Re: [v4 2/2] pwm: Add Aspeed ast2600 PWM support

From: Uwe Kleine-König
Date: Mon May 10 2021 - 08:52:04 EST

Hello,

On Mon, May 10, 2021 at 03:35:11PM +0800, Billy Tsai wrote:
> This patch add the support of PWM controller which can be found at aspeed
> ast2600 soc. The pwm supoorts up to 16 channels and it's part function
> of multi-function device "pwm-tach controller".
>
> Signed-off-by: Billy Tsai <billy_tsai@xxxxxxxxxxxxxx>
> ---
> drivers/pwm/Kconfig | 8 +
> drivers/pwm/Makefile | 1 +
> drivers/pwm/pwm-aspeed-g6.c | 368 ++++++++++++++++++++++++++++++++++++
> 3 files changed, 377 insertions(+)
> create mode 100644 drivers/pwm/pwm-aspeed-g6.c
>
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 63be5362fd3a..b0964b9a3273 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -51,6 +51,14 @@ config PWM_AB8500
> To compile this driver as a module, choose M here: the module
> will be called pwm-ab8500.
>
> +config PWM_ASPEED_G6
> + tristate "ASPEEDG6 PWM support"
> + depends on ARCH_ASPEED || COMPILE_TEST
> + help
> + Generic PWM framework driver for ASPEED G6 SoC.
> +
> + This driver provides support for ASPEED G6 PWM controllers.
> +
> config PWM_ATMEL
> tristate "Atmel PWM support"
> depends on OF
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index cbdcd55d69ee..29d22d806e68 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -2,6 +2,7 @@
> obj-$(CONFIG_PWM) += core.o
> obj-$(CONFIG_PWM_SYSFS) += sysfs.o
> obj-$(CONFIG_PWM_AB8500) += pwm-ab8500.o
> +obj-$(CONFIG_PWM_ASPEED_G6) += pwm-aspeed-g6.o
> obj-$(CONFIG_PWM_ATMEL) += pwm-atmel.o
> obj-$(CONFIG_PWM_ATMEL_HLCDC_PWM) += pwm-atmel-hlcdc.o
> obj-$(CONFIG_PWM_ATMEL_TCB) += pwm-atmel-tcb.o
> diff --git a/drivers/pwm/pwm-aspeed-g6.c b/drivers/pwm/pwm-aspeed-g6.c
> new file mode 100644
> index 000000000000..f5bb982c21e6
> --- /dev/null
> +++ b/drivers/pwm/pwm-aspeed-g6.c
> @@ -0,0 +1,368 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (C) 2021 ASPEED Technology Inc.
> + *
> + * PWM controller driver for Aspeed ast26xx SoCs.
> + * This drivers doesn't rollback to previous version of aspeed SoCs.

Does that mean it doesn't support earlier versions of the IP?

> + *
> + * The formula of pwm frequency:
> + * PWM frequency = CLK Source / ((DIV_L + 1) * BIT(DIV_H) * (PERIOD + 1))
> + *
> + * The software driver fixes the period to 256, which causes the high-frequency
> + * precision of the PWM to be coarse, in exchange for the fineness of the duty cycle.
> + *
> + * Register usage:
> + * PIN_ENABLE: When it is unset the pwm controller will always output low to the extern.
> + * Use to determin PWM channel enable/disable.

s/determin PWM channel enable.disable/determine if the PWM channel is enabled or disabled/

