clk: si570: Add a driver for SI570 oscillators

Add a driver for SILabs 570, 571, 598, 599 programmable oscillators.
The devices generate low-jitter clock signals and are reprogrammable via
an I2C interface.

Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

1 files changed, 531 insertions, 0 deletions

diff --git a/drivers/clk/clk-si570.c b/drivers/clk/clk-si570.c
new file mode 100644
index 000000000000..5d0ac9f8e1ee
--- /dev/null
+++ b/drivers/clk/clk-si570.c
@@ -0,0 +1,531 @@
+/*
+ * Driver for Silicon Labs Si570/Si571 Programmable XO/VCXO
+ *
+ * Copyright (C) 2010, 2011 Ericsson AB.
+ * Copyright (C) 2011 Guenter Roeck.
+ * Copyright (C) 2011 - 2013 Xilinx Inc.
+ *
+ * Author: Guenter Roeck <guenter.roeck@ericsson.com>
+ *	   Sören Brinkmann <soren.brinkmann@xilinx.com>
+ *
+ * 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>
+
+/* Si570 registers */
+#define SI570_REG_HS_N1		7
+#define SI570_REG_N1_RFREQ0	8
+#define SI570_REG_RFREQ1	9
+#define SI570_REG_RFREQ2	10
+#define SI570_REG_RFREQ3	11
+#define SI570_REG_RFREQ4	12
+#define SI570_REG_CONTROL	135
+#define SI570_REG_FREEZE_DCO	137
+#define SI570_DIV_OFFSET_7PPM	6
+
+#define HS_DIV_SHIFT		5
+#define HS_DIV_MASK		0xe0
+#define HS_DIV_OFFSET		4
+#define N1_6_2_MASK		0x1f
+#define N1_1_0_MASK		0xc0
+#define RFREQ_37_32_MASK	0x3f
+
+#define SI570_MIN_FREQ		10000000L
+#define SI570_MAX_FREQ		1417500000L
+#define SI598_MAX_FREQ		525000000L
+
+#define FDCO_MIN		4850000000LL
+#define FDCO_MAX		5670000000LL
+
+#define SI570_CNTRL_RECALL	(1 << 0)
+#define SI570_CNTRL_FREEZE_M	(1 << 5)
+#define SI570_CNTRL_NEWFREQ	(1 << 6)
+
+#define SI570_FREEZE_DCO	(1 << 4)
+
+/**
+ * struct clk_si570:
+ * @hw:	Clock hw struct
+ * @regmap:	Device's regmap
+ * @div_offset:	Rgister offset for dividers
+ * @max_freq:	Maximum frequency for this device
+ * @fxtal:	Factory xtal frequency
+ * @n1:		Clock divider N1
+ * @hs_div:	Clock divider HSDIV
+ * @rfreq:	Clock multiplier RFREQ
+ * @frequency:	Current output frequency
+ * @i2c_client:	I2C client pointer
+ */
+struct clk_si570 {
+	struct clk_hw hw;
+	struct regmap *regmap;
+	unsigned int div_offset;
+	u64 max_freq;
+	u64 fxtal;
+	unsigned int n1;
+	unsigned int hs_div;
+	u64 rfreq;
+	u64 frequency;
+	struct i2c_client *i2c_client;
+};
+#define to_clk_si570(_hw)	container_of(_hw, struct clk_si570, hw)
+
+enum clk_si570_variant {
+	si57x,
+	si59x
+};
+
+/**
+ * si570_get_divs() - Read clock dividers from HW
+ * @data:	Pointer to struct clk_si570
+ * @rfreq:	Fractional multiplier (output)
+ * @n1:		Divider N1 (output)
+ * @hs_div:	Divider HSDIV (output)
+ * Returns 0 on success, negative errno otherwise.
+ *
+ * Retrieve clock dividers and multipliers from the HW.
+ */
+static int si570_get_divs(struct clk_si570 *data, u64 *rfreq,
+		unsigned int *n1, unsigned int *hs_div)
+{
+	int err;
+	u8 reg[6];
+	u64 tmp;
+
+	err = regmap_bulk_read(data->regmap, SI570_REG_HS_N1 + data->div_offset,
+			reg, ARRAY_SIZE(reg));
+	if (err)
+		return err;
+
+	*hs_div = ((reg[0] & HS_DIV_MASK) >> HS_DIV_SHIFT) + HS_DIV_OFFSET;
+	*n1 = ((reg[0] & N1_6_2_MASK) << 2) + ((reg[1] & N1_1_0_MASK) >> 6) + 1;
+	/* Handle invalid cases */
+	if (*n1 > 1)
+		*n1 &= ~1;
+
+	tmp = reg[1] & RFREQ_37_32_MASK;
+	tmp = (tmp << 8) + reg[2];
+	tmp = (tmp << 8) + reg[3];
+	tmp = (tmp << 8) + reg[4];
+	tmp = (tmp << 8) + reg[5];
+	*rfreq = tmp;
+
+	return 0;
+}
+
+/**
+ * si570_get_defaults() - Get default values
+ * @data:	Driver data structure
+ * @fout:	Factory frequency output
+ * Returns 0 on success, negative errno otherwise.
