Re: [v7 2/2] pwm: Add Aspeed ast2600 PWM support

[Uwe Kleine-König]

Hello,

On Tue, May 25, 2021 at 12:32:24PM +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         |   9 +
>  drivers/pwm/Makefile        |   1 +
>  drivers/pwm/pwm-aspeed-g6.c | 334 ++++++++++++++++++++++++++++++++++++

This doesn't match the driver name which is only "aspeed_pwm". Can you
please use matching names and pick the function prefix accordingly? What
is the difference between g6 and ast2600?
My personal preference is using a - in the driver name.

>  3 files changed, 344 insertions(+)
>  create mode 100644 drivers/pwm/pwm-aspeed-g6.c
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 63be5362fd3a..3b2d4cf024a6 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -51,6 +51,15 @@ 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.

You picked the wrong sentence here in reply to my review comment for v5.
Please make this:

	This driver provides support for ASPEED G6 PWM controller.

> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called pwm-aspeed-g6.
> +
>  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..566aff9d7f23
> --- /dev/null
> +++ b/drivers/pwm/pwm-aspeed-g6.c
> @@ -0,0 +1,334 @@
> +// 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 support earlier version of the IP.
> + *
> + * The formula of pwm frequency:
> + * PWM frequency = CLK Source / ((DIV_L + 1) * BIT(DIV_H) * (PERIOD + 1))

Given that PWMs are abstracted using period duration and not frequency,
I suggest to make this:

	period duration = ((DIV_L + 1) * BIT(DIV_H) * (PERIOD + 1)) / input-clk

> + * The software driver fixes the period to 255, 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 determine whether 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.

s/determin/determine/

Unsetting CLK_ENABLE has an immediate effect, right? 

> + * PWM_ASPEED_CTRL_INVERSE: When it is toggled the output value will inverse immediately.
> + * PWM_ASPEED_DUTY_CYCLE_FALLING_POINT/PWM_ASPEED_DUTY_CYCLE_RISING_POINT: When these two
> + * values are equal it means the duty cycle = 100%.

Just for my understanding: These allow to implement a phase offset and
so to implement inverse polarity you can either use
PWM_ASPEED_CTRL_INVERSE or set these values accordingly, right?

> + * Limitations:
> + * - When changing both duty cycle and period, we cannot prevent in
> + *   software that the output might produce a period with mixed
> + *   settings.

 - Disabling the PWM doesn't complete the current period.

> + *
> + * Improvements:
> + * - When changing the duty cycle or period, our pwm controller will not

When only changing one of duty cycle or period, ... ?

> + *   generate the glitch, the configure will change at next cycle of pwm.
> + *   This improvement can disable/enable through PWM_ASPEED_CTRL_DUTY_SYNC_DISABLE.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/errno.h>
> +#include <linux/delay.h>

I think at least this one is not needed.

> +#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>
> +#include <linux/math64.h>
> +
> +/* The channel number of Aspeed pwm controller */

Is there an officially correct spelling of "Aspeed" that your marketing
section would be happy if it were to be used consistently? We have
"Aspeed" and "ASPEED" in this patch set.

> +#define PWM_ASPEED_NR_PWMS 16
> +
> +/* PWM Control Register */
> +#define PWM_ASPEED_CTRL_CH(ch) (((ch)*0x10) + 0x00)

Is "_CH" part of the register name in the manual? If not I suggest to
drop it. Spacing is wrong, there should be one space around the *. Also
you can drop the parenthesis around the multiplication.

