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Subject: Re: [PATCH v2 2/2] Add PWM fan controller driver for LGM SoC
To:     =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= <u.kleine-koenig@pengutronix.de>
Cc:     linux-pwm@vger.kernel.org, thierry.reding@gmail.com,
        p.zabel@pengutronix.de, robh+dt@kernel.org,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        andriy.shevchenko@intel.com, songjun.Wu@intel.com,
        cheol.yong.kim@intel.com, qi-ming.wu@intel.com,
        rahul.tanwar.linux@gmail.com
References: <cover.1592474693.git.rahul.tanwar@linux.intel.com>
 <79fefda4aad5ebeb368129375bf128b74ed12224.1592474693.git.rahul.tanwar@linux.intel.com>
 <20200619060213.ldvun5y4tgnz55hh@taurus.defre.kleine-koenig.org>
From:   "Tanwar, Rahul" <rahul.tanwar@linux.intel.com>
Message-ID: <97273851-dd58-ea02-2393-bdb1e77e1a50@linux.intel.com>
Date:   Thu, 25 Jun 2020 15:28:38 +0800
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Hi Uwe,

Thanks for your valuable feedback.

On 19/6/2020 2:02 pm, Uwe Kleine-K?nig wrote:
> Hello Rahul,
>
> On Thu, Jun 18, 2020 at 08:05:13PM +0800, Rahul Tanwar wrote:
>> Intel Lightning Mountain(LGM) SoC contains a PWM fan controller.
>> This PWM controller does not have any other consumer, it is a
>> dedicated PWM controller for fan attached to the system. Add
>> driver for this PWM fan controller.
>>
>> Signed-off-by: Rahul Tanwar <rahul.tanwar@linux.intel.com>
>> ---
>>  drivers/pwm/Kconfig         |   9 +
>>  drivers/pwm/Makefile        |   1 +
>>  drivers/pwm/pwm-intel-lgm.c | 400 ++++++++++++++++++++++++++++++++++++++++++++
>>  3 files changed, 410 insertions(+)
>>  create mode 100644 drivers/pwm/pwm-intel-lgm.c
>>
>> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
>> index cb8d739067d2..a3303e22d5fa 100644
>> --- a/drivers/pwm/Kconfig
>> +++ b/drivers/pwm/Kconfig
>> @@ -232,6 +232,15 @@ config PWM_IMX_TPM
>>  	  To compile this driver as a module, choose M here: the module
>>  	  will be called pwm-imx-tpm.
>>  
>> +config PWM_INTEL_LGM
>> +	tristate "Intel LGM PWM support"
>> +	depends on X86 || COMPILE_TEST
>> +	help
>> +	  Generic PWM fan controller driver for LGM SoC.
>> +
>> +	  To compile this driver as a module, choose M here: the module
>> +	  will be called pwm-intel-lgm.
>> +
>>  config PWM_IQS620A
>>  	tristate "Azoteq IQS620A PWM support"
>>  	depends on MFD_IQS62X || COMPILE_TEST
>> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
>> index a59c710e98c7..db154a6b4f51 100644
>> --- a/drivers/pwm/Makefile
>> +++ b/drivers/pwm/Makefile
>> @@ -20,6 +20,7 @@ obj-$(CONFIG_PWM_IMG)		+= pwm-img.o
>>  obj-$(CONFIG_PWM_IMX1)		+= pwm-imx1.o
>>  obj-$(CONFIG_PWM_IMX27)		+= pwm-imx27.o
>>  obj-$(CONFIG_PWM_IMX_TPM)	+= pwm-imx-tpm.o
>> +obj-$(CONFIG_PWM_INTEL_LGM)	+= pwm-intel-lgm.o
>>  obj-$(CONFIG_PWM_IQS620A)	+= pwm-iqs620a.o
>>  obj-$(CONFIG_PWM_JZ4740)	+= pwm-jz4740.o
>>  obj-$(CONFIG_PWM_LP3943)	+= pwm-lp3943.o
>> diff --git a/drivers/pwm/pwm-intel-lgm.c b/drivers/pwm/pwm-intel-lgm.c
>> new file mode 100644
>> index 000000000000..3c7077acb161
>> --- /dev/null
>> +++ b/drivers/pwm/pwm-intel-lgm.c
>> @@ -0,0 +1,400 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (C) 2020 Intel Corporation.
>> + *
>> + * Notes & Limitations:
>> + * - The hardware supports fixed period which is dependent on 2/3 or 4
>> + *   wire fan mode.
>> + * - Supports normal polarity. Does not support changing polarity.
>> + * - When PWM is disabled, output of PWM will become 0(inactive). It doesn't
>> + *   keep track of running period.
>> + * - When duty cycle is changed, PWM output may be a mix of previous setting
>> + *   and new setting for the first period. From second period, the output is
>> + *   based on new setting.
>> + * - Supports 100% duty cycle.