> + * CLK_ENABLE: When it is unset the pwm controller will reset the duty counter to 0 and
> + * output low to the PIN_ENABLE mux after that the driver can still change the pwm period
> + * and duty and the value will apply when CLK_ENABLE be set again.
> + * Use to determin whether duty_cycle bigger than 0.
> + * PWM_ASPEED_INVERSE: When it is toggled the output value will inverse immediately.
> + *
> + * Limitations:
> + * - When changing both duty cycle and period, we cannot prevent in
> + * software that the output might produce a period with mixed
> + * settings.
> + *
> + * Improvements:
> + * - When changing the duty cycle or period, our pwm controller will not
> + * generate the glitch, the configure will change at next cycle of pwm.
> + * This improvement can disable/enable through PWM_ASPEED_DUTY_SYNC_DISABLE.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/errno.h>
> +#include <linux/delay.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/mfd/syscon.h>
> +#include <linux/module.h>
> +#include <linux/of_platform.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/sysfs.h>
> +#include <linux/reset.h>
> +#include <linux/regmap.h>
> +#include <linux/bitfield.h>
> +#include <linux/slab.h>
> +#include <linux/pwm.h>
> +
> +/* The channel number of Aspeed pwm controller */
> +#define PWM_ASPEED_NR_PWMS 16
> +
> +/* PWM Control Register */
> +#define PWM_ASPEED_CTRL_CH(ch) (((ch * 0x10) + 0x00))

Please put ch in parenthesis.

> +#define PWM_ASPEED_LOAD_SEL_RISING_AS_WDT BIT(19)
> +#define PWM_ASPEED_DUTY_LOAD_AS_WDT_ENABLE BIT(18)
> +#define PWM_ASPEED_DUTY_SYNC_DISABLE BIT(17)
> +#define PWM_ASPEED_CLK_ENABLE BIT(16)
> +#define PWM_ASPEED_LEVEL_OUTPUT BIT(15)
> +#define PWM_ASPEED_INVERSE BIT(14)
> +#define PWM_ASPEED_OPEN_DRAIN_ENABLE BIT(13)
> +#define PWM_ASPEED_PIN_ENABLE BIT(12)
> +#define PWM_ASPEED_CLK_DIV_H GENMASK(11, 8)
> +#define PWM_ASPEED_CLK_DIV_L GENMASK(7, 0)

It would be great if the bit definitions contained the name of the
register. This simplifies verifying that we're using a define for the
expected register.

> +/* PWM Duty Cycle Register */
> +#define PWM_ASPEED_DUTY_CYCLE_CH(ch) (((ch * 0x10) + 0x04))
> +#define PWM_ASPEED_PERIOD GENMASK(31, 24)
> +#define PWM_ASPEED_POINT_AS_WDT GENMASK(23, 16)
> +#define PWM_ASPEED_FALLING_POINT GENMASK(15, 8)
> +#define PWM_ASPEED_RISING_POINT GENMASK(7, 0)
> +
> +/* PWM fixed value */
> +#define PWM_ASPEED_FIXED_PERIOD 0xff
> +
> +struct aspeed_pwm_data {
> + struct pwm_chip chip;
> + struct clk *clk;
> + struct regmap *regmap;
> + struct reset_control *reset;
> +};
> +
> +static inline struct aspeed_pwm_data *
> +aspeed_pwm_chip_to_data(struct pwm_chip *c)
> +{
> + return container_of(c, struct aspeed_pwm_data, chip);
> +}
> +
> +static void aspeed_set_pwm_clk_enable(struct regmap *regmap, u8 pwm_channel,
> + bool enable)

I'd call this function aspeed_pwm_set_clk_enable to use "aspeed_pwm_" as
the common prefix for all functions. Similarly for the other functions.
> +{
> + regmap_update_bits(regmap, PWM_ASPEED_CTRL_CH(pwm_channel),
> + PWM_ASPEED_CLK_ENABLE,
> + enable ? PWM_ASPEED_CLK_ENABLE : 0);

There is only a single caller for this function, I'd recommend to fold
it into this caller.