> +#define PWM_ASPEED_CTRL_LOAD_SEL_RISING_AS_WDT BIT(19)
> +#define PWM_ASPEED_CTRL_DUTY_LOAD_AS_WDT_ENABLE BIT(18)
> +#define PWM_ASPEED_CTRL_DUTY_SYNC_DISABLE BIT(17)
> +#define PWM_ASPEED_CTRL_CLK_ENABLE BIT(16)
> +#define PWM_ASPEED_CTRL_LEVEL_OUTPUT BIT(15)
> +#define PWM_ASPEED_CTRL_INVERSE BIT(14)
> +#define PWM_ASPEED_CTRL_OPEN_DRAIN_ENABLE BIT(13)
> +#define PWM_ASPEED_CTRL_PIN_ENABLE BIT(12)
> +#define PWM_ASPEED_CTRL_CLK_DIV_H GENMASK(11, 8)
> +#define PWM_ASPEED_CTRL_CLK_DIV_L GENMASK(7, 0)
> +
> +/* PWM Duty Cycle Register */
> +#define PWM_ASPEED_DUTY_CYCLE_CH(ch) (((ch)*0x10) + 0x04)
> +#define PWM_ASPEED_DUTY_CYCLE_PERIOD GENMASK(31, 24)
> +#define PWM_ASPEED_DUTY_CYCLE_POINT_AS_WDT GENMASK(23, 16)
> +#define PWM_ASPEED_DUTY_CYCLE_FALLING_POINT GENMASK(15, 8)
> +#define PWM_ASPEED_DUTY_CYCLE_RISING_POINT GENMASK(7, 0)
> +
> +/* PWM fixed value */
> +#define PWM_ASPEED_FIXED_PERIOD FIELD_MAX(PWM_ASPEED_DUTY_CYCLE_PERIOD)
> +
> +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)

Please rename the parameter to chip for consistency.

> +{
> +	return container_of(c, struct aspeed_pwm_data, chip);
> +}
> +
> +static u64 aspeed_pwm_get_period(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 val;
> +	u64 period, div_h, div_l, clk_period;
> +
> +	rate = clk_get_rate(priv->clk);
> +	regmap_read(priv->regmap, PWM_ASPEED_CTRL_CH(index), &val);
> +	div_h = FIELD_GET(PWM_ASPEED_CTRL_CLK_DIV_H, val);
> +	div_l = FIELD_GET(PWM_ASPEED_CTRL_CLK_DIV_L, val);
> +	regmap_read(priv->regmap, PWM_ASPEED_DUTY_CYCLE_CH(index), &val);
> +	clk_period = FIELD_GET(PWM_ASPEED_DUTY_CYCLE_PERIOD, val);
> +	period = DIV_ROUND_UP_ULL((u64)NSEC_PER_SEC * _BITULL(div_h) *
> +					  (div_l + 1) * (clk_period + 1),
> +				  rate);
> +
> +	return period;
> +}
> +
> +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;
> +
> +	regmap_read(priv->regmap, PWM_ASPEED_CTRL_CH(index), &val);
> +	polarity = FIELD_GET(PWM_ASPEED_CTRL_INVERSE, val);
> +	ch_en = FIELD_GET(PWM_ASPEED_CTRL_PIN_ENABLE, val);
> +	clk_en = FIELD_GET(PWM_ASPEED_CTRL_CLK_ENABLE, val);
> +	regmap_read(priv->regmap, PWM_ASPEED_DUTY_CYCLE_CH(index), &val);
> +	duty_pt = FIELD_GET(PWM_ASPEED_DUTY_CYCLE_FALLING_POINT, val);
> +
> +	state->period = aspeed_pwm_get_period(chip, pwm);

In aspeed_pwm_get_period() you needlessly read PWM_ASPEED_CTRL_CH once
more. If you unroll the call you can get rid of that.

