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SubjectRe: [PATCH] clk: Add driver for the si544 clock generator chip
Date
Quoting Mike Looijmans (2018-03-13 01:43:59)
> diff --git a/Documentation/devicetree/bindings/clock/silabs,si544.txt b/Documentation/devicetree/bindings/clock/silabs,si544.txt
> new file mode 100644
> index 0000000..eec1787
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/clock/silabs,si544.txt
> @@ -0,0 +1,25 @@
> +Binding for Silicon Labs 544 programmable I2C clock generator.
> +
> +Reference
> +This binding uses the common clock binding[1]. Details about the device can be
> +found in the datasheet[2].
> +
> +[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
> +[2] Si544 datasheet
> + https://www.silabs.com/documents/public/data-sheets/si544-datasheet.pdf

Can this reference stuff go to the bottom of this document?

> +
> +Required properties:
> + - compatible: One of "silabs,si514a", "silabs,si514b" "silabs,si514c" according
> + to the speed grade of the chip.
> + - reg: I2C device address.
> + - #clock-cells: From common clock bindings: Shall be 0.
> +
> +Optional properties:
> + - clock-output-names: From common clock bindings. Recommended to be "si544".
> +
> +Example:
> + si544: clock-generator@55 {

I'm not sure clock-generator is in the list of node names, but we have
some of these already so alright.

> + reg = <0x55>;
> + #clock-cells = <0>;
> + compatible = "silabs,si544b";
> + };
> diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
> index 98ce9fc..5c7dc8e 100644
> --- a/drivers/clk/Kconfig
> +++ b/drivers/clk/Kconfig
> @@ -91,6 +91,16 @@ config COMMON_CLK_SI514
> This driver supports the Silicon Labs 514 programmable clock
> generator.
>
> +config COMMON_CLK_SI544
> + tristate "Clock driver for SiLabs 544 devices"
> + depends on I2C
> + depends on OF

Does it depend on anything in OF to build?

> + select REGMAP_I2C
> + help
> + ---help---
> + This driver supports the Silicon Labs 544 programmable clock
> + generator.
> +
> config COMMON_CLK_SI570
> tristate "Clock driver for SiLabs 570 and compatible devices"
> depends on I2C
> diff --git a/drivers/clk/clk-si544.c b/drivers/clk/clk-si544.c
> new file mode 100644
> index 0000000..1947e48
> --- /dev/null
> +++ b/drivers/clk/clk-si544.c
> @@ -0,0 +1,421 @@
> +/*
> + * Driver for Silicon Labs Si544 Programmable Oscillator
> + *
> + * Copyright (C) 2018 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.

Can we have SPDX style license here?

> + */
> +
> +#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 (decimal as in datasheet) */

Heh.

> +#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 oscilator 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
> +
> +enum si544_speed_grade {
> + si544a,
> + si544b,
> + si544c,
> +};
> +
> +struct clk_si544 {
> + struct clk_hw hw;
> + struct regmap *regmap;
> + struct i2c_client *i2c_client;
> + enum si544_speed_grade speed_grade;
> +};
> +#define to_clk_si544(_hw) container_of(_hw, struct clk_si544, hw)
> +
> +/* Multiplier/divider settings */
> +struct clk_si544_muldiv {
> + u32 fb_div_frac; /* Integer part of feedback divider (32 bits) */
> + u16 fb_div_int; /* Fractional part of feedback divider (11 bits) */
> + u16 hs_div; /* 1st divider, 5..2046, must be even when >33 */
> + u8 ls_div_bits; /* 2nd divider, as 2^x, range 0..5 */
> +};

Can you use kernel-doc style instead of inline comments please.

> +
> +static bool is_valid_frequency(const struct clk_si544 *data,
> + unsigned long frequency)
> +{
> + unsigned long max_freq;
> +
> + if (frequency < SI544_MIN_FREQ)
> + return false;
> +
> + switch (data->speed_grade) {
> + case si544a:
> + max_freq = 1500000000;
> + break;
> + case si544b:
> + max_freq = 800000000;
> + break;
> + case si544c:
> + max_freq = 350000000;
> + break;
> + default:
> + return false;

Drop this default case and let the compiler complain if we get a new
enum to handle.

> + }
> +
> + if (frequency > max_freq)
> + return false;
> +
> + return true;

Replace with 'return frequency <= 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 >= (FVCO_MIN / HS_DIV_MAX))

Maybe FVCO_MIN/HS_DIV_MAX has a name that can be defined? MIN_DIV_FREQ?

> + settings->ls_div_bits = 0;
> + else {

Style: Please add braces on the if arm too.

> + 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 by rounding up */
> + vco = FVCO_MIN + ls_freq - 1;
> + do_div(vco, ls_freq);
> + settings->hs_div = vco;
> + /* round up to even number if needed */
> + if ((settings->hs_div > HS_DIV_MAX_ODD) && (settings->hs_div & 1))

Drop useless parenthesis please.

> + ++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;
> + do_div(vco, FXO);
> + settings->fb_div_frac = vco;

This is all packed together. Please add a newline before each comment to
make it easier to read.

> +
> + return 0;
> +}
> +
> +/* Calculate resulting frequency given the register settings */
> +static unsigned long si544_calc_rate(struct clk_si544_muldiv *settings)
> +{
> + u32 d = settings->hs_div * BIT(settings->ls_div_bits);
> + u64 vco;
> +
> + /* Calculate VCO while preventing overflow */
> + vco = (u64)settings->fb_div_int * FXO;
> + vco += (((u64)settings->fb_div_frac * FXO) + (FXO / 2)) >> 32;

Yay for the smatch checking stuff on the list! Try to put things on more
lines to keep stuff easier to follow.

> +
> + do_div(vco, d);
> +
> + return vco;
> +}
> +
> +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) {
> + dev_err(&data->i2c_client->dev, "unable to retrieve settings\n");

This error message could become quite spammy given that we typically
call recalc_rate() many times.

> + return 0;
> + }
> +
> + return si544_calc_rate(&settings);
> +}
> +
> +static long si544_round_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;
> + int err;
> +
> + if (!rate)
> + return 0;

Why? Do certain drivers call round_rate() with 0 and we want to ignore
those cases and not return an error?

> +
> + if (!is_valid_frequency(data, rate))
> + return -EINVAL;
> +
> + err = si544_calc_muldiv(&settings, rate);
> + if (err)
> + return err;
> +
> + return si544_calc_rate(&settings);
> +}
> +
> +
[...]
> +
> +static int si544_probe(struct i2c_client *client,
> + const struct i2c_device_id *id)
> +{
> + 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->speed_grade = id->driver_data;
> +
> + 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)) {
> + dev_err(&client->dev, "failed to allocate register map\n");

Do we need another allocation failure message?

> + 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 = of_clk_add_hw_provider(client->dev.of_node, of_clk_hw_simple_get,

devm_of_clk_add_hw_provider()?

> + &data->hw);
> + if (err) {
> + dev_err(&client->dev, "unable to add clk provider\n");
> + return err;
> + }
> +
> + return 0;
> +}
> +
> +static int si544_remove(struct i2c_client *client)
> +{
> + of_clk_del_provider(client->dev.of_node);
> + return 0;
> +}

Drop?

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