/*
   * Driver for Silicon Labs Si514 Programmable Oscillator
   *
   * Copyright (C) 2015 Topic Embedded Products
   *
   * Author: Mike Looijmans <mike.looijmans@topic.nl>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   */
  
  #include <linux/clk-provider.h>
  #include <linux/delay.h>
  #include <linux/module.h>
  #include <linux/i2c.h>
  #include <linux/regmap.h>
  #include <linux/slab.h>
  
  /* I2C registers */
  #define SI514_REG_LP		0
  #define SI514_REG_M_FRAC1	5
  #define SI514_REG_M_FRAC2	6
  #define SI514_REG_M_FRAC3	7
  #define SI514_REG_M_INT_FRAC	8
  #define SI514_REG_M_INT		9
  #define SI514_REG_HS_DIV	10
  #define SI514_REG_LS_HS_DIV	11
  #define SI514_REG_OE_STATE	14
  #define SI514_REG_RESET		128
  #define SI514_REG_CONTROL	132
  
  /* Register values */
  #define SI514_RESET_RST		BIT(7)
  
  #define SI514_CONTROL_FCAL	BIT(0)
  #define SI514_CONTROL_OE	BIT(2)
  
  #define SI514_MIN_FREQ	    100000U
  #define SI514_MAX_FREQ	 250000000U
  
  #define FXO		  31980000U
  
  #define FVCO_MIN	2080000000U
  #define FVCO_MAX	2500000000U
  
  #define HS_DIV_MAX	1022
  
  struct clk_si514 {
  	struct clk_hw hw;
  	struct regmap *regmap;
  	struct i2c_client *i2c_client;
  };
  #define to_clk_si514(_hw)	container_of(_hw, struct clk_si514, hw)
  
  /* Multiplier/divider settings */
  struct clk_si514_muldiv {
  	u32 m_frac;  /* 29-bit Fractional part of multiplier M */
  	u8 m_int; /* Integer part of multiplier M, 65..78 */
  	u8 ls_div_bits; /* 2nd divider, as 2^x */
  	u16 hs_div; /* 1st divider, must be even and 10<=x<=1022 */
  };
  
  /* Enables or disables the output driver */
  static int si514_enable_output(struct clk_si514 *data, bool enable)
  {
  	return regmap_update_bits(data->regmap, SI514_REG_CONTROL,
  		SI514_CONTROL_OE, enable ? SI514_CONTROL_OE : 0);
  }
  
  /* Retrieve clock multiplier and dividers from hardware */
  static int si514_get_muldiv(struct clk_si514 *data,
  	struct clk_si514_muldiv *settings)
  {
  	int err;
  	u8 reg[7];
  
  	err = regmap_bulk_read(data->regmap, SI514_REG_M_FRAC1,
  			reg, ARRAY_SIZE(reg));
  	if (err)
  		return err;
  
  	settings->m_frac = reg[0] | reg[1] << 8 | reg[2] << 16 |
  			   (reg[3] & 0x1F) << 24;
  	settings->m_int = (reg[4] & 0x3f) << 3 | reg[3] >> 5;
  	settings->ls_div_bits = (reg[6] >> 4) & 0x07;
  	settings->hs_div = (reg[6] & 0x03) << 8 | reg[5];
  	return 0;
  }
  
  static int si514_set_muldiv(struct clk_si514 *data,
  	struct clk_si514_muldiv *settings)
  {
  	u8 lp;
  	u8 reg[7];
  	int err;
  
  	/* Calculate LP1/LP2 according to table 13 in the datasheet */
  	/* 65.259980246 */
  	if (settings->m_int < 65 ||
  		(settings->m_int == 65 && settings->m_frac <= 139575831))
  		lp = 0x22;
  	/* 67.859763463 */
  	else if (settings->m_int < 67 ||
  		(settings->m_int == 67 && settings->m_frac <= 461581994))
  		lp = 0x23;
  	/* 72.937624981 */
  	else if (settings->m_int < 72 ||
  		(settings->m_int == 72 && settings->m_frac <= 503383578))
  		lp = 0x33;
  	/* 75.843265046 */
  	else if (settings->m_int < 75 ||
  		(settings->m_int == 75 && settings->m_frac <= 452724474))
  		lp = 0x34;
  	else
  		lp = 0x44;
  
