static unsigned long si544_recalc_rate(struct clk_hw *hw,
                unsigned long parent_rate)
{
        struct clk_si544 *data = to_clk_si544(hw);
        struct clk_si544_muldiv settings;
        int err;

        err = si544_get_muldiv(data, &settings);
        if (err)
                return 0;

        return si544_calc_rate(&settings);
}

static int si544_determine_rate(struct clk_hw *hw,
                                struct clk_rate_request *req)
{
        struct clk_si544 *data = to_clk_si544(hw);

        if (!is_valid_frequency(data, req->rate))
                return -EINVAL;

        /* The accuracy is less than 1 Hz, so any rate is possible */
        return 0;
}

/* Calculates the maximum "small" change, 950 * rate / 1000000 */
static unsigned long si544_max_delta(unsigned long rate)
{
        u64 num = rate;

        num *= DELTA_M_FRAC_NUM;
        do_div(num, DELTA_M_FRAC_DEN);

        return num;
}

static s32 si544_calc_delta(s32 delta, s32 max_delta)
{
        s64 n = (s64)delta * DELTA_M_MAX;

        return div_s64(n, max_delta);
}

static int si544_set_rate(struct clk_hw *hw, unsigned long rate,
                unsigned long parent_rate)
{
        struct clk_si544 *data = to_clk_si544(hw);
        struct clk_si544_muldiv settings;
        unsigned long center;
        long max_delta;
        long delta;
        unsigned int old_oe_state;
        int err;

        if (!is_valid_frequency(data, rate))
                return -EINVAL;

        /* Try using the frequency adjustment feature for a <= 950ppm change */
        err = si544_get_muldiv(data, &settings);
        if (err)
                return err;

        center = si544_calc_center_rate(&settings);
        max_delta = si544_max_delta(center);
        delta = rate - center;

        if (abs(delta) <= max_delta)
                return si544_set_delta_m(data,
                                         si544_calc_delta(delta, max_delta));

        /* Too big for the delta adjustment, need to reprogram */
        err = si544_calc_muldiv(&settings, rate);
        if (err)
                return err;

        err = regmap_read(data->regmap, SI544_REG_OE_STATE, &old_oe_state);
        if (err)
                return err;

        si544_enable_output(data, false);

        /* Allow FCAL for this frequency update */
        err = regmap_write(data->regmap, SI544_REG_FCAL_OVR, 0);
        if (err < 0)
                return err;

        err = si544_set_delta_m(data, settings.delta_m);
        if (err < 0)
                return err;

        err = si544_set_muldiv(data, &settings);
        if (err < 0)
                return err; /* Undefined state now, best to leave disabled */

        /* Trigger calibration */
        err = regmap_write(data->regmap, SI544_REG_CONTROL,
                           SI544_CONTROL_MS_ICAL2);
        if (err < 0)
                return err;

        /* Applying a new frequency can take up to 10ms */
        usleep_range(10000, 12000);

        if (old_oe_state & SI544_OE_STATE_ODC_OE)
                si544_enable_output(data, true);

        return err;
}

static const struct clk_ops si544_clk_ops = {
        .prepare = si544_prepare,
        .unprepare = si544_unprepare,
        .is_prepared = si544_is_prepared,
        .recalc_rate = si544_recalc_rate,
        .determine_rate = si544_determine_rate,
        .set_rate = si544_set_rate,
};

static bool si544_regmap_is_volatile(struct device *dev, unsigned int reg)
{
        switch (reg) {
        case SI544_REG_CONTROL:
        case SI544_REG_FCAL_OVR:
                return true;
        default:
                return false;
        }
}

static const struct regmap_config si544_regmap_config = {
        .reg_bits = 8,
        .val_bits = 8,
        .cache_type = REGCACHE_MAPLE,
        .max_register = SI544_REG_PAGE_SELECT,
        .volatile_reg = si544_regmap_is_volatile,
};

static int si544_probe(struct i2c_client *client)
{
        struct clk_si544 *data;
        struct clk_init_data init;
        int err;

        data = devm_kzalloc(&client->dev, sizeof(*data), GFP_KERNEL);
        if (!data)
                return -ENOMEM;

        init.ops = &si544_clk_ops;
        init.flags = 0;
        init.num_parents = 0;
        data->hw.init = &init;
        data->i2c_client = client;
        data->max_freq = (uintptr_t)i2c_get_match_data(client);

        if (of_property_read_string(client->dev.of_node, "clock-output-names",
                        &init.name))
                init.name = client->dev.of_node->name;

        data->regmap = devm_regmap_init_i2c(client, &si544_regmap_config);
        if (IS_ERR(data->regmap))
                return PTR_ERR(data->regmap);

        i2c_set_clientdata(client, data);

        /* Select page 0, just to be sure, there appear to be no more */
        err = regmap_write(data->regmap, SI544_REG_PAGE_SELECT, 0);
        if (err < 0)
                return err;

        err = devm_clk_hw_register(&client->dev, &data->hw);
        if (err) {
                dev_err(&client->dev, "clock registration failed\n");
                return err;
        }
        err = devm_of_clk_add_hw_provider(&client->dev, of_clk_hw_simple_get,
                                          &data->hw);
        if (err) {
                dev_err(&client->dev, "unable to add clk provider\n");
                return err;
        }

        return 0;
}

static const struct i2c_device_id si544_id[] = {
        { "si544a", 1500000000 },
        { "si544b", 800000000 },
        { "si544c", 350000000 },
        { }
};
MODULE_DEVICE_TABLE(i2c, si544_id);

static const struct of_device_id clk_si544_of_match[] = {
        { .compatible = "silabs,si544a", .data = (void *)1500000000 },
        { .compatible = "silabs,si544b", .data = (void *)800000000 },
        { .compatible = "silabs,si544c", .data = (void *)350000000 },
        { }
};
MODULE_DEVICE_TABLE(of, clk_si544_of_match);

static struct i2c_driver si544_driver = {
        .driver = {
                .name = "si544",
                .of_match_table = clk_si544_of_match,
        },
        .probe          = si544_probe,
        .id_table       = si544_id,
};
module_i2c_driver(si544_driver);

MODULE_AUTHOR("Mike Looijmans <mike.looijmans@topic.nl>");
MODULE_DESCRIPTION("Si544 driver");
MODULE_LICENSE("GPL");
Linux