+ */
+static int si570_get_defaults(struct clk_si570 *data, u64 fout)
+{
+	int err;
+	u64 fdco;
+
+	regmap_write(data->regmap, SI570_REG_CONTROL, SI570_CNTRL_RECALL);
+
+	err = si570_get_divs(data, &data->rfreq, &data->n1, &data->hs_div);
+	if (err)
+		return err;
+
+	/*
+	 * Accept optional precision loss to avoid arithmetic overflows.
+	 * Acceptable per Silicon Labs Application Note AN334.
+	 */
+	fdco = fout * data->n1 * data->hs_div;
+	if (fdco >= (1LL << 36))
+		data->fxtal = div64_u64(fdco << 24, data->rfreq >> 4);
+	else
+		data->fxtal = div64_u64(fdco << 28, data->rfreq);
+
+	data->frequency = fout;
+
+	return 0;
+}
+
+/**
+ * si570_update_rfreq() - Update clock multiplier
+ * @data:	Driver data structure
+ * Passes on regmap_bulk_write() return value.
+ */
+static int si570_update_rfreq(struct clk_si570 *data)
+{
+	u8 reg[5];
+
+	reg[0] = ((data->n1 - 1) << 6) |
+		((data->rfreq >> 32) & RFREQ_37_32_MASK);
+	reg[1] = (data->rfreq >> 24) & 0xff;
+	reg[2] = (data->rfreq >> 16) & 0xff;
+	reg[3] = (data->rfreq >> 8) & 0xff;
+	reg[4] = data->rfreq & 0xff;
+
+	return regmap_bulk_write(data->regmap, SI570_REG_N1_RFREQ0 +
+			data->div_offset, reg, ARRAY_SIZE(reg));
+}
+
+/**
+ * si570_calc_divs() - Caluclate clock dividers
+ * @frequency:	Target frequency
+ * @data:	Driver data structure
+ * @out_rfreq:	RFREG fractional multiplier (output)
+ * @out_n1:	Clock divider N1 (output)
+ * @out_hs_div:	Clock divider HSDIV (output)
+ * Returns 0 on success, negative errno otherwise.
+ *
+ * Calculate the clock dividers (@out_hs_div, @out_n1) and clock multiplier
+ * (@out_rfreq) for a given target @frequency.
+ */
+static int si570_calc_divs(unsigned long frequency, struct clk_si570 *data,
+		u64 *out_rfreq, unsigned int *out_n1, unsigned int *out_hs_div)
+{
+	int i;
+	unsigned int n1, hs_div;
+	u64 fdco, best_fdco = ULLONG_MAX;
+	static const uint8_t si570_hs_div_values[] = { 11, 9, 7, 6, 5, 4 };
+
+	for (i = 0; i < ARRAY_SIZE(si570_hs_div_values); i++) {
+		hs_div = si570_hs_div_values[i];
+		/* Calculate lowest possible value for n1 */
+		n1 = div_u64(div_u64(FDCO_MIN, hs_div), frequency);
+		if (!n1 || (n1 & 1))
+			n1++;
+		while (n1 <= 128) {
+			fdco = (u64)frequency * (u64)hs_div * (u64)n1;
+			if (fdco > FDCO_MAX)
+				break;
+			if (fdco >= FDCO_MIN && fdco < best_fdco) {
+				*out_n1 = n1;
+				*out_hs_div = hs_div;
+				*out_rfreq = div64_u64(fdco << 28, data->fxtal);
+				best_fdco = fdco;
+			}
+			n1 += (n1 == 1 ? 1 : 2);
+		}
+	}
+
+	if (best_fdco == ULLONG_MAX)
+		return -EINVAL;
+
+	return 0;
+}
+
+static unsigned long si570_recalc_rate(struct clk_hw *hw,
+		unsigned long parent_rate)
+{
+	int err;
+	u64 rfreq, rate;
+	unsigned int n1, hs_div;
+	struct clk_si570 *data = to_clk_si570(hw);
+
+	err = si570_get_divs(data, &rfreq, &n1, &hs_div);
+	if (err) {
+		dev_err(&data->i2c_client->dev, "unable to recalc rate\n");
+		return data->frequency;
+	}
+
+	rfreq = div_u64(rfreq, hs_div * n1);
+	rate = (data->fxtal * rfreq) >> 28;
+
+	return rate;
+}
+
+static long si570_round_rate(struct clk_hw *hw, unsigned long rate,
+		unsigned long *parent_rate)
+{
+	int err;
+	u64 rfreq;
+	unsigned int n1, hs_div;
+	struct clk_si570 *data = to_clk_si570(hw);
+
+	if (!rate)
+		return 0;
+
+	if (div64_u64(abs(rate - data->frequency) * 10000LL,
+				data->frequency) < 35) {
+		rfreq = div64_u64((data->rfreq * rate) +
+				div64_u64(data->frequency, 2), data->frequency);
+		n1 = data->n1;
+		hs_div = data->hs_div;
+
+	} else {
+		err = si570_calc_divs(rate, data, &rfreq, &n1, &hs_div);
+		if (err) {
+			dev_err(&data->i2c_client->dev,
+					"unable to round rate\n");
+			return 0;
+		}
+	}
+
+	return rate;
+}
+
+/**
+ * si570_set_frequency() - Adjust output frequency
+ * @data:	Driver data structure
+ * @frequency:	Target frequency
+ * Returns 0 on success.
