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[v10,1/3] pwm: driver for qualcomm ipq6018 pwm block

Message ID ab2a4c345844f66aa22a847e522b2f4ee0786d8b.1639499239.git.baruch@tkos.co.il (mailing list archive)
State New, archived
Headers show
Series [v10,1/3] pwm: driver for qualcomm ipq6018 pwm block | expand

Commit Message

Baruch Siach Dec. 14, 2021, 4:27 p.m. UTC
From: Baruch Siach <baruch.siach@siklu.com>

Driver for the PWM block in Qualcomm IPQ6018 line of SoCs. Based on
driver from downstream Codeaurora kernel tree. Removed support for older
(V1) variants because I have no access to that hardware.

Tested on IPQ6010 based hardware.

Signed-off-by: Baruch Siach <baruch.siach@siklu.com>
---
v10:

  Restore round up in pwm_div calculation; otherwise diff is always <=
  0, so only bingo match works

  Don't overwrite min_diff on every loop iteration

v9:

Address comment from Uwe Kleine-König:

  Use period_ns*rate in dividers calculation for better accuracy

  Round down pre_div and pwm_div

  Add a comment explaining why pwm_div can't underflow

  Add a comment explaining why pre_div > pwm_div end the search loop

  Drop 'CFG_' from register macros

  Rename to_ipq_pwm_chip() to ipq_pwm_from_chip()

  Change bare 'unsigned' to 'unsigned int'

  Clarify the comment on separate REG1 write for enable/disable

  Round up the period value in .get_state

  Use direct readl/writel so no need to check for regmap errors

v7:

  Change 'offset' to 'reg' for the tcsr offset (Rob)

  Drop clock name; there is only one clock (Bjorn)

  Simplify probe failure code path (Bjorn)

v6:

Address Uwe Kleine-König review comments:

  Drop IPQ_PWM_MAX_DEVICES

  Rely on assigned-clock-rates; drop IPQ_PWM_CLK_SRC_FREQ

  Simplify register offset calculation

  Calculate duty cycle more precisely

  Refuse to set inverted polarity

  Drop redundant IPQ_PWM_REG1_ENABLE bit clear

  Remove x1000 factor in pwm_div calculation, use rate directly, and round up

  Choose initial pre_div such that pwm_div < IPQ_PWM_MAX_DIV

  Ensure pre_div <= pwm_div

  Rename close_ to best_

  Explain in comment why effective_div doesn't overflow

  Limit pwm_div to IPQ_PWM_MAX_DIV - 1 to allow 100% duty cycle

  Disable clock only after pwmchip_remove()

  const pwm_ops

Other changes:

  Add missing linux/bitfield.h header include (kernel test robot)

  Adjust code for PWM device node under TCSR (Rob Herring)

v5:

Use &tcsr_q6 syscon to access registers (Bjorn Andersson)

Address Uwe Kleine-König review comments:

  Implement .get_state()

  Add IPQ_PWM_ prefix to local macros

  Use GENMASK/BIT/FIELD_PREP for register fields access

  Make type of config_div_and_duty() parameters consistent

  Derive IPQ_PWM_MIN_PERIOD_NS from IPQ_PWM_CLK_SRC_FREQ

  Integrate enable/disable into config_div_and_duty() to save register read,
  and reduce frequency glitch on update

  Use min() instead of min_t()

  Fix comment format

  Use dev_err_probe() to indicate probe step failure

  Add missing clk_disable_unprepare() in .remove

  Don't set .owner

v4:

  Use div64_u64() to fix link for 32-bit targets ((kernel test robot
  <lkp@intel.com>, Uwe Kleine-König)

v3:

  s/qcom,pwm-ipq6018/qcom,ipq6018-pwm/ (Rob Herring)

  Fix integer overflow on 32-bit targets (kernel test robot <lkp@intel.com>)

v2:

Address Uwe Kleine-König review comments:

  Fix period calculation when out of range

  Don't set period larger than requested

  Remove PWM disable on configuration change

  Implement .apply instead of non-atomic .config/.enable/.disable

  Don't modify PWM on .request/.free

  Check pwm_div underflow

  Fix various code and comment formatting issues

Other changes:

  Use u64 divisor safe division

  Remove now empty .request/.free
---
 drivers/pwm/Kconfig   |  12 ++
 drivers/pwm/Makefile  |   1 +
 drivers/pwm/pwm-ipq.c | 275 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 288 insertions(+)
 create mode 100644 drivers/pwm/pwm-ipq.c

Comments

Uwe Kleine-König Jan. 19, 2022, 5:24 p.m. UTC | #1
On Tue, Dec 14, 2021 at 06:27:17PM +0200, Baruch Siach wrote:
> From: Baruch Siach <baruch.siach@siklu.com>
> 
> Driver for the PWM block in Qualcomm IPQ6018 line of SoCs. Based on
> driver from downstream Codeaurora kernel tree. Removed support for older
> (V1) variants because I have no access to that hardware.
> 
> Tested on IPQ6010 based hardware.
> 
> Signed-off-by: Baruch Siach <baruch.siach@siklu.com>
> ---
> v10:
> 
>   Restore round up in pwm_div calculation; otherwise diff is always <=
>   0, so only bingo match works
> 
>   Don't overwrite min_diff on every loop iteration
> 
> v9:
> 
> Address comment from Uwe Kleine-König:
> 
>   Use period_ns*rate in dividers calculation for better accuracy
> 
>   Round down pre_div and pwm_div
> 
>   Add a comment explaining why pwm_div can't underflow
> 
>   Add a comment explaining why pre_div > pwm_div end the search loop
> 
>   Drop 'CFG_' from register macros
> 
>   Rename to_ipq_pwm_chip() to ipq_pwm_from_chip()
> 
>   Change bare 'unsigned' to 'unsigned int'
> 
>   Clarify the comment on separate REG1 write for enable/disable
> 
>   Round up the period value in .get_state
> 
>   Use direct readl/writel so no need to check for regmap errors
> 
> v7:
> 
>   Change 'offset' to 'reg' for the tcsr offset (Rob)
> 
>   Drop clock name; there is only one clock (Bjorn)
> 
>   Simplify probe failure code path (Bjorn)
> 
> v6:
> 
> Address Uwe Kleine-König review comments:
> 
>   Drop IPQ_PWM_MAX_DEVICES
> 
>   Rely on assigned-clock-rates; drop IPQ_PWM_CLK_SRC_FREQ
> 
>   Simplify register offset calculation
> 
>   Calculate duty cycle more precisely
> 
>   Refuse to set inverted polarity
> 
>   Drop redundant IPQ_PWM_REG1_ENABLE bit clear
> 
>   Remove x1000 factor in pwm_div calculation, use rate directly, and round up
> 
>   Choose initial pre_div such that pwm_div < IPQ_PWM_MAX_DIV
> 
>   Ensure pre_div <= pwm_div
> 
>   Rename close_ to best_
> 
>   Explain in comment why effective_div doesn't overflow
> 
>   Limit pwm_div to IPQ_PWM_MAX_DIV - 1 to allow 100% duty cycle
> 
>   Disable clock only after pwmchip_remove()
> 
>   const pwm_ops
> 
> Other changes:
> 
>   Add missing linux/bitfield.h header include (kernel test robot)
> 
>   Adjust code for PWM device node under TCSR (Rob Herring)
> 
> v5:
> 
> Use &tcsr_q6 syscon to access registers (Bjorn Andersson)
> 
> Address Uwe Kleine-König review comments:
> 
>   Implement .get_state()
> 
>   Add IPQ_PWM_ prefix to local macros
> 
>   Use GENMASK/BIT/FIELD_PREP for register fields access
> 
>   Make type of config_div_and_duty() parameters consistent
> 
>   Derive IPQ_PWM_MIN_PERIOD_NS from IPQ_PWM_CLK_SRC_FREQ
> 
>   Integrate enable/disable into config_div_and_duty() to save register read,
>   and reduce frequency glitch on update
> 
>   Use min() instead of min_t()
> 
>   Fix comment format
> 
>   Use dev_err_probe() to indicate probe step failure
> 
>   Add missing clk_disable_unprepare() in .remove
> 
>   Don't set .owner
> 
> v4:
> 
>   Use div64_u64() to fix link for 32-bit targets ((kernel test robot
>   <lkp@intel.com>, Uwe Kleine-König)
> 
> v3:
> 
>   s/qcom,pwm-ipq6018/qcom,ipq6018-pwm/ (Rob Herring)
> 
>   Fix integer overflow on 32-bit targets (kernel test robot <lkp@intel.com>)
> 
> v2:
> 
> Address Uwe Kleine-König review comments:
> 
>   Fix period calculation when out of range
> 
>   Don't set period larger than requested
> 
>   Remove PWM disable on configuration change
> 
>   Implement .apply instead of non-atomic .config/.enable/.disable
> 
>   Don't modify PWM on .request/.free
> 
>   Check pwm_div underflow
> 
>   Fix various code and comment formatting issues
> 
> Other changes:
> 
>   Use u64 divisor safe division
> 
>   Remove now empty .request/.free
> ---
>  drivers/pwm/Kconfig   |  12 ++
>  drivers/pwm/Makefile  |   1 +
>  drivers/pwm/pwm-ipq.c | 275 ++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 288 insertions(+)
>  create mode 100644 drivers/pwm/pwm-ipq.c
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 21e3b05a5153..e39718137ecd 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -260,6 +260,18 @@ config PWM_INTEL_LGM
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-intel-lgm.
>  
> +config PWM_IPQ
> +	tristate "IPQ PWM support"
> +	depends on ARCH_QCOM || COMPILE_TEST
> +	depends on HAVE_CLK && HAS_IOMEM
> +	help
> +	  Generic PWM framework driver for IPQ PWM block which supports
> +	  4 pwm channels. Each of the these channels can be configured
> +	  independent of each other.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called pwm-ipq.
> +
>  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 708840b7fba8..7402feae4b36 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -22,6 +22,7 @@ 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-$(CONFIG_PWM_IPQ)		+= pwm-ipq.o
>  obj-$(CONFIG_PWM_IQS620A)	+= pwm-iqs620a.o
>  obj-$(CONFIG_PWM_JZ4740)	+= pwm-jz4740.o
>  obj-$(CONFIG_PWM_KEEMBAY)	+= pwm-keembay.o
> diff --git a/drivers/pwm/pwm-ipq.c b/drivers/pwm/pwm-ipq.c
> new file mode 100644
> index 000000000000..3764010808f0
> --- /dev/null
> +++ b/drivers/pwm/pwm-ipq.c
> @@ -0,0 +1,275 @@
> +// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
> +/*
> + * Copyright (c) 2016-2017, 2020 The Linux Foundation. All rights reserved.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +#include <linux/clk.h>
> +#include <linux/io.h>
> +#include <linux/of.h>
> +#include <linux/math64.h>
> +#include <linux/of_device.h>
> +#include <linux/bitfield.h>
> +
> +/* The frequency range supported is 1 Hz to clock rate */
> +#define IPQ_PWM_MAX_PERIOD_NS	((u64)NSEC_PER_SEC)
> +
> +/*
> + * The max value specified for each field is based on the number of bits
> + * in the pwm control register for that field
> + */
> +#define IPQ_PWM_MAX_DIV		0xFFFF
> +
> +/*
> + * Two 32-bit registers for each PWM: REG0, and REG1.
> + * Base offset for PWM #i is at 8 * #i.
> + */
> +#define IPQ_PWM_REG0			0 /*PWM_DIV PWM_HI*/
> +#define IPQ_PWM_REG0_PWM_DIV		GENMASK(15, 0)
> +#define IPQ_PWM_REG0_HI_DURATION	GENMASK(31, 16)