> +	if (clk_en && duty_pt)
> +		state->duty_cycle = DIV_ROUND_UP_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, duty_pt;
> +	unsigned long rate;
> +	u64 apply_period, div_h, div_l, divisor;
> +
> +	dev_dbg(dev, "expect period: %lldns, duty_cycle: %lldns", state->period,
> +		state->duty_cycle);
> +
> +	rate = clk_get_rate(priv->clk);
> +	/*
> +	 * Pick the smallest value for div_h so that div_l can be the biggest
> +	 * which results in a finer resolution near the target period value.
> +	 */
> +	divisor = (u64)NSEC_PER_SEC * (PWM_ASPEED_FIXED_PERIOD + 1) *
> +		  (FIELD_MAX(PWM_ASPEED_CTRL_CLK_DIV_L) + 1);
> +	div_h = order_base_2(DIV64_U64_ROUND_UP(rate * state->period, divisor));
> +	if (div_h > 0xf)
> +		div_h = 0xf;
> +
> +	divisor = ((u64)NSEC_PER_SEC * (PWM_ASPEED_FIXED_PERIOD + 1)) << div_h;
> +	div_l = div64_u64(rate * state->period, divisor);
> +
> +	if (div_l == 0)
> +		return -ERANGE;
> +
> +	div_l -= 1;
> +
> +	if (div_l > 255)
> +		div_l = 255;
> +
> +	dev_dbg(dev, "clk source: %ld div_h %lld, div_l : %lld\n", rate, div_h,
> +		div_l);
> +
> +	apply_period = DIV_ROUND_UP_ULL((u64)NSEC_PER_SEC * _BITULL(div_h) *
> +						(div_l + 1) *
> +						(PWM_ASPEED_FIXED_PERIOD + 1),
> +					rate);
> +	duty_pt = DIV_ROUND_DOWN_ULL(state->duty_cycle *
> +					     (PWM_ASPEED_FIXED_PERIOD + 1),
> +				     apply_period);

Don't divide by the result of a division. So better use:

	state->duty_cycle * rate
	----------------------------------------
	NSEC_PER_SEC * BITULL(div_h) * div_l + 1

(Is it correct that PWM_ASPEED_FIXED_PERIOD doesn't appear here?)

> +	dev_dbg(dev, "apply_period = %lld, duty_cycle = %lld, duty_pt = %d\n",
> +		apply_period, state->duty_cycle, duty_pt);
> +
> +	/*
> +	 * Fixed the period to the max value and rising point to 0
> +	 * for high resolution and simplify frequency calculation.

I'd write here:

	Fixed DUTY_CYCLE_PERIOD to its max value to get a fine grained
	resolution for duty_cycle at the expense of a coarser period
	resolution.

using rising point = 0 is needed for correctness (IIUC) to have the
period start with the active part, so this doesn't need mentioning here.

> +	 */
> +	regmap_update_bits(priv->regmap, PWM_ASPEED_DUTY_CYCLE_CH(index),
> +			   (PWM_ASPEED_DUTY_CYCLE_PERIOD |
> +			    PWM_ASPEED_DUTY_CYCLE_RISING_POINT),

No need to use parenthesis here.

> +			   FIELD_PREP(PWM_ASPEED_DUTY_CYCLE_PERIOD,
> +				      PWM_ASPEED_FIXED_PERIOD));
> +
> +	regmap_update_bits(priv->regmap, PWM_ASPEED_CTRL_CH(index),
> +			   PWM_ASPEED_CTRL_PIN_ENABLE,
> +			   state->enabled ? PWM_ASPEED_CTRL_PIN_ENABLE : 0);

If PIN_ENABLE is unset the output is low anyhow, so make this first if
state->enabled = false and exit early. This way you don't introduce a
glitch by earlier register accesses and save some time by not
calculating and writing register values that don't have an effect
anyhow.

> +	regmap_update_bits(
> +		priv->regmap, PWM_ASPEED_CTRL_CH(index),

Wrong indention. Continuation lines are supposed to be aligned to the
opening (.

> +		(PWM_ASPEED_CTRL_CLK_DIV_H | PWM_ASPEED_CTRL_CLK_DIV_L),

unneeded parenthesis once more.