  	err = regmap_write(data->regmap, SI514_REG_LP, lp);
  	if (err < 0)
  		return err;
  
  	reg[0] = settings->m_frac;
  	reg[1] = settings->m_frac >> 8;
  	reg[2] = settings->m_frac >> 16;
  	reg[3] = settings->m_frac >> 24 | settings->m_int << 5;
  	reg[4] = settings->m_int >> 3;
  	reg[5] = settings->hs_div;
  	reg[6] = (settings->hs_div >> 8) | (settings->ls_div_bits << 4);
  
  	err = regmap_bulk_write(data->regmap, SI514_REG_HS_DIV, reg + 5, 2);
  	if (err < 0)
  		return err;
  	/*
  	 * Writing to SI514_REG_M_INT_FRAC triggers the clock change, so that
  	 * must be written last
  	 */
  	return regmap_bulk_write(data->regmap, SI514_REG_M_FRAC1, reg, 5);
  }
  
  /* Calculate divider settings for a given frequency */
  static int si514_calc_muldiv(struct clk_si514_muldiv *settings,
  	unsigned long frequency)
  {
  	u64 m;
  	u32 ls_freq;
  	u32 tmp;
  	u8 res;
  
  	if ((frequency < SI514_MIN_FREQ) || (frequency > SI514_MAX_FREQ))
  		return -EINVAL;
  
  	/* Determine the minimum value of LS_DIV and resulting target freq. */
  	ls_freq = frequency;
  	if (frequency >= (FVCO_MIN / HS_DIV_MAX))
  		settings->ls_div_bits = 0;
  	else {
  		res = 1;
  		tmp = 2 * HS_DIV_MAX;
  		while (tmp <= (HS_DIV_MAX * 32)) {
  			if ((frequency * tmp) >= FVCO_MIN)
  				break;
  			++res;
  			tmp <<= 1;
  		}
  		settings->ls_div_bits = res;
  		ls_freq = frequency << res;
  	}
  
  	/* Determine minimum HS_DIV, round up to even number */
  	settings->hs_div = DIV_ROUND_UP(FVCO_MIN >> 1, ls_freq) << 1;
  
  	/* M = LS_DIV x HS_DIV x frequency / F_XO (in fixed-point) */
  	m = ((u64)(ls_freq * settings->hs_div) << 29) + (FXO / 2);
  	do_div(m, FXO);
  	settings->m_frac = (u32)m & (BIT(29) - 1);
  	settings->m_int = (u32)(m >> 29);
  
  	return 0;
  }
  
  /* Calculate resulting frequency given the register settings */
  static unsigned long si514_calc_rate(struct clk_si514_muldiv *settings)
  {
  	u64 m = settings->m_frac | ((u64)settings->m_int << 29);
  	u32 d = settings->hs_div * BIT(settings->ls_div_bits);
  
  	return ((u32)(((m * FXO) + (FXO / 2)) >> 29)) / d;
  }
  
  static unsigned long si514_recalc_rate(struct clk_hw *hw,
  		unsigned long parent_rate)
  {
  	struct clk_si514 *data = to_clk_si514(hw);
  	struct clk_si514_muldiv settings;
  	int err;
  
  	err = si514_get_muldiv(data, &settings);
  	if (err) {
  		dev_err(&data->i2c_client->dev, "unable to retrieve settings
  ");
  		return 0;
  	}
  
  	return si514_calc_rate(&settings);
  }
  
  static long si514_round_rate(struct clk_hw *hw, unsigned long rate,
  		unsigned long *parent_rate)
  {
  	struct clk_si514_muldiv settings;
  	int err;
  
  	if (!rate)
  		return 0;
  
  	err = si514_calc_muldiv(&settings, rate);
  	if (err)
  		return err;
  
  	return si514_calc_rate(&settings);
  }
  
  /*
   * Update output frequency for big frequency changes (> 1000 ppm).
   * The chip supports <1000ppm changes "on the fly", we haven't implemented
   * that here.
   */
  static int si514_set_rate(struct clk_hw *hw, unsigned long rate,
  		unsigned long parent_rate)
  {
  	struct clk_si514 *data = to_clk_si514(hw);
  	struct clk_si514_muldiv settings;
  	int err;
  
  	err = si514_calc_muldiv(&settings, rate);
  	if (err)
  		return err;
  
  	si514_enable_output(data, false);
  
  	err = si514_set_muldiv(data, &settings);
  	if (err < 0)
  		return err; /* Undefined state now, best to leave disabled */
  