PWM_HI in the comment of IPQ_PWM_REG0 vs. HI_DURATION? Should this
match? I'd say the comment is redundant.

> +#define IPQ_PWM_REG1			4 /*ENABLE UPDATE PWM_PRE_DIV*/
> +#define IPQ_PWM_REG1_PRE_DIV		GENMASK(15, 0)
> +/*
> + * Enable bit is set to enable output toggling in pwm device.
> + * Update bit is set to reflect the changed divider and high duration
> + * values in register.
> + */
> +#define IPQ_PWM_REG1_UPDATE		BIT(30)
> +#define IPQ_PWM_REG1_ENABLE		BIT(31)
> +
> +
> +struct ipq_pwm_chip {
> +	struct pwm_chip chip;
> +	struct clk *clk;
> +	void __iomem *mem;
> +};
> +
> +static struct ipq_pwm_chip *ipq_pwm_from_chip(struct pwm_chip *chip)
> +{
> +	return container_of(chip, struct ipq_pwm_chip, chip);
> +}
> +
> +static unsigned int ipq_pwm_reg_read(struct pwm_device *pwm, unsigned int reg)
> +{
> +	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(pwm->chip);
> +	unsigned int off = 8 * pwm->hwpwm + reg;
> +
> +	return readl(ipq_chip->mem + off);
> +}
> +
> +static void ipq_pwm_reg_write(struct pwm_device *pwm, unsigned int reg,
> +			      unsigned int val)
> +{
> +	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(pwm->chip);
> +	unsigned int off = 8 * pwm->hwpwm + reg;
> +
> +	writel(val, ipq_chip->mem + off);
> +}
> +
> +static void config_div_and_duty(struct pwm_device *pwm, unsigned int pre_div,
> +			unsigned int pwm_div, unsigned long rate, u64 duty_ns,
> +			bool enable)
> +{
> +	unsigned long hi_dur;
> +	unsigned long val = 0;
> +
> +	/*
> +	 * high duration = pwm duty * (pwm div + 1)
> +	 * pwm duty = duty_ns / period_ns
> +	 */
> +	hi_dur = div64_u64(duty_ns * rate, (pre_div + 1) * NSEC_PER_SEC);
> +
> +	val = FIELD_PREP(IPQ_PWM_REG0_HI_DURATION, hi_dur) |
> +		FIELD_PREP(IPQ_PWM_REG0_PWM_DIV, pwm_div);
> +	ipq_pwm_reg_write(pwm, IPQ_PWM_REG0, val);
> +
> +	val = FIELD_PREP(IPQ_PWM_REG1_PRE_DIV, pre_div);
> +	ipq_pwm_reg_write(pwm, IPQ_PWM_REG1, val);
> +
> +	/* PWM enable toggle needs a separate write to REG1 */
> +	val |= IPQ_PWM_REG1_UPDATE;
> +	if (enable)
> +		val |= IPQ_PWM_REG1_ENABLE;
> +	ipq_pwm_reg_write(pwm, IPQ_PWM_REG1, val);
> +}
> +
> +static int ipq_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +			 const struct pwm_state *state)
> +{
> +	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(chip);
> +	unsigned int pre_div, pwm_div, best_pre_div, best_pwm_div;
> +	unsigned long rate = clk_get_rate(ipq_chip->clk);
> +	u64 period_ns, duty_ns, period_rate;
> +	u64 min_diff;
> +
> +	if (state->polarity != PWM_POLARITY_NORMAL)
> +		return -EINVAL;
> +
> +	if (state->period < div64_u64(NSEC_PER_SEC, rate))
> +		return -ERANGE;

NSEC_PER_SEC / rate is the smallest period you can achieve, right?
Consider rate = 33333 (Hz), then the minimal period is
30000.30000300003 ns. So you should refuse a request to configure
state->period = 30000, but as div64_u64(1000000000, 33333) is 30000 you
don't.

> +	period_ns = min(state->period, IPQ_PWM_MAX_PERIOD_NS);
> +	duty_ns = min(state->duty_cycle, period_ns);
> +
> +	/*
> +	 * period_ns is 1G or less. As long as rate is less than 16 GHz this
> +	 * does not overflow.

Well, rate cannot be bigger than 4294967295 because an unsigned long
cannot hold a bigger value.

> +	 */
> +	period_rate = period_ns * rate;
> +	best_pre_div = IPQ_PWM_MAX_DIV;
> +	best_pwm_div = IPQ_PWM_MAX_DIV;
> +	/* Initial pre_div value such that pwm_div < IPQ_PWM_MAX_DIV */
> +	pre_div = div64_u64(period_rate,
> +			(u64)NSEC_PER_SEC * (IPQ_PWM_MAX_DIV + 1));

Hmmm, we want 

	(pre_div + 1) * (pwm_div + 1) * NSEC_PER_SEC
	-------------------------------------------- <= period_ns
	                  rate

, right? Resolving that for pre_div this gives:

	                period_ns * rate
	pre_div <= ----------------------------
	           NSEC_PER_SEC * (pwm_div + 1)

The term on the right hand side is maximal for pwm_div == 0 so the
possible values for pre_div are

	0 ... min(div64_u64(period_rate / NSEC_PER_SEC), IPQ_PWM_MAX_DIV)

isn't it? If so, your algorithm is wrong as you're iterating over

	div64_u64(period_rate, NSEC_PER_SEC * (IPQ_PWM_MAX_DIV + 1)) ... IPQ_PWM_MAX_DIV

> +	min_diff = period_rate;
> +
> +	for (; pre_div <= IPQ_PWM_MAX_DIV; pre_div++) {
> +		long long diff;
> +
> +		pwm_div = DIV64_U64_ROUND_UP(period_rate,
> +				(u64)NSEC_PER_SEC * (pre_div + 1));
> +		/* pwm_div is unsigned; the check below catches underflow */
> +		pwm_div--;

What underflow? DIV64_U64_ROUND_UP returns > 0 assuming period_rate > 0.
So pwm_div - 1 doesn't underflow?!

The task here is to calculate the biggest pwm_div for a given pre_div
such that


	(pre_div + 1) * (pwm_div + 1) * NSEC_PER_SEC
	-------------------------------------------- <= period_ns
	                   rate

right?

This is equivalent to:

	                  period_ns * rate
	pre_div <= ---------------------------- - 1
	           (pre_div + 1) * NSEC_PER_SEC

As pre_div is integer, rounding down should be fine?!

> +		/*
> +		 * pre_div and pwm_div values swap produces the same
> +		 * result. This loop goes over all pre_div <= pwm_div
> +		 * combinations. The rest are equivalent.
> +		 */

I'd write:

	/*
	 * Swapping values for pre_div and pwm_div produces the same
	 * period length. So we can skip all settings with pre_div <
	 * pwm_div which results in bigger constraints for selecting the
	 * duty_cycle than with the two values swapped.
	 */

> +		if (pre_div > pwm_div)
> +			break;
> +
> +		/*
> +		 * Make sure we can do 100% duty cycle where
> +		 * hi_dur == pwm_div + 1
> +		 */
> +		if (pwm_div > IPQ_PWM_MAX_DIV - 1)
> +			continue;
> +
> +		diff = ((uint64_t)NSEC_PER_SEC * (pre_div + 1) * (pwm_div + 1))
> +			- period_rate;
> +
> +		if (diff < 0) /* period larger than requested */
> +			continue;

This shouldn't happen if the above calculation is correct.