+ *
+ * Update output frequency for big frequency changes (> 3,500 ppm).
+ */
+static int si570_set_frequency(struct clk_si570 *data, unsigned long frequency)
+{
+	int err;
+
+	err = si570_calc_divs(frequency, data, &data->rfreq, &data->n1,
+			&data->hs_div);
+	if (err)
+		return err;
+
+	/*
+	 * The DCO reg should be accessed with a read-modify-write operation
+	 * per AN334
+	 */
+	regmap_write(data->regmap, SI570_REG_FREEZE_DCO, SI570_FREEZE_DCO);
+	regmap_write(data->regmap, SI570_REG_HS_N1 + data->div_offset,
+			((data->hs_div - HS_DIV_OFFSET) << HS_DIV_SHIFT) |
+			(((data->n1 - 1) >> 2) & N1_6_2_MASK));
+	si570_update_rfreq(data);
+	regmap_write(data->regmap, SI570_REG_FREEZE_DCO, 0);
+	regmap_write(data->regmap, SI570_REG_CONTROL, SI570_CNTRL_NEWFREQ);
+
+	/* Applying a new frequency can take up to 10ms */
+	usleep_range(10000, 12000);
+
+	return 0;
+}
+
+/**
+ * si570_set_frequency_small() - Adjust output frequency
+ * @data:	Driver data structure
+ * @frequency:	Target frequency
+ * Returns 0 on success.
+ *
+ * Update output frequency for small frequency changes (< 3,500 ppm).
+ */
+static int si570_set_frequency_small(struct clk_si570 *data,
+				     unsigned long frequency)
+{
+	/*
+	 * This is a re-implementation of DIV_ROUND_CLOSEST
+	 * using the div64_u64 function lieu of letting the compiler
+	 * insert EABI calls
+	 */
+	data->rfreq = div64_u64((data->rfreq * frequency) +
+			div_u64(data->frequency, 2), data->frequency);
+	regmap_write(data->regmap, SI570_REG_CONTROL, SI570_CNTRL_FREEZE_M);
+	si570_update_rfreq(data);
+	regmap_write(data->regmap, SI570_REG_CONTROL, 0);
+
+	/* Applying a new frequency (small change) can take up to 100us */
+	usleep_range(100, 200);
+
+	return 0;
+}
+
+static int si570_set_rate(struct clk_hw *hw, unsigned long rate,
+		unsigned long parent_rate)
+{
+	struct clk_si570 *data = to_clk_si570(hw);
+	struct i2c_client *client = data->i2c_client;
+	int err;
+
+	if (rate < SI570_MIN_FREQ || rate > data->max_freq) {
+		dev_err(&client->dev,
+			"requested frequency %lu Hz is out of range\n", rate);
+		return -EINVAL;
+	}
+
+	if (div64_u64(abs(rate - data->frequency) * 10000LL,
+				data->frequency) < 35)
+		err = si570_set_frequency_small(data, rate);
+	else
+		err = si570_set_frequency(data, rate);
+
+	if (err)
+		return err;
+
+	data->frequency = rate;
+
+	return 0;
+}
+
+static const struct clk_ops si570_clk_ops = {
+	.recalc_rate = si570_recalc_rate,
+	.round_rate = si570_round_rate,
+	.set_rate = si570_set_rate,
+};
+
+static bool si570_regmap_is_volatile(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case SI570_REG_CONTROL:
+		return true;
+	default:
+		return false;
+	}
+}
+
+static bool si570_regmap_is_writeable(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case SI570_REG_HS_N1 ... (SI570_REG_RFREQ4 + SI570_DIV_OFFSET_7PPM):
+	case SI570_REG_CONTROL:
+	case SI570_REG_FREEZE_DCO:
+		return true;
+	default:
+		return false;
+	}
+}
+
+static struct regmap_config si570_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.cache_type = REGCACHE_RBTREE,
+	.max_register = 137,
+	.writeable_reg = si570_regmap_is_writeable,
+	.volatile_reg = si570_regmap_is_volatile,
+};
+
+static int si570_probe(struct i2c_client *client,