>> + * - It is a dedicated PWM fan controller. There are no other consumers for
>> + *   this PWM controller.
>> + */
>> +#include <linux/bitfield.h>
>> +#include <linux/clk.h>
>> +#include <linux/module.h>
>> +#include <linux/of_device.h>
>> +#include <linux/pwm.h>
>> +#include <linux/regmap.h>
>> +#include <linux/reset.h>
>> +
>> +#define PWM_FAN_CON0		0x0
>> +#define PWM_FAN_EN_EN		BIT(0)
>> +#define PWM_FAN_EN_DIS		0x0
>> +#define PWM_FAN_EN_MSK		BIT(0)
>> +#define PWM_FAN_MODE_2WIRE	0x0
>> +#define PWM_FAN_MODE_4WIRE	0x1
>> +#define PWM_FAN_MODE_MSK	BIT(1)
>> +#define PWM_FAN_PWM_DIS_DIS	0x0
>> +#define PWM_FAN_PWM_DIS_MSK	BIT(2)
>> +#define PWM_TACH_EN_EN		0x1
>> +#define PWM_TACH_EN_MSK		BIT(4)
>> +#define PWM_TACH_PLUS_2		0x0
>> +#define PWM_TACH_PLUS_4		0x1
>> +#define PWM_TACH_PLUS_MSK	BIT(5)
>> +#define PWM_FAN_DC_MSK		GENMASK(23, 16)
>> +
>> +#define PWM_FAN_CON1		0x4
>> +#define PWM_FAN_MAX_RPM_MSK	GENMASK(15, 0)
>> +
>> +#define PWM_FAN_STAT		0x10
>> +#define PWM_FAN_TACH_MASK	GENMASK(15, 0)
>> +
>> +#define MAX_RPM			(BIT(16) - 1)
>> +#define DFAULT_RPM		4000
>> +#define MAX_DUTY_CYCLE		(BIT(8) - 1)
>> +
>> +#define FRAC_BITS		10
>> +#define DC_BITS			8
>> +#define TWO_TENTH		204
>> +
>> +#define PERIOD_2WIRE_NSECS	40000000
>> +#define PERIOD_4WIRE_NSECS	40000
>> +
>> +#define TWO_SECONDS		2000
>> +#define IGNORE_FIRST_ERR	1
>> +#define THIRTY_SECS_WINDOW	15
>> +#define ERR_CNT_THRESHOLD	6
>> +
>> +struct lgm_pwm_chip {
>> +	struct pwm_chip chip;
>> +	struct regmap *regmap;
>> +	struct clk *clk;
>> +	struct reset_control *rst;
>> +	u32 tach_en;
>> +	u32 max_rpm;
>> +	u32 set_rpm;
>> +	u32 set_dc;
>> +	u32 period;
>> +	struct delayed_work work;
>> +};
>> +
>> +static inline struct lgm_pwm_chip *to_lgm_pwm_chip(struct pwm_chip *chip)
>> +{
>> +	return container_of(chip, struct lgm_pwm_chip, chip);
>> +}
>> +
>> +static int lgm_pwm_update_dc(struct lgm_pwm_chip *pc, u32 val)
>> +{
>> +	return regmap_update_bits(pc->regmap, PWM_FAN_CON0, PWM_FAN_DC_MSK,
>> +				  FIELD_PREP(PWM_FAN_DC_MSK, val));
>> +}
>> +
>> +static int lgm_pwm_enable(struct pwm_chip *chip, bool enable)
>> +{
>> +	struct lgm_pwm_chip *pc = to_lgm_pwm_chip(chip);
>> +	struct regmap *regmap = pc->regmap;
>> +
>> +	if (enable) {
>> +		regmap_update_bits(regmap, PWM_FAN_CON0,
>> +				   PWM_FAN_EN_MSK, PWM_FAN_EN_EN);
>> +		if (pc->tach_en)
>> +			schedule_delayed_work(&pc->work, msecs_to_jiffies(10000));
>> +	} else {
>> +		if (pc->tach_en)
>> +			cancel_delayed_work_sync(&pc->work);
>> +		regmap_update_bits(regmap, PWM_FAN_CON0,
>> +			   	   PWM_FAN_EN_MSK, PWM_FAN_EN_DIS);
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int lgm_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>> +			 const struct pwm_state *state)
>> +{
>> +	struct lgm_pwm_chip *pc = to_lgm_pwm_chip(chip);
>> +	struct pwm_state cur_state;
>> +	u32 duty_cycle, duty, val;
>> +	int ret = 0;
>> +
>> +	if (state->polarity != PWM_POLARITY_NORMAL ||
>> +	    state->period != pc->period)
> The period-check is too strict, please accept periods bigger than the
> resulting value. This case however isn't handled correctly yet in the
> following code and needs:
>
> 	period = min(state->period, pc->period);
>
> 	if (state->polarity != PWM_POLARITY_NORMAL ||
> 	    period < pc->period)
> 	    	return -EINVAL;
>
> (and then use period instead of state->period in the following)
>
>> +		return -EINVAL;
>> +
>> +	cur_state = pwm->state;
>> +	duty_cycle = state->duty_cycle;
> This would then be:
>
> 	duty_cycle = min(state->duty_cycle, period);
>
>> +	if (!state->enabled)
>> +		duty_cycle = 0;
> What happens if you don't set duty_cycle to 0? Is it just to prevent a
> spike in lgm_pwm_update_dc before calling lgm_pwm_enable(.., false)? If
> so, what about skipping writing (and calculating) the duty register
> value at all?