> +		if (diff == 0) { /* bingo */
> +			best_pre_div = pre_div;
> +			best_pwm_div = pwm_div;
> +			break;
> +		}
> +		if (diff < min_diff) {
> +			min_diff = diff;
> +			best_pre_div = pre_div;
> +			best_pwm_div = pwm_div;
> +		}

This can be simplified as:

		if (diff < min_diff) {
			best_pre_div = pre_div;
			best_pwm_div = pwm_div;
			min_diff = diff;

			if (min_diff == 0)
				/* bingo! */
				break;
		}

> +	}
> +
> +	/* config divider values for the closest possible frequency */
> +	config_div_and_duty(pwm, best_pre_div, best_pwm_div,
> +			    rate, duty_ns, state->enabled);
> +
> +	return 0;
> +}
> +
> +static void ipq_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> +			      struct pwm_state *state)
> +{
> +	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(chip);
> +	unsigned long rate = clk_get_rate(ipq_chip->clk);
> +	unsigned int pre_div, pwm_div, hi_dur;
> +	u64 effective_div, hi_div;
> +	u32 reg0, reg1;
> +
> +	reg0 = ipq_pwm_reg_read(pwm, IPQ_PWM_REG0);
> +	reg1 = ipq_pwm_reg_read(pwm, IPQ_PWM_REG1);
> +
> +	state->polarity = PWM_POLARITY_NORMAL;
> +	state->enabled = reg1 & IPQ_PWM_REG1_ENABLE;
> +
> +	pwm_div = FIELD_GET(IPQ_PWM_REG0_PWM_DIV, reg0);
> +	hi_dur = FIELD_GET(IPQ_PWM_REG0_HI_DURATION, reg0);
> +	pre_div = FIELD_GET(IPQ_PWM_REG1_PRE_DIV, reg1);
> +
> +	/* No overflow here, both pre_div and pwm_div <= 0xffff */
> +	effective_div = (u64)(pre_div + 1) * (pwm_div + 1);
> +	state->period = DIV64_U64_ROUND_UP(effective_div * NSEC_PER_SEC, rate);
> +
> +	hi_div = hi_dur * (pre_div + 1);
> +	state->duty_cycle = div64_u64(hi_div * NSEC_PER_SEC, rate);

This must be round up for the same reasons as for period.

> +}

Best regards
Uwe
Baruch Siach Jan. 25, 2022, 1:03 p.m. UTC | #2
Hi Uwe,

Thanks for your detailed review and comments. Please find my comments
below.

On Wed, Jan 19 2022, Uwe Kleine-König wrote:
> On Tue, Dec 14, 2021 at 06:27:17PM +0200, Baruch Siach wrote:
>> From: Baruch Siach <baruch.siach@siklu.com>
>> 
>> Driver for the PWM block in Qualcomm IPQ6018 line of SoCs. Based on
>> driver from downstream Codeaurora kernel tree. Removed support for older
>> (V1) variants because I have no access to that hardware.
>> 
>> Tested on IPQ6010 based hardware.
>> 
>> Signed-off-by: Baruch Siach <baruch.siach@siklu.com>
>> ---
>> v10:
>> 
>>   Restore round up in pwm_div calculation; otherwise diff is always <=
>>   0, so only bingo match works
>> 
>>   Don't overwrite min_diff on every loop iteration
>> 
>> v9:
>> 
>> Address comment from Uwe Kleine-König:
>> 
>>   Use period_ns*rate in dividers calculation for better accuracy
>> 
>>   Round down pre_div and pwm_div
>> 
>>   Add a comment explaining why pwm_div can't underflow
>> 
>>   Add a comment explaining why pre_div > pwm_div end the search loop
>> 
>>   Drop 'CFG_' from register macros
>> 
>>   Rename to_ipq_pwm_chip() to ipq_pwm_from_chip()
>> 
>>   Change bare 'unsigned' to 'unsigned int'
>> 
>>   Clarify the comment on separate REG1 write for enable/disable
>> 
>>   Round up the period value in .get_state
>> 
>>   Use direct readl/writel so no need to check for regmap errors
>> 
>> v7:
>> 
>>   Change 'offset' to 'reg' for the tcsr offset (Rob)
>> 
>>   Drop clock name; there is only one clock (Bjorn)
>> 
>>   Simplify probe failure code path (Bjorn)
>> 
>> v6:
>> 
>> Address Uwe Kleine-König review comments:
>> 
>>   Drop IPQ_PWM_MAX_DEVICES
>> 
>>   Rely on assigned-clock-rates; drop IPQ_PWM_CLK_SRC_FREQ
>> 
>>   Simplify register offset calculation
>> 
>>   Calculate duty cycle more precisely
>> 
>>   Refuse to set inverted polarity
>> 
>>   Drop redundant IPQ_PWM_REG1_ENABLE bit clear
>> 
>>   Remove x1000 factor in pwm_div calculation, use rate directly, and round up
>> 
>>   Choose initial pre_div such that pwm_div < IPQ_PWM_MAX_DIV
>> 
>>   Ensure pre_div <= pwm_div
>> 
>>   Rename close_ to best_
>> 
>>   Explain in comment why effective_div doesn't overflow
>> 
>>   Limit pwm_div to IPQ_PWM_MAX_DIV - 1 to allow 100% duty cycle
>> 
>>   Disable clock only after pwmchip_remove()
>> 
>>   const pwm_ops
>> 
>> Other changes:
>> 
>>   Add missing linux/bitfield.h header include (kernel test robot)
>> 
>>   Adjust code for PWM device node under TCSR (Rob Herring)
>> 
>> v5:
>> 
>> Use &tcsr_q6 syscon to access registers (Bjorn Andersson)
>> 
>> Address Uwe Kleine-König review comments:
>> 
>>   Implement .get_state()
>> 
>>   Add IPQ_PWM_ prefix to local macros
>> 
>>   Use GENMASK/BIT/FIELD_PREP for register fields access
>> 
>>   Make type of config_div_and_duty() parameters consistent
>> 
>>   Derive IPQ_PWM_MIN_PERIOD_NS from IPQ_PWM_CLK_SRC_FREQ
>> 
>>   Integrate enable/disable into config_div_and_duty() to save register read,
>>   and reduce frequency glitch on update
>> 
>>   Use min() instead of min_t()
>> 
>>   Fix comment format
>> 
>>   Use dev_err_probe() to indicate probe step failure
>> 
>>   Add missing clk_disable_unprepare() in .remove
>> 
>>   Don't set .owner
>> 
>> v4:
>> 
>>   Use div64_u64() to fix link for 32-bit targets ((kernel test robot
>>   <lkp@intel.com>, Uwe Kleine-König)
>> 
>> v3:
>> 
>>   s/qcom,pwm-ipq6018/qcom,ipq6018-pwm/ (Rob Herring)
>> 
>>   Fix integer overflow on 32-bit targets (kernel test robot <lkp@intel.com>)
>> 
>> v2:
>> 
>> Address Uwe Kleine-König review comments:
>> 
>>   Fix period calculation when out of range
>> 
>>   Don't set period larger than requested
>> 
>>   Remove PWM disable on configuration change
>> 
>>   Implement .apply instead of non-atomic .config/.enable/.disable
>> 
>>   Don't modify PWM on .request/.free
>> 
>>   Check pwm_div underflow
>> 
>>   Fix various code and comment formatting issues
>> 
>> Other changes:
>> 
>>   Use u64 divisor safe division
>> 
>>   Remove now empty .request/.free
>> ---
>>  drivers/pwm/Kconfig   |  12 ++
>>  drivers/pwm/Makefile  |   1 +
>>  drivers/pwm/pwm-ipq.c | 275 ++++++++++++++++++++++++++++++++++++++++++
>>  3 files changed, 288 insertions(+)
>>  create mode 100644 drivers/pwm/pwm-ipq.c
>> 
>> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
>> index 21e3b05a5153..e39718137ecd 100644
>> --- a/drivers/pwm/Kconfig
>> +++ b/drivers/pwm/Kconfig
>> @@ -260,6 +260,18 @@ config PWM_INTEL_LGM
>>  	  To compile this driver as a module, choose M here: the module
>>  	  will be called pwm-intel-lgm.
>>  
>> +config PWM_IPQ
>> +	tristate "IPQ PWM support"
>> +	depends on ARCH_QCOM || COMPILE_TEST
>> +	depends on HAVE_CLK && HAS_IOMEM
>> +	help
>> +	  Generic PWM framework driver for IPQ PWM block which supports
>> +	  4 pwm channels. Each of the these channels can be configured
>> +	  independent of each other.
>> +
>> +	  To compile this driver as a module, choose M here: the module
>> +	  will be called pwm-ipq.
>> +
>>  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 708840b7fba8..7402feae4b36 100644
>> --- a/drivers/pwm/Makefile
>> +++ b/drivers/pwm/Makefile
>> @@ -22,6 +22,7 @@ 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-$(CONFIG_PWM_IPQ)		+= pwm-ipq.o
>>  obj-$(CONFIG_PWM_IQS620A)	+= pwm-iqs620a.o
>>  obj-$(CONFIG_PWM_JZ4740)	+= pwm-jz4740.o
>>  obj-$(CONFIG_PWM_KEEMBAY)	+= pwm-keembay.o
>> diff --git a/drivers/pwm/pwm-ipq.c b/drivers/pwm/pwm-ipq.c
>> new file mode 100644
>> index 000000000000..3764010808f0
>> --- /dev/null
>> +++ b/drivers/pwm/pwm-ipq.c
>> @@ -0,0 +1,275 @@
>> +// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
>> +/*
>> + * Copyright (c) 2016-2017, 2020 The Linux Foundation. All rights reserved.
>> + */
>> +
>> +#include <linux/module.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/pwm.h>
>> +#include <linux/clk.h>
>> +#include <linux/io.h>
>> +#include <linux/of.h>
>> +#include <linux/math64.h>
>> +#include <linux/of_device.h>
>> +#include <linux/bitfield.h>
>> +
>> +/* The frequency range supported is 1 Hz to clock rate */
>> +#define IPQ_PWM_MAX_PERIOD_NS	((u64)NSEC_PER_SEC)
>> +
>> +/*
>> + * The max value specified for each field is based on the number of bits
>> + * in the pwm control register for that field
>> + */
>> +#define IPQ_PWM_MAX_DIV		0xFFFF
>> +
>> +/*
>> + * Two 32-bit registers for each PWM: REG0, and REG1.
>> + * Base offset for PWM #i is at 8 * #i.
>> + */
>> +#define IPQ_PWM_REG0			0 /*PWM_DIV PWM_HI*/
>> +#define IPQ_PWM_REG0_PWM_DIV		GENMASK(15, 0)
>> +#define IPQ_PWM_REG0_HI_DURATION	GENMASK(31, 16)
>
> PWM_HI in the comment of IPQ_PWM_REG0 vs. HI_DURATION? Should this
> match? I'd say the comment is redundant.
>
>> +#define IPQ_PWM_REG1			4 /*ENABLE UPDATE PWM_PRE_DIV*/
>> +#define IPQ_PWM_REG1_PRE_DIV		GENMASK(15, 0)
>> +/*
>> + * Enable bit is set to enable output toggling in pwm device.
>> + * Update bit is set to reflect the changed divider and high duration
>> + * values in register.
>> + */
>> +#define IPQ_PWM_REG1_UPDATE		BIT(30)
>> +#define IPQ_PWM_REG1_ENABLE		BIT(31)
>> +
>> +
>> +struct ipq_pwm_chip {
>> +	struct pwm_chip chip;
>> +	struct clk *clk;
>> +	void __iomem *mem;
>> +};
>> +
>> +static struct ipq_pwm_chip *ipq_pwm_from_chip(struct pwm_chip *chip)
>> +{
>> +	return container_of(chip, struct ipq_pwm_chip, chip);
>> +}
>> +
>> +static unsigned int ipq_pwm_reg_read(struct pwm_device *pwm, unsigned int reg)
>> +{
>> +	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(pwm->chip);
>> +	unsigned int off = 8 * pwm->hwpwm + reg;
>> +
>> +	return readl(ipq_chip->mem + off);
>> +}
>> +
>> +static void ipq_pwm_reg_write(struct pwm_device *pwm, unsigned int reg,
>> +			      unsigned int val)
>> +{
>> +	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(pwm->chip);
>> +	unsigned int off = 8 * pwm->hwpwm + reg;
>> +
>> +	writel(val, ipq_chip->mem + off);
>> +}
>> +
>> +static void config_div_and_duty(struct pwm_device *pwm, unsigned int pre_div,
>> +			unsigned int pwm_div, unsigned long rate, u64 duty_ns,
>> +			bool enable)
>> +{
>> +	unsigned long hi_dur;
>> +	unsigned long val = 0;
>> +
>> +	/*
>> +	 * high duration = pwm duty * (pwm div + 1)
>> +	 * pwm duty = duty_ns / period_ns
>> +	 */
>> +	hi_dur = div64_u64(duty_ns * rate, (pre_div + 1) * NSEC_PER_SEC);
>> +
>> +	val = FIELD_PREP(IPQ_PWM_REG0_HI_DURATION, hi_dur) |
>> +		FIELD_PREP(IPQ_PWM_REG0_PWM_DIV, pwm_div);
>> +	ipq_pwm_reg_write(pwm, IPQ_PWM_REG0, val);
>> +
>> +	val = FIELD_PREP(IPQ_PWM_REG1_PRE_DIV, pre_div);
>> +	ipq_pwm_reg_write(pwm, IPQ_PWM_REG1, val);
>> +
>> +	/* PWM enable toggle needs a separate write to REG1 */
>> +	val |= IPQ_PWM_REG1_UPDATE;
>> +	if (enable)
>> +		val |= IPQ_PWM_REG1_ENABLE;
>> +	ipq_pwm_reg_write(pwm, IPQ_PWM_REG1, val);
>> +}
>> +
>> +static int ipq_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>> +			 const struct pwm_state *state)
>> +{
>> +	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(chip);
>> +	unsigned int pre_div, pwm_div, best_pre_div, best_pwm_div;
>> +	unsigned long rate = clk_get_rate(ipq_chip->clk);
>> +	u64 period_ns, duty_ns, period_rate;
>> +	u64 min_diff;
>> +
>> +	if (state->polarity != PWM_POLARITY_NORMAL)
>> +		return -EINVAL;
>> +
>> +	if (state->period < div64_u64(NSEC_PER_SEC, rate))
>> +		return -ERANGE;
>
> NSEC_PER_SEC / rate is the smallest period you can achieve, right?
> Consider rate = 33333 (Hz), then the minimal period is
> 30000.30000300003 ns. So you should refuse a request to configure
> state->period = 30000, but as div64_u64(1000000000, 33333) is 30000 you
> don't.
>
>> +	period_ns = min(state->period, IPQ_PWM_MAX_PERIOD_NS);
>> +	duty_ns = min(state->duty_cycle, period_ns);
>> +
>> +	/*
>> +	 * period_ns is 1G or less. As long as rate is less than 16 GHz this
>> +	 * does not overflow.
>
> Well, rate cannot be bigger than 4294967295 because an unsigned long
> cannot hold a bigger value.