> +}
> +
> +static u32 apseed_get_pwm_freq(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> + struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
> + unsigned long rate;
> + u32 index = pwm->hwpwm;
> + u32 div_h, div_l, cur_freq, val;
> +
> + rate = clk_get_rate(priv->clk);
> + regmap_read(priv->regmap, PWM_ASPEED_CTRL_CH(index), &val);
> + div_h = FIELD_GET(PWM_ASPEED_CLK_DIV_H, val);
> + div_l = FIELD_GET(PWM_ASPEED_CLK_DIV_L, val);
> +
> + cur_freq = DIV_ROUND_DOWN_ULL(rate, (BIT(div_h) * (div_l + 1) *
> + (PWM_ASPEED_FIXED_PERIOD + 1)));
> + return cur_freq;
> +}
> +
> +static int aspeed_set_pwm_freq(struct pwm_chip *chip, struct pwm_device *pwm,
> + const struct pwm_state *state)
> +{
> + struct device *dev = chip->dev;
> + struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
> + unsigned long rate;
> + u32 div_h, div_l, freq;
> + u32 index = pwm->hwpwm;
> + /* Get the smallest value for div_h */
> + freq = DIV_ROUND_UP_ULL(NSEC_PER_SEC, state->period);
> + rate = clk_get_rate(priv->clk);
> + div_h = DIV_ROUND_DOWN_ULL(rate,
> + ((FIELD_MAX(PWM_ASPEED_CLK_DIV_L) + 1) *
> + freq * (PWM_ASPEED_FIXED_PERIOD + 1)));

Please don't divide by the result of a division.

> + div_h = order_base_2(div_h);
> + if (div_h > 0xf)
> + div_h = 0xf;
> +
> + div_l = DIV_ROUND_DOWN_ULL(rate >> div_h,
> + (freq * (PWM_ASPEED_FIXED_PERIOD + 1)));
> + if (div_l == 0) {
> + dev_err(dev, "Period too small, cannot implement it");
> + return -ERANGE;
> + }
> +
> + div_l -= 1;
> +
> + if (div_l > 255)
> + div_l = 255;
> +
> + dev_dbg(dev, "clk source: %ld div h %x, l : %x\n", rate, div_h, div_l);
> +
> + regmap_update_bits(priv->regmap, PWM_ASPEED_CTRL_CH(index),
> + (PWM_ASPEED_CLK_DIV_H | PWM_ASPEED_CLK_DIV_L),
> + FIELD_PREP(PWM_ASPEED_CLK_DIV_H, div_h) |
> + FIELD_PREP(PWM_ASPEED_CLK_DIV_L, div_l));
> + return 0;
> +}
> +
> +static void aspeed_set_pwm_duty(struct pwm_chip *chip, struct pwm_device *pwm,
> + const struct pwm_state *state)
> +{
> + struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
> + u32 duty_pt;
> + u32 index = pwm->hwpwm;
> + u32 cur_freq;
> + u64 cur_period;
> +
> + cur_freq = apseed_get_pwm_freq(chip, pwm);

s/apseed/aspeed/

cur_freq is the result of a division ...

> + cur_period = DIV_ROUND_DOWN_ULL(NSEC_PER_SEC, cur_freq);

... dividing through such a number loses precision.


> + duty_pt = DIV_ROUND_DOWN_ULL(
> + state->duty_cycle * (PWM_ASPEED_FIXED_PERIOD + 1), cur_period);
> + if (duty_pt == 0) {
> + aspeed_set_pwm_clk_enable(priv->regmap, index, false);
> + } else {
> + if (duty_pt >= (PWM_ASPEED_FIXED_PERIOD + 1))
> + duty_pt = 0;
> + /* When duty_pt = 0 it mean our duty cycle = 100% */

Please put this comment above the code that it explains.

> + regmap_update_bits(
> + priv->regmap, PWM_ASPEED_DUTY_CYCLE_CH(index),
> + PWM_ASPEED_FALLING_POINT,
> + FIELD_PREP(PWM_ASPEED_FALLING_POINT, duty_pt));
> + aspeed_set_pwm_clk_enable(priv->regmap, index, true);
> + }
> +}
> +
> +static void aspeed_set_pwm_polarity(struct pwm_chip *chip,
> + struct pwm_device *pwm,
> + const struct pwm_state *state)
> +{
> + struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
> + u32 index = pwm->hwpwm;
> +
> + regmap_update_bits(priv->regmap, PWM_ASPEED_CTRL_CH(index),
> + PWM_ASPEED_INVERSE,
> + FIELD_PREP(PWM_ASPEED_INVERSE, state->polarity));
> +}

This function also only has a single caller and can better be folded
into it.