  	/* Trigger calibration */
  	err = regmap_write(data->regmap, SI514_REG_CONTROL, SI514_CONTROL_FCAL);
  	if (err < 0)
  		return err;
  
  	/* Applying a new frequency can take up to 10ms */
  	usleep_range(10000, 12000);
  
  	si514_enable_output(data, true);
  
  	return err;
  }
  
  static const struct clk_ops si514_clk_ops = {
  	.recalc_rate = si514_recalc_rate,
  	.round_rate = si514_round_rate,
  	.set_rate = si514_set_rate,
  };
  
  static bool si514_regmap_is_volatile(struct device *dev, unsigned int reg)
  {
  	switch (reg) {
  	case SI514_REG_CONTROL:
  	case SI514_REG_RESET:
  		return true;
  	default:
  		return false;
  	}
  }
  
  static bool si514_regmap_is_writeable(struct device *dev, unsigned int reg)
  {
  	switch (reg) {
  	case SI514_REG_LP:
  	case SI514_REG_M_FRAC1 ... SI514_REG_LS_HS_DIV:
  	case SI514_REG_OE_STATE:
  	case SI514_REG_RESET:
  	case SI514_REG_CONTROL:
  		return true;
  	default:
  		return false;
  	}
  }
  
  static const struct regmap_config si514_regmap_config = {
  	.reg_bits = 8,
  	.val_bits = 8,
  	.cache_type = REGCACHE_RBTREE,
  	.max_register = SI514_REG_CONTROL,
  	.writeable_reg = si514_regmap_is_writeable,
  	.volatile_reg = si514_regmap_is_volatile,
  };
  
  static int si514_probe(struct i2c_client *client,
  		const struct i2c_device_id *id)
  {
  	struct clk_si514 *data;
  	struct clk_init_data init;
  	struct clk *clk;
  	int err;
  
  	data = devm_kzalloc(&client->dev, sizeof(*data), GFP_KERNEL);
  	if (!data)
  		return -ENOMEM;
  
  	init.ops = &si514_clk_ops;
  	init.flags = CLK_IS_ROOT;
  	init.num_parents = 0;
  	data->hw.init = &init;
  	data->i2c_client = 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, &si514_regmap_config);
  	if (IS_ERR(data->regmap)) {
  		dev_err(&client->dev, "failed to allocate register map
  ");
  		return PTR_ERR(data->regmap);
  	}
  
  	i2c_set_clientdata(client, data);
  
  	clk = devm_clk_register(&client->dev, &data->hw);
  	if (IS_ERR(clk)) {
  		dev_err(&client->dev, "clock registration failed
  ");
  		return PTR_ERR(clk);
  	}
  	err = of_clk_add_provider(client->dev.of_node, of_clk_src_simple_get,
  			clk);
  	if (err) {
  		dev_err(&client->dev, "unable to add clk provider
  ");
  		return err;
  	}
  
  	return 0;
  }
  
  static int si514_remove(struct i2c_client *client)
  {
  	of_clk_del_provider(client->dev.of_node);
  	return 0;
  }
  
  static const struct i2c_device_id si514_id[] = {
  	{ "si514", 0 },
  	{ }
  };
  MODULE_DEVICE_TABLE(i2c, si514_id);
  
  static const struct of_device_id clk_si514_of_match[] = {
  	{ .compatible = "silabs,si514" },
  	{ },
  };
  MODULE_DEVICE_TABLE(of, clk_si514_of_match);
  
  static struct i2c_driver si514_driver = {
  	.driver = {
  		.name = "si514",
  		.of_match_table = clk_si514_of_match,
  	},
  	.probe		= si514_probe,
  	.remove		= si514_remove,
  	.id_table	= si514_id,
  };
  module_i2c_driver(si514_driver);
  
  MODULE_AUTHOR("Mike Looijmans <mike.looijmans@topic.nl>");
  MODULE_DESCRIPTION("Si514 driver");
  MODULE_LICENSE("GPL");