On 64-bit systems __SIZEOF_LONG__ is 8, which can hold more than 2^32.

>> +	 */
>> +	period_rate = period_ns * rate;
>> +	best_pre_div = IPQ_PWM_MAX_DIV;
>> +	best_pwm_div = IPQ_PWM_MAX_DIV;
>> +	/* Initial pre_div value such that pwm_div < IPQ_PWM_MAX_DIV */

Note this comment.

>> +	pre_div = div64_u64(period_rate,
>> +			(u64)NSEC_PER_SEC * (IPQ_PWM_MAX_DIV + 1));
>
> Hmmm, we want 
>
> 	(pre_div + 1) * (pwm_div + 1) * NSEC_PER_SEC
> 	-------------------------------------------- <= period_ns
> 	                  rate
>
> , right? Resolving that for pre_div this gives:
>
> 	                period_ns * rate
> 	pre_div <= ----------------------------
> 	           NSEC_PER_SEC * (pwm_div + 1)
>
> The term on the right hand side is maximal for pwm_div == 0 so the
> possible values for pre_div are
>
> 	0 ... min(div64_u64(period_rate / NSEC_PER_SEC), IPQ_PWM_MAX_DIV)
>
> isn't it?

I don't think so. pre_div == 0 will produce pwm_div larger than
IPQ_PWM_MAX_DIV for a large period_rate value. The initial pre_div here is the
smallest value that produces pwm_div within it limit.

> If so, your algorithm is wrong as you're iterating over
>
> 	div64_u64(period_rate, NSEC_PER_SEC * (IPQ_PWM_MAX_DIV + 1)) ... IPQ_PWM_MAX_DIV

The loop stops when pre_div > pwm_div. That should be before pre_div ==
IPQ_PWM_MAX_DIV because pwm_div <= IPQ_PWM_MAX_DIV. Should I put the pre_div >
pwm_div condition directly in the for statement?

>> +	min_diff = period_rate;
>> +
>> +	for (; pre_div <= IPQ_PWM_MAX_DIV; pre_div++) {
>> +		long long diff;
>> +
>> +		pwm_div = DIV64_U64_ROUND_UP(period_rate,
>> +				(u64)NSEC_PER_SEC * (pre_div + 1));
>> +		/* pwm_div is unsigned; the check below catches underflow */
>> +		pwm_div--;
>
> What underflow? DIV64_U64_ROUND_UP returns > 0 assuming period_rate > 0.
> So pwm_div - 1 doesn't underflow?!

I'll update the comment.

> The task here is to calculate the biggest pwm_div for a given pre_div
> such that
>
>
> 	(pre_div + 1) * (pwm_div + 1) * NSEC_PER_SEC
> 	-------------------------------------------- <= period_ns
> 	                   rate
>
> right?
>
> This is equivalent to:
>
> 	                  period_ns * rate
> 	pre_div <= ---------------------------- - 1
> 	           (pre_div + 1) * NSEC_PER_SEC
>
> As pre_div is integer, rounding down should be fine?!

I can't follow. With round down (as in v8) the result is always:

  NSEC_PER_SEC * (pre_div + 1) * (pwm_div + 1) <= period_rate

As a result, 'diff' calculation below will always produce diff <= 0. When
there is no diff == 0 result (bingo) we get IPQ_PWM_MAX_DIV in both best_
values at the end of the loop.

Do we actually need diff > 0 in the condition below?