> +static void aspeed_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> + struct pwm_state *state)
> +{
> + struct device *dev = chip->dev;
> + struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
> + u32 index = pwm->hwpwm;
> + bool polarity, ch_en, clk_en;
> + u32 duty_pt, val;
> + u32 cur_freq;
> +
> + regmap_read(priv->regmap, PWM_ASPEED_CTRL_CH(index), &val);
> + polarity = FIELD_GET(PWM_ASPEED_INVERSE, val);
> + ch_en = FIELD_GET(PWM_ASPEED_PIN_ENABLE, val);
> + clk_en = FIELD_GET(PWM_ASPEED_CLK_ENABLE, val);
> + regmap_read(priv->regmap, PWM_ASPEED_DUTY_CYCLE_CH(index), &val);
> + duty_pt = FIELD_GET(PWM_ASPEED_FALLING_POINT, val);
> +
> + cur_freq = apseed_get_pwm_freq(chip, pwm);
> +
> + state->period = DIV_ROUND_DOWN_ULL(NSEC_PER_SEC, cur_freq);

Please round up in .get_state().

> + if (clk_en && duty_pt)
> + state->duty_cycle = DIV_ROUND_DOWN_ULL(
> + state->period * duty_pt, PWM_ASPEED_FIXED_PERIOD + 1);
> + else
> + state->duty_cycle = clk_en ? state->period : 0;
> + state->polarity = polarity;
> + state->enabled = ch_en;
> + dev_dbg(dev, "get period: %lldns, duty_cycle: %lldns", state->period,
> + state->duty_cycle);
> +}
> +
> +static int aspeed_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> + const struct pwm_state *state)
> +{
> + struct device *dev = chip->dev;
> + struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
> + u32 index = pwm->hwpwm;
> + struct pwm_state cur_state;
> + int ret;
> +
> + aspeed_pwm_get_state(chip, pwm, &cur_state);
> + dev_dbg(dev, "cur period: %lldns, cur duty_cycle: %lldns",
> + cur_state.period, cur_state.duty_cycle);
> + dev_dbg(dev, "apply period: %lldns, duty_cycle: %lldns", state->period,
> + state->duty_cycle);
> + regmap_update_bits(priv->regmap, PWM_ASPEED_CTRL_CH(index),
> + PWM_ASPEED_PIN_ENABLE,
> + state->enabled ? PWM_ASPEED_PIN_ENABLE : 0);
> + if (cur_state.period != state->period) {
> + ret = aspeed_set_pwm_freq(chip, pwm, state);
> + if (ret)
> + return ret;
> + aspeed_set_pwm_duty(chip, pwm, state);
> + } else if (cur_state.duty_cycle != state->duty_cycle)
> + aspeed_set_pwm_duty(chip, pwm, state);

In aspeed_set_pwm_duty() you call apseed_get_pwm_freq(), in one of the two
cases above you already know the freq. If you ask me, just drop the
cur_state.period != state->period check and calculate all the required
settings unconditionally. Then you also don't need to call
aspeed_pwm_get_state(). (Apart from that apseed_get_pwm_freq implements
the wrong rounding for .apply().)

> + aspeed_set_pwm_polarity(chip, pwm, state);
> + return 0;
> +}
> +
> +static const struct pwm_ops aspeed_pwm_ops = {
> + .apply = aspeed_pwm_apply,
> + .get_state = aspeed_pwm_get_state,
> + .owner = THIS_MODULE,
> +};
> +
> +static int aspeed_pwm_probe(struct platform_device *pdev)
> +{
> + struct device *dev = &pdev->dev;
> + int ret, index;
> + struct aspeed_pwm_data *priv;
> + struct device_node *np;
> +
> + priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> + if (!priv)
> + return -ENOMEM;
> +
> + np = pdev->dev.parent->of_node;
> + if (!of_device_is_compatible(np, "aspeed,ast2600-pwm-tach")) {
> + dev_err(dev, "unsupported pwm device binding\n");
> + return -ENODEV;
> + }
> +
> + priv->regmap = syscon_node_to_regmap(np);
> + if (IS_ERR(priv->regmap)) {
> + dev_err(dev, "Couldn't get regmap\n");
> + return -ENODEV;

Please return PTR_ERR(priv->regmap) here and use dev_err_probe for
consistency.