> +		FIELD_PREP(PWM_ASPEED_CTRL_CLK_DIV_H, div_h) |
> +			FIELD_PREP(PWM_ASPEED_CTRL_CLK_DIV_L, div_l));
> +
> +	if (duty_pt == 0) {
> +		regmap_update_bits(priv->regmap, PWM_ASPEED_CTRL_CH(index),
> +				   PWM_ASPEED_CTRL_CLK_ENABLE, 0);

This register write can be better combined with the previous write to
the same register?! Below is a third access to this register.

> +	} else {
> +		if (duty_pt >= (PWM_ASPEED_FIXED_PERIOD + 1))
> +			duty_pt = 0;
> +		regmap_update_bits(
> +			priv->regmap, PWM_ASPEED_DUTY_CYCLE_CH(index),
> +			PWM_ASPEED_DUTY_CYCLE_FALLING_POINT,
> +			FIELD_PREP(PWM_ASPEED_DUTY_CYCLE_FALLING_POINT,
> +				   duty_pt));
> +		regmap_update_bits(priv->regmap, PWM_ASPEED_CTRL_CH(index),
> +				   PWM_ASPEED_CTRL_CLK_ENABLE,
> +				   PWM_ASPEED_CTRL_CLK_ENABLE);
> +	}
> +
> +	regmap_update_bits(priv->regmap, PWM_ASPEED_CTRL_CH(index),
> +			   PWM_ASPEED_CTRL_INVERSE,
> +			   FIELD_PREP(PWM_ASPEED_CTRL_INVERSE,
> +				      state->polarity));
> +	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;
> +	struct aspeed_pwm_data *priv;
> +	struct device_node *np;
> +	struct platform_device *parent_dev;
> +
> +	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"))
> +		return dev_err_probe(dev, -ENODEV,
> +				     "unsupported pwm device binding\n");
> +
> +	priv->regmap = syscon_node_to_regmap(np);
> +	if (IS_ERR(priv->regmap))
> +		return dev_err_probe(dev, PTR_ERR(priv->regmap),
> +				     "couldn't get regmap\n");
> +
> +	parent_dev = of_find_device_by_node(np);
> +	priv->clk = devm_clk_get(&parent_dev->dev, 0);
> +	if (IS_ERR(priv->clk))
> +		return dev_err_probe(dev, PTR_ERR(priv->clk),
> +				     "couldn't get clock\n");
> +
> +	ret = clk_prepare_enable(priv->clk);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "couldn't enable clock\n");
> +
> +	priv->reset = of_reset_control_get_shared(np, NULL);

Better use devm_reset_control_get_shared(). Otherwise you have to make
use of reset_control_put() in the error path and in .remove().

> +	if (IS_ERR(priv->reset))

You have to disable (and unprepare) the clock here.

> +		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));

dev_err_probe(dev, ret, "cannot ...

for consistency please.

> +		goto err_disable_clk;
> +	}
> +
> +	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;

The last two shouldn't be necessary. See commit
e9fdf122cf3442573d811c0cb664d6b5c30b7780.

> +	ret = pwmchip_add(&priv->chip);
> +	if (ret < 0) {
> +		dev_err(dev, "failed to add PWM chip: %pe\n", ERR_PTR(ret));
> +		goto err_assert_reset;
> +	}
> +	dev_set_drvdata(dev, priv);
> +	return 0;
> +err_assert_reset:
> +	reset_control_assert(priv->reset);
> +err_disable_clk:
> +	clk_disable_unprepare(priv->clk);
> +	return ret;
> +}
> +
> +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,
> +	},
> +};
> +
> +module_platform_driver(aspeed_pwm_driver);
> +
> +MODULE_AUTHOR("Billy Tsai <billy_tsai@xxxxxxxxxxxxxx>");
> +MODULE_DESCRIPTION("ASPEED PWM device driver");

Maybe mention ast2600 here, too? Or g6?

> +MODULE_LICENSE("GPL v2");

Best regards
Uwe

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

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