>> +		/*
>> +		 * pre_div and pwm_div values swap produces the same
>> +		 * result. This loop goes over all pre_div <= pwm_div
>> +		 * combinations. The rest are equivalent.
>> +		 */
>
> I'd write:
>
> 	/*
> 	 * Swapping values for pre_div and pwm_div produces the same
> 	 * period length. So we can skip all settings with pre_div <
> 	 * pwm_div which results in bigger constraints for selecting the
> 	 * duty_cycle than with the two values swapped.
> 	 */

I'll take your wording with inverted inequality sign.

Thanks,
baruch

>> +		if (pre_div > pwm_div)
>> +			break;
>> +
>> +		/*
>> +		 * Make sure we can do 100% duty cycle where
>> +		 * hi_dur == pwm_div + 1
>> +		 */
>> +		if (pwm_div > IPQ_PWM_MAX_DIV - 1)
>> +			continue;
>> +
>> +		diff = ((uint64_t)NSEC_PER_SEC * (pre_div + 1) * (pwm_div + 1))
>> +			- period_rate;
>> +
>> +		if (diff < 0) /* period larger than requested */
>> +			continue;
>
> This shouldn't happen if the above calculation is correct.
>
>> +		if (diff == 0) { /* bingo */
>> +			best_pre_div = pre_div;
>> +			best_pwm_div = pwm_div;
>> +			break;
>> +		}
>> +		if (diff < min_diff) {
>> +			min_diff = diff;
>> +			best_pre_div = pre_div;
>> +			best_pwm_div = pwm_div;
>> +		}
>
> This can be simplified as:
>
> 		if (diff < min_diff) {
> 			best_pre_div = pre_div;
> 			best_pwm_div = pwm_div;
> 			min_diff = diff;
>
> 			if (min_diff == 0)
> 				/* bingo! */
> 				break;
> 		}
>
>> +	}
>> +
>> +	/* config divider values for the closest possible frequency */
>> +	config_div_and_duty(pwm, best_pre_div, best_pwm_div,
>> +			    rate, duty_ns, state->enabled);
>> +
>> +	return 0;
>> +}
>> +
>> +static void ipq_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
>> +			      struct pwm_state *state)
>> +{
>> +	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(chip);
>> +	unsigned long rate = clk_get_rate(ipq_chip->clk);
>> +	unsigned int pre_div, pwm_div, hi_dur;
>> +	u64 effective_div, hi_div;
>> +	u32 reg0, reg1;
>> +
>> +	reg0 = ipq_pwm_reg_read(pwm, IPQ_PWM_REG0);
>> +	reg1 = ipq_pwm_reg_read(pwm, IPQ_PWM_REG1);
>> +
>> +	state->polarity = PWM_POLARITY_NORMAL;
>> +	state->enabled = reg1 & IPQ_PWM_REG1_ENABLE;
>> +
>> +	pwm_div = FIELD_GET(IPQ_PWM_REG0_PWM_DIV, reg0);
>> +	hi_dur = FIELD_GET(IPQ_PWM_REG0_HI_DURATION, reg0);
>> +	pre_div = FIELD_GET(IPQ_PWM_REG1_PRE_DIV, reg1);
>> +
>> +	/* No overflow here, both pre_div and pwm_div <= 0xffff */
>> +	effective_div = (u64)(pre_div + 1) * (pwm_div + 1);
>> +	state->period = DIV64_U64_ROUND_UP(effective_div * NSEC_PER_SEC, rate);
>> +
>> +	hi_div = hi_dur * (pre_div + 1);
>> +	state->duty_cycle = div64_u64(hi_div * NSEC_PER_SEC, rate);
>
> This must be round up for the same reasons as for period.
>
>> +}
>
> Best regards
> Uwe
Uwe Kleine-König Jan. 25, 2022, 4:12 p.m. UTC | #3
Hello Baruch,