Thanks, will update. Agree that setting duty_cycle to 0 is redundant.
Setting duty_cycle to 0 is equivalent to disabling PWM. Will remove it.

>> +	duty = duty_cycle * (1U << DC_BITS);
>> +	val = DIV_ROUND_CLOSEST(duty, state->period);
> This is equivalent to:
>
> 	val = DIV_ROUND_CLOSEST(duty_cycle << DC_BITS, state->period);
>
> which doesn't need two variables with similar name but different
> scaling. Having said that using closest rounding is wrong here, please
> round down.

Unable to find a 32 bit variant of DIV_ROUND_DOWN API unlike
DIV_ROUND_UP. Do you have any suggestion for such a API? If not,
i will add one new API for this purpose in the driver.

>> +	val = min_t(u32, val, MAX_DUTY_CYCLE);
> Hmm, this looks suspicious. Does the hardware really produce 100% when
> val = MAX_DUTY_CYCLE? Either it doesn't or there is a rounding error in
> your algorithm. Does the PWM support 0%? It would help to mention the
> formula from the reference manual to verify and understand your
> algorithm. Please add a comment for that.

Yes, hardware claims to produce 100% when val = 0xff for 8 bit duty cycle
register field. But it doesn't support 0%. Minimum supported is 20%.
Sorry i am unable to figure out your point here. Can you please elaborate
more? I was just trying to ensure that reg value doesn't exceed max value
of 0xff.

>> +	if (pc->tach_en) {
>> +		pc->set_dc = val;
>> +		pc->set_rpm = val * pc->max_rpm / MAX_DUTY_CYCLE;
>> +	}
>> +
>> +	ret = lgm_pwm_update_dc(pc, val);
>> +
>> +	if (state->enabled != cur_state.enabled)
>> +		lgm_pwm_enable(chip, state->enabled);
> I would prefer if you would make this call conditional on the (cached)
> state of the PWM_FAN_EN_MSK bit instead of pwm->state. This way the
> driver is more independent from pwm API internals.

Well noted.

>> +	return ret;
>> +}
>> +
>> +static void lgm_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
>> +			      struct pwm_state *state)
>> +{
>> +	struct lgm_pwm_chip *pc = to_lgm_pwm_chip(chip);
>> +	u32 duty, val;
>> +
>> +	state->enabled = regmap_test_bits(pc->regmap, PWM_FAN_CON0,
>> +					  PWM_FAN_EN_EN);
>> +	state->polarity = PWM_POLARITY_NORMAL;
>> +	state->period = pc->period; /* fixed period */
>> +
>> +	regmap_read(pc->regmap, PWM_FAN_CON0, &val);
>> +	duty = FIELD_GET(PWM_FAN_DC_MSK, val);
>> +	state->duty_cycle = duty * pc->period >> DC_BITS;
> The rounding here must use the inverse rounding of .apply(). So please
> round up here.

Well noted.