+		const struct i2c_device_id *id)
+{
+	struct clk_si570 *data;
+	struct clk_init_data init;
+	struct clk *clk;
+	u32 initial_fout, factory_fout, stability;
+	int err;
+	enum clk_si570_variant variant = id->driver_data;
+
+	data = devm_kzalloc(&client->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	init.ops = &si570_clk_ops;
+	init.flags = CLK_IS_ROOT;
+	init.num_parents = 0;
+	data->hw.init = &init;
+	data->i2c_client = client;
+
+	if (variant == si57x) {
+		err = of_property_read_u32(client->dev.of_node,
+				"temperature-stability", &stability);
+		if (err) {
+			dev_err(&client->dev,
+				  "'temperature-stability' property missing\n");
+			return err;
+		}
+		/* adjust register offsets for 7ppm devices */
+		if (stability == 7)
+			data->div_offset = SI570_DIV_OFFSET_7PPM;
+
+		data->max_freq = SI570_MAX_FREQ;
+	} else {
+		data->max_freq = SI598_MAX_FREQ;
+	}
+
+	if (of_property_read_string(client->dev.of_node, "clock-output-names",
+			&init.name))
+		init.name = client->dev.of_node->name;
+
+	err = of_property_read_u32(client->dev.of_node, "factory-fout",
+			&factory_fout);
+	if (err) {
+		dev_err(&client->dev, "'factory-fout' property missing\n");
+		return err;
+	}
+
+	data->regmap = devm_regmap_init_i2c(client, &si570_regmap_config);
+	if (IS_ERR(data->regmap)) {
+		dev_err(&client->dev, "failed to allocate register map\n");
+		return PTR_ERR(data->regmap);
+	}
+
+	i2c_set_clientdata(client, data);
+	err = si570_get_defaults(data, factory_fout);
+	if (err)
+		return err;
+
+	clk = devm_clk_register(&client->dev, &data->hw);
+	if (IS_ERR(clk)) {
+		dev_err(&client->dev, "clock registration failed\n");
+		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\n");
+		return err;
+	}
+
+	/* Read the requested initial output frequency from device tree */
+	if (!of_property_read_u32(client->dev.of_node, "clock-frequency",
+				&initial_fout)) {
+		err = clk_set_rate(clk, initial_fout);
+		if (err) {
+			of_clk_del_provider(client->dev.of_node);
+			return err;
+		}
+	}
+
+	/* Display a message indicating that we've successfully registered */
+	dev_info(&client->dev, "registered, current frequency %llu Hz\n",
+			data->frequency);
+
+	return 0;
+}
+
+static int si570_remove(struct i2c_client *client)
+{
+	of_clk_del_provider(client->dev.of_node);
+	return 0;
+}
+
+static const struct i2c_device_id si570_id[] = {
+	{ "si570", si57x },
+	{ "si571", si57x },
+	{ "si598", si59x },
+	{ "si599", si59x },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, si570_id);
+
+static const struct of_device_id clk_si570_of_match[] = {
+	{ .compatible = "silabs,si570" },
+	{ .compatible = "silabs,si571" },
+	{ .compatible = "silabs,si598" },
+	{ .compatible = "silabs,si599" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, clk_si570_of_match);
+
+static struct i2c_driver si570_driver = {
+	.driver = {
+		.name = "si570",
+		.of_match_table = of_match_ptr(clk_si570_of_match),
+	},
+	.probe		= si570_probe,
+	.remove		= si570_remove,
+	.id_table	= si570_id,
+};
+module_i2c_driver(si570_driver);
+
+MODULE_AUTHOR("Guenter Roeck <guenter.roeck@ericsson.com>");
+MODULE_AUTHOR("Soeren Brinkmann <soren.brinkmann@xilinx.com");
+MODULE_DESCRIPTION("Si570 driver");
+MODULE_LICENSE("GPL");