On Tue, Jan 25, 2022 at 03:03:08PM +0200, Baruch Siach wrote:
> On Wed, Jan 19 2022, Uwe Kleine-König wrote:
> > On Tue, Dec 14, 2021 at 06:27:17PM +0200, Baruch Siach wrote:
> >> From: Baruch Siach <baruch.siach@siklu.com>
> >> 
> >> Driver for the PWM block in Qualcomm IPQ6018 line of SoCs. Based on
> >> driver from downstream Codeaurora kernel tree. Removed support for older
> >> (V1) variants because I have no access to that hardware.
> >> 
> >> Tested on IPQ6010 based hardware.
> >> 
> >> Signed-off-by: Baruch Siach <baruch.siach@siklu.com>
> >> ---
> >> v10:
> >> 
> >>   Restore round up in pwm_div calculation; otherwise diff is always <=
> >>   0, so only bingo match works
> >> 
> >>   Don't overwrite min_diff on every loop iteration
> >> 
> >> v9:
> >> 
> >> Address comment from Uwe Kleine-König:
> >> 
> >>   Use period_ns*rate in dividers calculation for better accuracy
> >> 
> >>   Round down pre_div and pwm_div
> >> 
> >>   Add a comment explaining why pwm_div can't underflow
> >> 
> >>   Add a comment explaining why pre_div > pwm_div end the search loop
> >> 
> >>   Drop 'CFG_' from register macros
> >> 
> >>   Rename to_ipq_pwm_chip() to ipq_pwm_from_chip()
> >> 
> >>   Change bare 'unsigned' to 'unsigned int'
> >> 
> >>   Clarify the comment on separate REG1 write for enable/disable
> >> 
> >>   Round up the period value in .get_state
> >> 
> >>   Use direct readl/writel so no need to check for regmap errors
> >> 
> >> v7:
> >> 
> >>   Change 'offset' to 'reg' for the tcsr offset (Rob)
> >> 
> >>   Drop clock name; there is only one clock (Bjorn)
> >> 
> >>   Simplify probe failure code path (Bjorn)
> >> 
> >> v6:
> >> 
> >> Address Uwe Kleine-König review comments:
> >> 
> >>   Drop IPQ_PWM_MAX_DEVICES
> >> 
> >>   Rely on assigned-clock-rates; drop IPQ_PWM_CLK_SRC_FREQ
> >> 
> >>   Simplify register offset calculation
> >> 
> >>   Calculate duty cycle more precisely
> >> 
> >>   Refuse to set inverted polarity
> >> 
> >>   Drop redundant IPQ_PWM_REG1_ENABLE bit clear
> >> 
> >>   Remove x1000 factor in pwm_div calculation, use rate directly, and round up
> >> 
> >>   Choose initial pre_div such that pwm_div < IPQ_PWM_MAX_DIV
> >> 
> >>   Ensure pre_div <= pwm_div
> >> 
> >>   Rename close_ to best_
> >> 
> >>   Explain in comment why effective_div doesn't overflow
> >> 
> >>   Limit pwm_div to IPQ_PWM_MAX_DIV - 1 to allow 100% duty cycle
> >> 
> >>   Disable clock only after pwmchip_remove()
> >> 
> >>   const pwm_ops
> >> 
> >> Other changes:
> >> 
> >>   Add missing linux/bitfield.h header include (kernel test robot)
> >> 
> >>   Adjust code for PWM device node under TCSR (Rob Herring)
> >> 
> >> v5:
> >> 
> >> Use &tcsr_q6 syscon to access registers (Bjorn Andersson)
> >> 
> >> Address Uwe Kleine-König review comments:
> >> 
> >>   Implement .get_state()
> >> 
> >>   Add IPQ_PWM_ prefix to local macros
> >> 
> >>   Use GENMASK/BIT/FIELD_PREP for register fields access
> >> 
> >>   Make type of config_div_and_duty() parameters consistent
> >> 
> >>   Derive IPQ_PWM_MIN_PERIOD_NS from IPQ_PWM_CLK_SRC_FREQ
> >> 
> >>   Integrate enable/disable into config_div_and_duty() to save register read,
> >>   and reduce frequency glitch on update
> >> 
> >>   Use min() instead of min_t()
> >> 
> >>   Fix comment format
> >> 
> >>   Use dev_err_probe() to indicate probe step failure
> >> 
> >>   Add missing clk_disable_unprepare() in .remove
> >> 
> >>   Don't set .owner
> >> 
> >> v4:
> >> 
> >>   Use div64_u64() to fix link for 32-bit targets ((kernel test robot
> >>   <lkp@intel.com>, Uwe Kleine-König)
> >> 
> >> v3:
> >> 
> >>   s/qcom,pwm-ipq6018/qcom,ipq6018-pwm/ (Rob Herring)
> >> 
> >>   Fix integer overflow on 32-bit targets (kernel test robot <lkp@intel.com>)
> >> 
> >> v2:
> >> 
> >> Address Uwe Kleine-König review comments:
> >> 
> >>   Fix period calculation when out of range
> >> 
> >>   Don't set period larger than requested
> >> 
> >>   Remove PWM disable on configuration change
> >> 
> >>   Implement .apply instead of non-atomic .config/.enable/.disable
> >> 
> >>   Don't modify PWM on .request/.free
> >> 
> >>   Check pwm_div underflow
> >> 
> >>   Fix various code and comment formatting issues
> >> 
> >> Other changes:
> >> 
> >>   Use u64 divisor safe division
> >> 
> >>   Remove now empty .request/.free
> >> ---
> >>  drivers/pwm/Kconfig   |  12 ++
> >>  drivers/pwm/Makefile  |   1 +
> >>  drivers/pwm/pwm-ipq.c | 275 ++++++++++++++++++++++++++++++++++++++++++
> >>  3 files changed, 288 insertions(+)
> >>  create mode 100644 drivers/pwm/pwm-ipq.c
> >> 
> >> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> >> index 21e3b05a5153..e39718137ecd 100644
> >> --- a/drivers/pwm/Kconfig
> >> +++ b/drivers/pwm/Kconfig
> >> @@ -260,6 +260,18 @@ config PWM_INTEL_LGM
> >>  	  To compile this driver as a module, choose M here: the module
> >>  	  will be called pwm-intel-lgm.
> >>  
> >> +config PWM_IPQ
> >> +	tristate "IPQ PWM support"
> >> +	depends on ARCH_QCOM || COMPILE_TEST
> >> +	depends on HAVE_CLK && HAS_IOMEM
> >> +	help
> >> +	  Generic PWM framework driver for IPQ PWM block which supports
> >> +	  4 pwm channels. Each of the these channels can be configured
> >> +	  independent of each other.
> >> +
> >> +	  To compile this driver as a module, choose M here: the module
> >> +	  will be called pwm-ipq.
> >> +
> >>  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 708840b7fba8..7402feae4b36 100644
> >> --- a/drivers/pwm/Makefile
> >> +++ b/drivers/pwm/Makefile
> >> @@ -22,6 +22,7 @@ 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-$(CONFIG_PWM_IPQ)		+= pwm-ipq.o
> >>  obj-$(CONFIG_PWM_IQS620A)	+= pwm-iqs620a.o
> >>  obj-$(CONFIG_PWM_JZ4740)	+= pwm-jz4740.o
> >>  obj-$(CONFIG_PWM_KEEMBAY)	+= pwm-keembay.o
> >> diff --git a/drivers/pwm/pwm-ipq.c b/drivers/pwm/pwm-ipq.c
> >> new file mode 100644
> >> index 000000000000..3764010808f0
> >> --- /dev/null
> >> +++ b/drivers/pwm/pwm-ipq.c
> >> @@ -0,0 +1,275 @@
> >> +// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
> >> +/*
> >> + * Copyright (c) 2016-2017, 2020 The Linux Foundation. All rights reserved.
> >> + */
> >> +
> >> +#include <linux/module.h>
> >> +#include <linux/platform_device.h>
> >> +#include <linux/pwm.h>
> >> +#include <linux/clk.h>
> >> +#include <linux/io.h>
> >> +#include <linux/of.h>
> >> +#include <linux/math64.h>
> >> +#include <linux/of_device.h>
> >> +#include <linux/bitfield.h>
> >> +
> >> +/* The frequency range supported is 1 Hz to clock rate */
> >> +#define IPQ_PWM_MAX_PERIOD_NS	((u64)NSEC_PER_SEC)
> >> +
> >> +/*
> >> + * The max value specified for each field is based on the number of bits
> >> + * in the pwm control register for that field
> >> + */
> >> +#define IPQ_PWM_MAX_DIV		0xFFFF
> >> +
> >> +/*
> >> + * Two 32-bit registers for each PWM: REG0, and REG1.
> >> + * Base offset for PWM #i is at 8 * #i.
> >> + */
> >> +#define IPQ_PWM_REG0			0 /*PWM_DIV PWM_HI*/
> >> +#define IPQ_PWM_REG0_PWM_DIV		GENMASK(15, 0)
> >> +#define IPQ_PWM_REG0_HI_DURATION	GENMASK(31, 16)
> >
> > PWM_HI in the comment of IPQ_PWM_REG0 vs. HI_DURATION? Should this
> > match? I'd say the comment is redundant.
> >
> >> +#define IPQ_PWM_REG1			4 /*ENABLE UPDATE PWM_PRE_DIV*/
> >> +#define IPQ_PWM_REG1_PRE_DIV		GENMASK(15, 0)
> >> +/*
> >> + * Enable bit is set to enable output toggling in pwm device.
> >> + * Update bit is set to reflect the changed divider and high duration
> >> + * values in register.
> >> + */
> >> +#define IPQ_PWM_REG1_UPDATE		BIT(30)
> >> +#define IPQ_PWM_REG1_ENABLE		BIT(31)
> >> +
> >> +
> >> +struct ipq_pwm_chip {
> >> +	struct pwm_chip chip;
> >> +	struct clk *clk;
> >> +	void __iomem *mem;
> >> +};
> >> +
> >> +static struct ipq_pwm_chip *ipq_pwm_from_chip(struct pwm_chip *chip)
> >> +{
> >> +	return container_of(chip, struct ipq_pwm_chip, chip);
> >> +}
> >> +
> >> +static unsigned int ipq_pwm_reg_read(struct pwm_device *pwm, unsigned int reg)
> >> +{
> >> +	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(pwm->chip);
> >> +	unsigned int off = 8 * pwm->hwpwm + reg;
> >> +
> >> +	return readl(ipq_chip->mem + off);
> >> +}
> >> +
> >> +static void ipq_pwm_reg_write(struct pwm_device *pwm, unsigned int reg,
> >> +			      unsigned int val)
> >> +{
> >> +	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(pwm->chip);
> >> +	unsigned int off = 8 * pwm->hwpwm + reg;
> >> +
> >> +	writel(val, ipq_chip->mem + off);
> >> +}
> >> +
> >> +static void config_div_and_duty(struct pwm_device *pwm, unsigned int pre_div,
> >> +			unsigned int pwm_div, unsigned long rate, u64 duty_ns,
> >> +			bool enable)
> >> +{
> >> +	unsigned long hi_dur;
> >> +	unsigned long val = 0;
> >> +
> >> +	/*
> >> +	 * high duration = pwm duty * (pwm div + 1)
> >> +	 * pwm duty = duty_ns / period_ns
> >> +	 */
> >> +	hi_dur = div64_u64(duty_ns * rate, (pre_div + 1) * NSEC_PER_SEC);
> >> +
> >> +	val = FIELD_PREP(IPQ_PWM_REG0_HI_DURATION, hi_dur) |
> >> +		FIELD_PREP(IPQ_PWM_REG0_PWM_DIV, pwm_div);
> >> +	ipq_pwm_reg_write(pwm, IPQ_PWM_REG0, val);
> >> +
> >> +	val = FIELD_PREP(IPQ_PWM_REG1_PRE_DIV, pre_div);
> >> +	ipq_pwm_reg_write(pwm, IPQ_PWM_REG1, val);
> >> +
> >> +	/* PWM enable toggle needs a separate write to REG1 */
> >> +	val |= IPQ_PWM_REG1_UPDATE;
> >> +	if (enable)
> >> +		val |= IPQ_PWM_REG1_ENABLE;
> >> +	ipq_pwm_reg_write(pwm, IPQ_PWM_REG1, val);
> >> +}
> >> +
> >> +static int ipq_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> >> +			 const struct pwm_state *state)
> >> +{
> >> +	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(chip);
> >> +	unsigned int pre_div, pwm_div, best_pre_div, best_pwm_div;
> >> +	unsigned long rate = clk_get_rate(ipq_chip->clk);
> >> +	u64 period_ns, duty_ns, period_rate;
> >> +	u64 min_diff;
> >> +
> >> +	if (state->polarity != PWM_POLARITY_NORMAL)
> >> +		return -EINVAL;
> >> +
> >> +	if (state->period < div64_u64(NSEC_PER_SEC, rate))
> >> +		return -ERANGE;
> >
> > NSEC_PER_SEC / rate is the smallest period you can achieve, right?
> > Consider rate = 33333 (Hz), then the minimal period is
> > 30000.30000300003 ns. So you should refuse a request to configure
> > state->period = 30000, but as div64_u64(1000000000, 33333) is 30000 you
> > don't.
> >
> >> +	period_ns = min(state->period, IPQ_PWM_MAX_PERIOD_NS);
> >> +	duty_ns = min(state->duty_cycle, period_ns);
> >> +
> >> +	/*
> >> +	 * period_ns is 1G or less. As long as rate is less than 16 GHz this
> >> +	 * does not overflow.
> >
> > Well, rate cannot be bigger than 4294967295 because an unsigned long
> > cannot hold a bigger value.
> 
> On 64-bit systems __SIZEOF_LONG__ is 8, which can hold more than 2^32.

Ah right, then I suggest to check that in code to make it more explicit
than in a comment.

> >> +	 */
> >> +	period_rate = period_ns * rate;
> >> +	best_pre_div = IPQ_PWM_MAX_DIV;
> >> +	best_pwm_div = IPQ_PWM_MAX_DIV;
> >> +	/* Initial pre_div value such that pwm_div < IPQ_PWM_MAX_DIV */
> 
> Note this comment.

<= ?

> 
> >> +	pre_div = div64_u64(period_rate,
> >> +			(u64)NSEC_PER_SEC * (IPQ_PWM_MAX_DIV + 1));
> >
> > Hmmm, we want 
> >
> > 	(pre_div + 1) * (pwm_div + 1) * NSEC_PER_SEC
> > 	-------------------------------------------- <= period_ns
> > 	                  rate
> >
> > , right? Resolving that for pre_div this gives:
> >
> > 	                period_ns * rate
> > 	pre_div <= ----------------------------
> > 	           NSEC_PER_SEC * (pwm_div + 1)
> >
> > The term on the right hand side is maximal for pwm_div == 0 so the
> > possible values for pre_div are
> >
> > 	0 ... min(div64_u64(period_rate / NSEC_PER_SEC), IPQ_PWM_MAX_DIV)
> >
> > isn't it?
> 
> I don't think so. pre_div == 0 will produce pwm_div larger than
> IPQ_PWM_MAX_DIV for a large period_rate value. The initial pre_div here is the
> smallest value that produces pwm_div within it limit.

