LinuxLists.cc - [PATCH v2] clk: si570: Add a driver for SI570 oscillators

2013-09-18 22:44:14

Subject: [PATCH v2] 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.

Cc: Guenter Roeck <[email protected]>
Signed-off-by: Soren Brinkmann <[email protected]>
---
v2:
- document clock-output-names in bindings documentation
- don't use wildcards in compatibility string
- change Kconfig entry to "... 570 and compatible devices"
- change some indentation flaws
- use 10000 as MIN and MAX value in usleep_range
- fail probe() if 'factory-fout' is not provided in DT
- default factory fout #defines removed
- use i2c driver_data instead of OF data
- remove some related structs and data
- rename DT property 'initial-fout' => 'clock-frequency' (like si5351
driver)
- add some more details regarding the 'factory-fout' DT property

.../devicetree/bindings/clock/silabs,si570.txt | 38 ++
drivers/clk/Kconfig | 10 +
drivers/clk/Makefile | 1 +
drivers/clk/clk-si570.c | 517 +++++++++++++++++++++
4 files changed, 566 insertions(+)
create mode 100644 Documentation/devicetree/bindings/clock/silabs,si570.txt
create mode 100644 drivers/clk/clk-si570.c

diff --git a/Documentation/devicetree/bindings/clock/silabs,si570.txt b/Documentation/devicetree/bindings/clock/silabs,si570.txt
new file mode 100644
index 0000000..7ab5c8b
--- /dev/null
+++ b/Documentation/devicetree/bindings/clock/silabs,si570.txt
@@ -0,0 +1,38 @@
+Binding for Silicon Labs 570, 571, 598 and 599 programmable
+I2C clock generators.
+
+Reference
+This binding uses the common clock binding[1]. Details about the devices can be
+found in the data sheets[2][3].
+
+[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
+[2] Si570/571 Data Sheet
+ http://www.silabs.com/Support%20Documents/TechnicalDocs/si570.pdf
+[3] Si598/599 Data Sheet
+ http://www.silabs.com/Support%20Documents/TechnicalDocs/si598-99.pdf
+
+Required properties:
+ - compatible: Shall be one of "silabs,si570", "silabs,si571",
+ "silabs,si598", "silabs,si599"
+ - reg: I2C device address.
+ - #clock-cells: From common clock bindings: Shall be 0.
+ - factory-fout: Factory set default frequency. This frequency is part specific.
+ The correct frequency for the part used has to be provided in
+ order to generate the correct output frequencies. For more
+ details, please refer to the data sheet.
+
+Optional properties:
+ - clock-output-names: From common clock bindings. Recommended to be "si570".
+ - clock-frequency: Output frequency to generate. This defines the output
+ frequency set during boot. It can be reprogrammed during
+ runtime using the common clock framework.
+ - temperature-stability-7ppm: Indicate a device with a temperature stability
+ of 7ppm
+
+Example:
+ si570: clock-generator@5d {
+ #clock-cells = <0>;
+ compatible = "silabs,si570";
+ reg = <0x5d>;
+ factory-fout = <156250000>;
+ };
diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
index 279407a..349b88a 100644
--- a/drivers/clk/Kconfig
+++ b/drivers/clk/Kconfig
@@ -64,6 +64,16 @@ config COMMON_CLK_SI5351
This driver supports Silicon Labs 5351A/B/C programmable clock
generators.