>> +}
>> +
>> +static const struct pwm_ops lgm_pwm_ops = {
>> +	.get_state = lgm_pwm_get_state,
>> +	.apply = lgm_pwm_apply,
>> +	.owner = THIS_MODULE,
>> +};
>> +
>> +static void lgm_pwm_tach_work(struct work_struct *work)
>> +{
>> +	struct lgm_pwm_chip *pc = container_of(work, struct lgm_pwm_chip,
>> +						 work.work);
>> +	struct regmap *regmap = pc->regmap;
>> +	u32 fan_tach, fan_dc, val;
>> +	s32 diff;
>> +	static u32 fanspeed_err_cnt, time_window, delta_dc;
>> +
>> +	/*
>> +	 * Fan speed is tracked by reading the active duty cycle of PWM output
>> +	 * from the active duty cycle register. Some variance in the duty cycle
>> +	 * register value is expected. So we set a time window of 30 seconds and
>> +	 * if we detect inaccurate fan speed 6 times within 30 seconds then we
>> +	 * mark it as fan speed problem and fix it by readjusting the duty cycle.
>> +	 */
>> +
>> +	if (fanspeed_err_cnt > IGNORE_FIRST_ERR)
>> +		/*
>> +		 * Ignore first time we detect inaccurate fan speed
>> +		 * because it is expected during bootup.
>> +		 */
>> +		time_window++;
>> +
>> +	if (time_window == THIRTY_SECS_WINDOW) {
>> +		/*
>> +		 * This work is scheduled every 2 seconds i.e. each time_window
>> +		 * counter step roughly mean 2 seconds. When the time window
>> +		 * reaches 30 seconds, reset all the counters/logic.
>> +		 */
>> +		fanspeed_err_cnt = 0;
>> +		delta_dc = 0;
>> +		time_window = 0;
>> +	}
>> +
>> +	regmap_read(regmap, PWM_FAN_STAT, &fan_tach);
>> +	fan_tach &= PWM_FAN_TACH_MASK;
>> +	if (!fan_tach)
>> +		goto restart_work;
>> +
>> +	val = DIV_ROUND_CLOSEST(pc->set_rpm << FRAC_BITS, fan_tach);
>> +	diff = val - BIT(FRAC_BITS);
>> +
>> +	if (abs(diff) > TWO_TENTH) {
>> +		/* if duty cycle diff is more than two tenth, detect it as error */
>> +		if (fanspeed_err_cnt > IGNORE_FIRST_ERR)
>> +			delta_dc += val;
>> +		fanspeed_err_cnt++;
>> +	}
>> +
>> +	if (fanspeed_err_cnt == ERR_CNT_THRESHOLD) {
>> +		/*
>> +		 * We detected fan speed errors 6 times with 30 seconds.
>> +		 * Fix the error by readjusting duty cycle and reset
>> +		 * our counters/logic.
>> +		 */
>> +		fan_dc = pc->set_dc * delta_dc >> (FRAC_BITS + 2);
>> +		fan_dc = min_t(u32, fan_dc, MAX_DUTY_CYCLE);
>> +		lgm_pwm_update_dc(pc, fan_dc);
>> +		fanspeed_err_cnt = 0;
>> +		delta_dc = 0;
>> +		time_window = 0;
>> +	}
>> +
>> +restart_work:
>> +	/*
>> +	 * Fan speed doesn't need continous tracking. Schedule this work
>> +	 * every two seconds so it doesn't steal too much cpu cycles.
>> +	 */
>> +	schedule_delayed_work(&pc->work, msecs_to_jiffies(TWO_SECONDS));
> You had concerns about my review feedback that I don't like the fan
> stuff in the PWM driver. I still think that the fan part doesn't belong
> here.

We have decided to remove this fan calibration task after concluding that
the same can be achieved by a user space application using sysfs. Will remove
it in v3.

>> +}
>> +
>> +static void lgm_pwm_init(struct lgm_pwm_chip *pc)
>> +{
>> +	struct device *dev = pc->chip.dev;
>> +	struct regmap *regmap = pc->regmap;
>> +	u32 max_rpm, fan_wire, tach_plus, con0_val, con0_mask;
>> +
>> +	if (device_property_read_u32(dev, "intel,fan-wire", &fan_wire))
>> +		fan_wire = 2; /* default is 2 wire mode */
>> +
>> +	con0_val = FIELD_PREP(PWM_FAN_PWM_DIS_MSK, PWM_FAN_PWM_DIS_DIS);
>> +	con0_mask = PWM_FAN_PWM_DIS_MSK | PWM_FAN_MODE_MSK;
> Please don't disable the PWM in .probe()

Well noted.