Ah, got your reasoning. If a pre_div is picked that is smaller than the
value you calculate, a bigger pre_div results in a better approximation.

What strikes me is that if you pick a smaller pre_div, you can still use
pwm_div = IPQ_PWM_MAX_DIV which yields an allowed setting. So while your
argument is right, I'd need a better comment to actually understand it.
Something like:

	/*
	 * We don't need to consider pre_div values smaller than
	 *
	 *                              period_rate
	 *  pre_div_min := ------------------------------------
	 *                 NSEC_PER_SEC * (IPQ_PWM_MAX_DIV + 1)
	 *
	 * because pre_div = pre_div_min results in a better
	 * approximation.
	 */


> > If so, your algorithm is wrong as you're iterating over
> >
> > 	div64_u64(period_rate, NSEC_PER_SEC * (IPQ_PWM_MAX_DIV + 1)) ... IPQ_PWM_MAX_DIV
> 
> The loop stops when pre_div > pwm_div. That should be before pre_div ==
> IPQ_PWM_MAX_DIV because pwm_div <= IPQ_PWM_MAX_DIV. Should I put the pre_div >
> pwm_div condition directly in the for statement?

OK, moving the check isn't necessary.

> > The task here is to calculate the biggest pwm_div for a given pre_div
> > such that
> >
> >
> > 	(pre_div + 1) * (pwm_div + 1) * NSEC_PER_SEC
> > 	-------------------------------------------- <= period_ns
> > 	                   rate
> >
> > right?
> >
> > This is equivalent to:
> >
> > 	                  period_ns * rate
> > 	pre_div <= ---------------------------- - 1
> > 	           (pre_div + 1) * NSEC_PER_SEC
> >
> > As pre_div is integer, rounding down should be fine?!
> 
> I can't follow. With round down (as in v8) the result is always:
> 
>   NSEC_PER_SEC * (pre_div + 1) * (pwm_div + 1) <= period_rate

Yes, that's the condition that a valid configuration should fulfill
because then the configured period is never bigger than the requested
period.
 
> As a result, 'diff' calculation below will always produce diff <= 0. When
> there is no diff == 0 result (bingo) we get IPQ_PWM_MAX_DIV in both best_
> values at the end of the loop.

Looking again, your check is wrong. I think you need:

	diff = period_rate - NSEC_PER_SEC * (pre_div + 1) * (pwm_div + 1)

. Given the calculations for pre_div and pwm_div this should never be
negative and you should pick values that minimize diff.

> Do we actually need diff > 0 in the condition below?
> 
> >> +		/*
> >> +		 * pre_div and pwm_div values swap produces the same
> >> +		 * result. This loop goes over all pre_div <= pwm_div
> >> +		 * combinations. The rest are equivalent.
> >> +		 */
> >
> > I'd write:
> >
> > 	/*
> > 	 * Swapping values for pre_div and pwm_div produces the same
> > 	 * period length. So we can skip all settings with pre_div <
> > 	 * pwm_div which results in bigger constraints for selecting the
> > 	 * duty_cycle than with the two values swapped.
> > 	 */
> 
> I'll take your wording with inverted inequality sign.

Right.

Looking forward to your next iteration.

Best regards
Uwe
Baruch Siach Jan. 25, 2022, 4:22 p.m. UTC | #4
Hi Uwe,

On Tue, Jan 25 2022, Uwe Kleine-König wrote:
> On Tue, Jan 25, 2022 at 03:03:08PM +0200, Baruch Siach wrote:
>> On Wed, Jan 19 2022, Uwe Kleine-König wrote:
>> > The task here is to calculate the biggest pwm_div for a given pre_div
>> > such that
>> >
>> >
>> > 	(pre_div + 1) * (pwm_div + 1) * NSEC_PER_SEC
>> > 	-------------------------------------------- <= period_ns
>> > 	                   rate
>> >
>> > right?
>> >
>> > This is equivalent to:
>> >
>> > 	                  period_ns * rate
>> > 	pre_div <= ---------------------------- - 1
>> > 	           (pre_div + 1) * NSEC_PER_SEC
>> >
>> > As pre_div is integer, rounding down should be fine?!
>> 
>> I can't follow. With round down (as in v8) the result is always:
>> 
>>   NSEC_PER_SEC * (pre_div + 1) * (pwm_div + 1) <= period_rate
>
> Yes, that's the condition that a valid configuration should fulfill
> because then the configured period is never bigger than the requested
> period.
>  
>> As a result, 'diff' calculation below will always produce diff <= 0. When
>> there is no diff == 0 result (bingo) we get IPQ_PWM_MAX_DIV in both best_
>> values at the end of the loop.
>
> Looking again, your check is wrong. I think you need:
>
> 	diff = period_rate - NSEC_PER_SEC * (pre_div + 1) * (pwm_div + 1)
>
> . Given the calculations for pre_div and pwm_div this should never be
> negative and you should pick values that minimize diff.

So, if I understand correctly, you suggest to leave round up as in v10,
and invert the diff calculation. Is that correct?

Thanks,
baruch
Uwe Kleine-König Jan. 25, 2022, 5:15 p.m. UTC | #5
Hello Baruch,

On Tue, Jan 25, 2022 at 06:22:45PM +0200, Baruch Siach wrote:
> On Tue, Jan 25 2022, Uwe Kleine-König wrote:
> > On Tue, Jan 25, 2022 at 03:03:08PM +0200, Baruch Siach wrote:
> >> On Wed, Jan 19 2022, Uwe Kleine-König wrote:
> >> > The task here is to calculate the biggest pwm_div for a given pre_div
> >> > such that
> >> >
> >> >
> >> > 	(pre_div + 1) * (pwm_div + 1) * NSEC_PER_SEC
> >> > 	-------------------------------------------- <= period_ns
> >> > 	                   rate
> >> >
> >> > right?
> >> >
> >> > This is equivalent to:
> >> >
> >> > 	                  period_ns * rate
> >> > 	pre_div <= ---------------------------- - 1
> >> > 	           (pre_div + 1) * NSEC_PER_SEC
> >> >
> >> > As pre_div is integer, rounding down should be fine?!
> >> 
> >> I can't follow. With round down (as in v8) the result is always:
> >> 
> >>   NSEC_PER_SEC * (pre_div + 1) * (pwm_div + 1) <= period_rate
> >
> > Yes, that's the condition that a valid configuration should fulfill
> > because then the configured period is never bigger than the requested
> > period.
> >  
> >> As a result, 'diff' calculation below will always produce diff <= 0. When
> >> there is no diff == 0 result (bingo) we get IPQ_PWM_MAX_DIV in both best_
> >> values at the end of the loop.
> >
> > Looking again, your check is wrong. I think you need:
> >
> > 	diff = period_rate - NSEC_PER_SEC * (pre_div + 1) * (pwm_div + 1)
> >
> > . Given the calculations for pre_div and pwm_div this should never be
> > negative and you should pick values that minimize diff.
> 
> So, if I understand correctly, you suggest to leave round up as in v10,
> and invert the diff calculation. Is that correct?

If you agree that this results in the intended setting and keeps dmesg
clean even with PWM_DEBUG enabled: yes.

Best regards
Uwe
diff mbox series

Patch

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 21e3b05a5153..e39718137ecd 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -260,6 +260,18 @@  config PWM_INTEL_LGM
 	  To compile this driver as a module, choose M here: the module
 	  will be called pwm-intel-lgm.
 