+config COMMON_CLK_SI570
+ tristate "Clock driver for SiLabs 570 and compatible devices"
+ depends on I2C
+ depends on OF
+ select REGMAP_I2C
+ help
+ ---help---
+ This driver supports Silicon Labs 570/571/598/599 programmable
+ clock generators.
+
config COMMON_CLK_S2MPS11
tristate "Clock driver for S2MPS11 MFD"
depends on MFD_SEC_CORE
diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
index 7b11106..c0e94b3 100644
--- a/drivers/clk/Makefile
+++ b/drivers/clk/Makefile
@@ -40,6 +40,7 @@ obj-$(CONFIG_COMMON_CLK_AXI_CLKGEN) += clk-axi-clkgen.o
obj-$(CONFIG_COMMON_CLK_WM831X) += clk-wm831x.o
obj-$(CONFIG_COMMON_CLK_MAX77686) += clk-max77686.o
obj-$(CONFIG_COMMON_CLK_SI5351) += clk-si5351.o
+obj-$(CONFIG_COMMON_CLK_SI570) += clk-si570.o
obj-$(CONFIG_COMMON_CLK_S2MPS11) += clk-s2mps11.o
obj-$(CONFIG_CLK_TWL6040) += clk-twl6040.o
obj-$(CONFIG_CLK_PPC_CORENET) += clk-ppc-corenet.o
diff --git a/drivers/clk/clk-si570.c b/drivers/clk/clk-si570.c
new file mode 100644
index 0000000..c20dfce
--- /dev/null
+++ b/drivers/clk/clk-si570.c
@@ -0,0 +1,517 @@
+/*
+ * 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 <[email protected]>
+ * Sören Brinkmann <[email protected]>
+ *
+ * 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)
+
+/**
+ * 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, 10000);
+
+ 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);
+
+ 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_warn(&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 135:
+ return true;
+ default:
+ return false;
+ }
+}
+
+static bool si570_regmap_is_writeable(struct device *dev, unsigned int reg)
+{
+ switch (reg) {
+ case 7 ... 18:
+ case 135:
+ case 137:
+ 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;
+ int err;
+
+ 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->max_freq = id->driver_data;
+ data->i2c_client = client;
+
+ if (of_property_read_bool(client->dev.of_node,
+ "temperature-stability-7ppm"))
+ data->div_offset = SI570_DIV_OFFSET_7PPM;
+
+ 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 fout from either platform data or the
+ * device tree
+ */
+ if (!of_property_read_u32(client->dev.of_node, "clock-frequency",
+ &initial_fout)) {
+ err = clk_set_rate(clk, initial_fout);
+ if (err)
+ dev_warn(&client->dev,
+ "unable to set initial output frequency %u: %d\n",
+ initial_fout, 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)
+{
+ struct clk_si570 *data = i2c_get_clientdata(client);
+
+ of_clk_del_provider(client->dev.of_node);
+ clk_unregister(data->hw.clk);
+
+ return 0;
+}
+
+static const struct i2c_device_id si570_id[] = {
+ { "si570", SI570_MAX_FREQ },
+ { "si571", SI570_MAX_FREQ },
+ { "si598", SI598_MAX_FREQ },
+ { "si599", SI598_MAX_FREQ },
+ { }
+};
+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 <[email protected]>");
+MODULE_AUTHOR("Soeren Brinkmann <[email protected]");
+MODULE_DESCRIPTION("Si570 driver");
+MODULE_LICENSE("GPL");
--
1.8.4

2013-09-18 22:44:44

by Soren Brinkmann

[permalink] [raw]

On Thu, Sep 19, 2013 at 02:15:35PM -0700, Guenter Roeck wrote:
> On Thu, Sep 19, 2013 at 11:05:12AM -0700, Mike Turquette wrote:
> > Quoting Soren Brinkmann (2013-09-18 15:43:38)
> > > diff --git a/Documentation/devicetree/bindings/clock/silabs,si570.txt b/Documentation/devicetree/bindings/clock/silabs,si570.txt
> > > new file mode 100644
> > > index 0000000..7ab5c8b
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/clock/silabs,si570.txt
> > > @@ -0,0 +1,38 @@
> > > +Binding for Silicon Labs 570, 571, 598 and 599 programmable
> > > +I2C clock generators.
> > > +
> > > +Reference
> > > +This binding uses the common clock binding[1]. Details about the devices can be
> > > +found in the data sheets[2][3].
> > > +
> > > +[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
> > > +[2] Si570/571 Data Sheet
> > > + http://www.silabs.com/Support%20Documents/TechnicalDocs/si570.pdf
> > > +[3] Si598/599 Data Sheet
> > > + http://www.silabs.com/Support%20Documents/TechnicalDocs/si598-99.pdf
> > > +
> > > +Required properties:
> > > + - compatible: Shall be one of "silabs,si570", "silabs,si571",
> > > + "silabs,si598", "silabs,si599"
> > > + - reg: I2C device address.
> > > + - #clock-cells: From common clock bindings: Shall be 0.
> > > + - factory-fout: Factory set default frequency. This frequency is part specific.
> > > + The correct frequency for the part used has to be provided in
> > > + order to generate the correct output frequencies. For more
> > > + details, please refer to the data sheet.
> > > +
> > > +Optional properties:
> > > + - clock-output-names: From common clock bindings. Recommended to be "si570".
> > > + - clock-frequency: Output frequency to generate. This defines the output
> > > + frequency set during boot. It can be reprogrammed during
> > > + runtime using the common clock framework.
> > > + - temperature-stability-7ppm: Indicate a device with a temperature stability
> > > + of 7ppm
> >
> > Some DT binding bike-shedding:
> >
> > Should this be "temperature-stability-ppm = <7>;" ? Do you think that
> > this value might change in the future?
> >
> Valid values are 7, 20, and 50 as far as I know. Problem is that the value is
> not used directly, but only to hint that a specific set of registers shall be
> used.
>
> Given that, it may in fact be better to use an explicit number. Even though the
> two register sets are specified by <7> in one case and <20,50> in the other
> today, there may at some point be yet another value which might use the 7 ppm
> register set or the 20/50 ppm register set ... or yet another register set.
> An explicit number would cover all future accuracy ranges, not just the
> existing ones.
Okay, I'm convinced. Changing that, I'd also make it a mandatory
property.

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