> + }
> +
> + priv->clk = of_clk_get(np, 0);

Maybe use devm_clk_get() instead? (Otherwise you have to put the clock
in the error paths.)

> + if (IS_ERR(priv->clk))
> + return dev_err_probe(dev, PTR_ERR(priv->clk),
> + "get clock failed\n");
> +
> + ret = clk_prepare_enable(priv->clk);
> + if (ret) {
> + dev_err(dev, "couldn't enable clock\n");
> + return ret;
> + }
> +
> + priv->reset = of_reset_control_get_shared(np, NULL);
> + if (IS_ERR(priv->reset))
> + return dev_err_probe(dev, PTR_ERR(priv->reset),
> + "get reset failed\n");
> +
> + ret = reset_control_deassert(priv->reset);
> + if (ret) {
> + dev_err(dev, "cannot deassert reset control: %pe\n",
> + ERR_PTR(ret));
> + clk_disable_unprepare(priv->clk);

Consider using goto for error handling. Then you don't have to repeat
the same thing over and over again.

> + return ret;
> + }
> +
> + priv->chip.dev = dev;
> + priv->chip.ops = &aspeed_pwm_ops;
> + priv->chip.npwm = PWM_ASPEED_NR_PWMS;
> + priv->chip.of_xlate = of_pwm_xlate_with_flags;
> + priv->chip.of_pwm_n_cells = 3;
> +
> + /*
> + * Fixed the period to the max value and rising point to 0
> + * for high resolution and simplified frequency calculation.

There is a stray non-printable char before "simplified".

> + */
> + for (index = 0; index < PWM_ASPEED_NR_PWMS; index++) {
> + regmap_update_bits(
> + priv->regmap, PWM_ASPEED_DUTY_CYCLE_CH(index),
> + PWM_ASPEED_PERIOD,
> + FIELD_PREP(PWM_ASPEED_PERIOD, PWM_ASPEED_FIXED_PERIOD));
> + regmap_update_bits(priv->regmap,
> + PWM_ASPEED_DUTY_CYCLE_CH(index),
> + PWM_ASPEED_RISING_POINT, 0);
> + }

Please don't modify the output in .probe. .apply is the only function
that is supposed to do that.

> +
> + ret = pwmchip_add(&priv->chip);
> + if (ret < 0) {
> + dev_err(dev, "failed to add PWM chip: %pe\n", ERR_PTR(ret));
> + reset_control_assert(priv->reset);
> + clk_disable_unprepare(priv->clk);
> + return ret;
> + }
> + dev_set_drvdata(dev, priv);
> + return ret;

s/ret/0/

> +}
> +
> +static int aspeed_pwm_remove(struct platform_device *dev)
> +{
> + struct aspeed_pwm_data *priv = platform_get_drvdata(dev);
> +
> + pwmchip_remove(&priv->chip);
> + reset_control_assert(priv->reset);
> + clk_disable_unprepare(priv->clk);
> +
> + return 0;
> +}
> +
> +static const struct of_device_id of_pwm_match_table[] = {
> + {
> + .compatible = "aspeed,ast2600-pwm",
> + },
> + {},
> +};
> +MODULE_DEVICE_TABLE(of, of_pwm_match_table);
> +
> +static struct platform_driver aspeed_pwm_driver = {
> + .probe = aspeed_pwm_probe,
> + .remove = aspeed_pwm_remove,
> + .driver = {
> + .name = "aspeed_pwm",
> + .of_match_table = of_pwm_match_table,
> + },
> +};

Please use alignment of = consistently. Either don't do it at all (my
favourite) or do it for all structs in the same way.

Best regards
Uwe

--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |

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