+config PWM_IPQ
+	tristate "IPQ PWM support"
+	depends on ARCH_QCOM || COMPILE_TEST
+	depends on HAVE_CLK && HAS_IOMEM
+	help
+	  Generic PWM framework driver for IPQ PWM block which supports
+	  4 pwm channels. Each of the these channels can be configured
+	  independent of each other.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called pwm-ipq.
+
 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 708840b7fba8..7402feae4b36 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -22,6 +22,7 @@  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-$(CONFIG_PWM_IPQ)		+= pwm-ipq.o
 obj-$(CONFIG_PWM_IQS620A)	+= pwm-iqs620a.o
 obj-$(CONFIG_PWM_JZ4740)	+= pwm-jz4740.o
 obj-$(CONFIG_PWM_KEEMBAY)	+= pwm-keembay.o
diff --git a/drivers/pwm/pwm-ipq.c b/drivers/pwm/pwm-ipq.c
new file mode 100644
index 000000000000..3764010808f0
--- /dev/null
+++ b/drivers/pwm/pwm-ipq.c
@@ -0,0 +1,275 @@ 
+// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
+/*
+ * Copyright (c) 2016-2017, 2020 The Linux Foundation. All rights reserved.
+ */
+
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+#include <linux/clk.h>
+#include <linux/io.h>
+#include <linux/of.h>
+#include <linux/math64.h>
+#include <linux/of_device.h>
+#include <linux/bitfield.h>
+
+/* The frequency range supported is 1 Hz to clock rate */
+#define IPQ_PWM_MAX_PERIOD_NS	((u64)NSEC_PER_SEC)
+
+/*
+ * The max value specified for each field is based on the number of bits
+ * in the pwm control register for that field
+ */
+#define IPQ_PWM_MAX_DIV		0xFFFF
+
+/*
+ * Two 32-bit registers for each PWM: REG0, and REG1.
+ * Base offset for PWM #i is at 8 * #i.
+ */
+#define IPQ_PWM_REG0			0 /*PWM_DIV PWM_HI*/
+#define IPQ_PWM_REG0_PWM_DIV		GENMASK(15, 0)
+#define IPQ_PWM_REG0_HI_DURATION	GENMASK(31, 16)
+
+#define IPQ_PWM_REG1			4 /*ENABLE UPDATE PWM_PRE_DIV*/
+#define IPQ_PWM_REG1_PRE_DIV		GENMASK(15, 0)
+/*
+ * Enable bit is set to enable output toggling in pwm device.
+ * Update bit is set to reflect the changed divider and high duration
+ * values in register.
+ */
+#define IPQ_PWM_REG1_UPDATE		BIT(30)
+#define IPQ_PWM_REG1_ENABLE		BIT(31)
+
+
+struct ipq_pwm_chip {
+	struct pwm_chip chip;
+	struct clk *clk;
+	void __iomem *mem;
+};
+
+static struct ipq_pwm_chip *ipq_pwm_from_chip(struct pwm_chip *chip)
+{
+	return container_of(chip, struct ipq_pwm_chip, chip);
+}
+
+static unsigned int ipq_pwm_reg_read(struct pwm_device *pwm, unsigned int reg)
+{
+	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(pwm->chip);
+	unsigned int off = 8 * pwm->hwpwm + reg;
+
+	return readl(ipq_chip->mem + off);
+}
+
+static void ipq_pwm_reg_write(struct pwm_device *pwm, unsigned int reg,
+			      unsigned int val)
+{
+	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(pwm->chip);
+	unsigned int off = 8 * pwm->hwpwm + reg;
+
+	writel(val, ipq_chip->mem + off);
+}
+
+static void config_div_and_duty(struct pwm_device *pwm, unsigned int pre_div,
+			unsigned int pwm_div, unsigned long rate, u64 duty_ns,
+			bool enable)
+{
+	unsigned long hi_dur;
+	unsigned long val = 0;
+
+	/*
+	 * high duration = pwm duty * (pwm div + 1)
+	 * pwm duty = duty_ns / period_ns
+	 */
+	hi_dur = div64_u64(duty_ns * rate, (pre_div + 1) * NSEC_PER_SEC);
+
+	val = FIELD_PREP(IPQ_PWM_REG0_HI_DURATION, hi_dur) |
+		FIELD_PREP(IPQ_PWM_REG0_PWM_DIV, pwm_div);
+	ipq_pwm_reg_write(pwm, IPQ_PWM_REG0, val);
+
+	val = FIELD_PREP(IPQ_PWM_REG1_PRE_DIV, pre_div);
+	ipq_pwm_reg_write(pwm, IPQ_PWM_REG1, val);
+
+	/* PWM enable toggle needs a separate write to REG1 */
+	val |= IPQ_PWM_REG1_UPDATE;
+	if (enable)
+		val |= IPQ_PWM_REG1_ENABLE;
+	ipq_pwm_reg_write(pwm, IPQ_PWM_REG1, val);
+}
+
+static int ipq_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
+			 const struct pwm_state *state)
+{
+	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(chip);
+	unsigned int pre_div, pwm_div, best_pre_div, best_pwm_div;
+	unsigned long rate = clk_get_rate(ipq_chip->clk);
+	u64 period_ns, duty_ns, period_rate;
+	u64 min_diff;
+
+	if (state->polarity != PWM_POLARITY_NORMAL)
+		return -EINVAL;
+
+	if (state->period < div64_u64(NSEC_PER_SEC, rate))
+		return -ERANGE;
+
+	period_ns = min(state->period, IPQ_PWM_MAX_PERIOD_NS);
+	duty_ns = min(state->duty_cycle, period_ns);
+
+	/*
+	 * period_ns is 1G or less. As long as rate is less than 16 GHz this
+	 * does not overflow.
+	 */
+	period_rate = period_ns * rate;
+	best_pre_div = IPQ_PWM_MAX_DIV;
+	best_pwm_div = IPQ_PWM_MAX_DIV;
+	/* Initial pre_div value such that pwm_div < IPQ_PWM_MAX_DIV */
+	pre_div = div64_u64(period_rate,
+			(u64)NSEC_PER_SEC * (IPQ_PWM_MAX_DIV + 1));
+	min_diff = period_rate;
+
+	for (; pre_div <= IPQ_PWM_MAX_DIV; pre_div++) {
+		long long diff;
+
+		pwm_div = DIV64_U64_ROUND_UP(period_rate,
+				(u64)NSEC_PER_SEC * (pre_div + 1));
+		/* pwm_div is unsigned; the check below catches underflow */
+		pwm_div--;
+
+		/*
+		 * pre_div and pwm_div values swap produces the same
+		 * result. This loop goes over all pre_div <= pwm_div
+		 * combinations. The rest are equivalent.
+		 */
+		if (pre_div > pwm_div)
+			break;
+
+		/*
+		 * Make sure we can do 100% duty cycle where
+		 * hi_dur == pwm_div + 1
+		 */
+		if (pwm_div > IPQ_PWM_MAX_DIV - 1)
+			continue;
+
+		diff = ((uint64_t)NSEC_PER_SEC * (pre_div + 1) * (pwm_div + 1))
+			- period_rate;
+
+		if (diff < 0) /* period larger than requested */
+			continue;
+		if (diff == 0) { /* bingo */
+			best_pre_div = pre_div;
+			best_pwm_div = pwm_div;
+			break;
+		}
+		if (diff < min_diff) {
+			min_diff = diff;
+			best_pre_div = pre_div;
+			best_pwm_div = pwm_div;
+		}
+	}
+
+	/* config divider values for the closest possible frequency */
+	config_div_and_duty(pwm, best_pre_div, best_pwm_div,
+			    rate, duty_ns, state->enabled);
+
+	return 0;
+}
+
+static void ipq_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
+			      struct pwm_state *state)
+{
+	struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(chip);
+	unsigned long rate = clk_get_rate(ipq_chip->clk);
+	unsigned int pre_div, pwm_div, hi_dur;
+	u64 effective_div, hi_div;
+	u32 reg0, reg1;
+
+	reg0 = ipq_pwm_reg_read(pwm, IPQ_PWM_REG0);
+	reg1 = ipq_pwm_reg_read(pwm, IPQ_PWM_REG1);
+
+	state->polarity = PWM_POLARITY_NORMAL;
+	state->enabled = reg1 & IPQ_PWM_REG1_ENABLE;
+
+	pwm_div = FIELD_GET(IPQ_PWM_REG0_PWM_DIV, reg0);
+	hi_dur = FIELD_GET(IPQ_PWM_REG0_HI_DURATION, reg0);
+	pre_div = FIELD_GET(IPQ_PWM_REG1_PRE_DIV, reg1);
+
+	/* No overflow here, both pre_div and pwm_div <= 0xffff */
+	effective_div = (u64)(pre_div + 1) * (pwm_div + 1);
+	state->period = DIV64_U64_ROUND_UP(effective_div * NSEC_PER_SEC, rate);
+
+	hi_div = hi_dur * (pre_div + 1);
+	state->duty_cycle = div64_u64(hi_div * NSEC_PER_SEC, rate);
+}
+
+static const struct pwm_ops ipq_pwm_ops = {
+	.apply = ipq_pwm_apply,
+	.get_state = ipq_pwm_get_state,
+	.owner = THIS_MODULE,
+};
+
+static int ipq_pwm_probe(struct platform_device *pdev)
+{
+	struct ipq_pwm_chip *pwm;
+	struct device *dev = &pdev->dev;
+	int ret;
+
+	pwm = devm_kzalloc(dev, sizeof(*pwm), GFP_KERNEL);
+	if (!pwm)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, pwm);
+
+	pwm->mem = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(pwm->mem))
+		return dev_err_probe(dev, PTR_ERR(pwm->mem),
+				"regs map failed");
+
+	pwm->clk = devm_clk_get(dev, NULL);
+	if (IS_ERR(pwm->clk))
+		return dev_err_probe(dev, PTR_ERR(pwm->clk),
+				"failed to get clock");
+
+	ret = clk_prepare_enable(pwm->clk);
+	if (ret)
+		return dev_err_probe(dev, ret, "clock enable failed");
+
+	pwm->chip.dev = dev;
+	pwm->chip.ops = &ipq_pwm_ops;
+	pwm->chip.npwm = 4;
+
+	ret = pwmchip_add(&pwm->chip);
+	if (ret < 0) {
+		dev_err_probe(dev, ret, "pwmchip_add() failed\n");
+		clk_disable_unprepare(pwm->clk);
+	}
+
+	return ret;
+}
+
+static int ipq_pwm_remove(struct platform_device *pdev)
+{
+	struct ipq_pwm_chip *pwm = platform_get_drvdata(pdev);
+
+	pwmchip_remove(&pwm->chip);
+	clk_disable_unprepare(pwm->clk);
+
+	return 0;
+}
+
+static const struct of_device_id pwm_ipq_dt_match[] = {
+	{ .compatible = "qcom,ipq6018-pwm", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, pwm_ipq_dt_match);
+
+static struct platform_driver ipq_pwm_driver = {
+	.driver = {
+		.name = "ipq-pwm",
+		.of_match_table = pwm_ipq_dt_match,
+	},
+	.probe = ipq_pwm_probe,
+	.remove = ipq_pwm_remove,
+};
+
+module_platform_driver(ipq_pwm_driver);
+
+MODULE_LICENSE("Dual BSD/GPL");