Re: [PATCH 1/3] pwm: driver for qualcomm ipq6018 pwm block

[Devi Priya <quic_devipriy@quicinc.com>]

On 2/7/2022 3:00 PM, 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>
> ---
> v11:
> 
Hi Baruch,

Just curious to know if you have plans to post the next revision!

Thanks,
Devi Priya

> Address comment from Uwe Kleine-König:
> 
>    Drop redundant registers field comments
> 
>    Fix period limit check in .apply
> 
>    Clarify the comment explaining skip of pre_div > pwm_div values
> 
>    Add explicit check for clock rate within limit
> 
>    Add comment explaining the selection of initial pre_div
> 
>    Use pwm_div division with remainder instead of separate diff calculation
> 
>    Round up duty_cycle calculation in .get_state
> 
> 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 | 281 ++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 294 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..994027290bcb
> --- /dev/null
> +++ b/drivers/pwm/pwm-ipq.c
> @@ -0,0 +1,281 @@
> +// 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>
> +#include <linux/units.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
> +#define IPQ_PWM_REG0_PWM_DIV		GENMASK(15, 0)
> +#define IPQ_PWM_REG0_HI_DURATION	GENMASK(31, 16)
> +
> +#define IPQ_PWM_REG1			4
> +#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_ROUND_UP(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,
> +	 * period_rate does not overflow. Make that explicit.
> +	 */
> +	if (rate > 16ULL * GIGA)
> +		return -EINVAL;
> +	period_rate = period_ns * rate;
> +	best_pre_div = IPQ_PWM_MAX_DIV;
> +	best_pwm_div = IPQ_PWM_MAX_DIV;
> +	/*
> +	 * 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.
> +	 */
> +	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++) {
> +		u64 remainder;
> +
> +		pwm_div = div64_u64_rem(period_rate,
> +				(u64)NSEC_PER_SEC * (pre_div + 1), &remainder);
> +		/* pwm_div is unsigned; the check below catches underflow */
> +		pwm_div--;
> +
> +		/*
> +		 * 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;
> +
> +		if (remainder < min_diff) {
> +			best_pre_div = pre_div;
> +			best_pwm_div = pwm_div;
> +			min_diff = remainder;
> +
> +			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_ROUND_UP(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");