>> +
>> +	switch (fan_wire) {
>> +	case 4:
>> +		con0_val |= FIELD_PREP(PWM_FAN_MODE_MSK, PWM_FAN_MODE_4WIRE) |
>> +			    FIELD_PREP(PWM_TACH_EN_MSK, PWM_TACH_EN_EN);
>> +		con0_mask |= PWM_TACH_EN_MSK | PWM_TACH_PLUS_MSK;
>> +		pc->tach_en = 1;
>> +		pc->period = PERIOD_4WIRE_NSECS;
>> +		break;
>> +	default:
>> +		/* default is 2wire mode */
>> +		con0_val |= FIELD_PREP(PWM_FAN_MODE_MSK, PWM_FAN_MODE_2WIRE);
>> +		pc->period = PERIOD_2WIRE_NSECS;
>> +		break;
>> +	}
>> +
>> +	if (pc->tach_en) {
>> +		if (device_property_read_u32(dev, "intel,tach-plus",
>> +					     &tach_plus))
>> +			tach_plus = 2;
>> +
>> +		switch (tach_plus) {
>> +		case 4:
>> +			con0_val |= FIELD_PREP(PWM_TACH_PLUS_MSK,
>> +					       PWM_TACH_PLUS_4);
>> +			break;
>> +		default:
>> +			con0_val |= FIELD_PREP(PWM_TACH_PLUS_MSK,
>> +					       PWM_TACH_PLUS_2);
>> +			break;
>> +		}
>> +
>> +		if (device_property_read_u32(dev, "intel,max-rpm", &max_rpm))
>> +			max_rpm = DFAULT_RPM;
>> +
>> +		max_rpm = min_t(u32, max_rpm, MAX_RPM);
>> +		if (max_rpm == 0)
>> +			max_rpm = DFAULT_RPM;
>> +
>> +		pc->max_rpm = max_rpm;
>> +		INIT_DEFERRABLE_WORK(&pc->work, lgm_pwm_tach_work);
>> +		regmap_update_bits(regmap, PWM_FAN_CON1,
>> +				   PWM_FAN_MAX_RPM_MSK, max_rpm);
>> +	}
>> +
>> +	regmap_update_bits(regmap, PWM_FAN_CON0, con0_mask, con0_val);
>> +}
>> +
>> +static const struct regmap_config pwm_regmap_config = {
> Here you missed to add the lgm_ prefix.
>
>> +	.reg_bits = 32,
>> +	.reg_stride = 4,
>> +	.val_bits = 32,
>> +};
>> +
>> +static int lgm_pwm_probe(struct platform_device *pdev)
>> +{
>> +	struct lgm_pwm_chip *pc;
>> +	struct device *dev = &pdev->dev;
>> +	void __iomem *io_base;
>> +	int ret;
>> +
>> +	pc = devm_kzalloc(dev, sizeof(*pc), GFP_KERNEL);
>> +	if (!pc)
>> +		return -ENOMEM;
>> +
>> +	io_base = devm_platform_ioremap_resource(pdev, 0);
>> +	if (IS_ERR(io_base))
>> +		return PTR_ERR(io_base);
>> +
>> +	pc->regmap = devm_regmap_init_mmio(dev, io_base, &pwm_regmap_config);
>> +	if (IS_ERR(pc->regmap)) {
>> +		ret = PTR_ERR(pc->regmap);
>> +		dev_err(dev, "failed to init register map: %pe\n", pc->regmap);
>> +		return ret;
>> +	}
>> +
>> +	pc->clk = devm_clk_get(dev, NULL);
>> +	if (IS_ERR(pc->clk)) {
>> +		ret = PTR_ERR(pc->clk);
>> +		dev_err(dev, "failed to get clock: %pe\n", pc->clk);
>> +		return ret;
>> +	}
>> +
>> +	pc->rst = devm_reset_control_get(dev, NULL);
>> +	if (IS_ERR(pc->rst)) {
>> +		ret = PTR_ERR(pc->rst);
>> +		dev_err(dev, "failed to get reset control: %pe\n", pc->rst);
>> +		return ret;
>> +	}
>> +
>> +	ret = reset_control_deassert(pc->rst);
>> +	if (ret) {
>> +		dev_err(dev, "cannot deassert reset control: %pe\n",
>> +			ERR_PTR(ret));
>> +		return ret;
>> +	}
>> +
>> +	ret = clk_prepare_enable(pc->clk);
>> +	if (ret) {
>> +		dev_err(dev, "failed to enable clock\n");
>> +		return ret;
>> +	}
>> +
>> +	pc->chip.dev = dev;
>> +	pc->chip.ops = &lgm_pwm_ops;
>> +	pc->chip.npwm = 1;
>> +
>> +	lgm_pwm_init(pc);
>> +
>> +	ret = pwmchip_add(&pc->chip);
>> +	if (ret < 0) {
>> +		dev_err(dev, "failed to add PWM chip: %d\n", ret);
> %pe please.

Well noted. Thanks.

Regards,
Rahul