Re: [v8 2/2] pwm: Add Aspeed ast2600 PWM support

From: Billy Tsai
Date: Fri Jul 09 2021 - 02:00:56 EST

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On 2021/7/9, 1:40 PM, "Billy Tsai" <billy_tsai@xxxxxxxxxxxxxx> wrote:

> On Tue, Jun 08, 2021 at 02:46:58PM +0800, Billy Tsai wrote:
> >> This patch add the support of PWM controller which can be found at aspeed
> >> ast2600 soc. The pwm supoorts up to 16 channels and it's part function
> >> of multi-function device "pwm-tach controller".
> >>
> >> Signed-off-by: Billy Tsai <billy_tsai@xxxxxxxxxxxxxx>
> >> ---
> >> drivers/pwm/Kconfig | 9 +
> >> drivers/pwm/Makefile | 1 +
> >> drivers/pwm/pwm-aspeed-ast2600.c | 311 +++++++++++++++++++++++++++++++
> >> 3 files changed, 321 insertions(+)
> >> create mode 100644 drivers/pwm/pwm-aspeed-ast2600.c
> >>
> >> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> >> index 63be5362fd3a..a5aac3ca4ac7 100644
> >> --- a/drivers/pwm/Kconfig
> >> +++ b/drivers/pwm/Kconfig
> >> @@ -51,6 +51,15 @@ config PWM_AB8500
> >> To compile this driver as a module, choose M here: the module
> >> will be called pwm-ab8500.
> >>
> >> +config PWM_ASPEED_AST2600
> >> + tristate "Aspeed ast2600 PWM support"
> >> + depends on ARCH_ASPEED || COMPILE_TEST
> >> + help
> >> + This driver provides support for Aspeed ast2600 PWM controllers.
> >> +
> >> + To compile this driver as a module, choose M here: the module
> >> + will be called pwm-aspeed-ast2600.
> >> +
> >> config PWM_ATMEL
> >> tristate "Atmel PWM support"
> >> depends on OF
> >> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> >> index cbdcd55d69ee..ada454f9129a 100644
> >> --- a/drivers/pwm/Makefile
> >> +++ b/drivers/pwm/Makefile
> >> @@ -2,6 +2,7 @@
> >> obj-$(CONFIG_PWM) += core.o
> >> obj-$(CONFIG_PWM_SYSFS) += sysfs.o
> >> obj-$(CONFIG_PWM_AB8500) += pwm-ab8500.o
> >> +obj-$(CONFIG_PWM_ASPEED_AST2600) += pwm-aspeed-ast2600.o
> >> obj-$(CONFIG_PWM_ATMEL) += pwm-atmel.o
> >> obj-$(CONFIG_PWM_ATMEL_HLCDC_PWM) += pwm-atmel-hlcdc.o
> >> obj-$(CONFIG_PWM_ATMEL_TCB) += pwm-atmel-tcb.o
> >> diff --git a/drivers/pwm/pwm-aspeed-ast2600.c b/drivers/pwm/pwm-aspeed-ast2600.c
> >> new file mode 100644
> >> index 000000000000..6ea0f7eb311f
> >> --- /dev/null
> >> +++ b/drivers/pwm/pwm-aspeed-ast2600.c
> >> @@ -0,0 +1,311 @@
> >> +// SPDX-License-Identifier: GPL-2.0-or-later
> >> +/*
> >> + * Copyright (C) 2021 Aspeed Technology Inc.
> >> + *
> >> + * PWM controller driver for Aspeed ast2600 SoCs.
> >> + * This drivers doesn't support earlier version of the IP.
> >> + *
> >> + * The formula of pwm period duration:
> >> + * period duration = ((DIV_L + 1) * BIT(DIV_H) * (PERIOD + 1)) / input-clk
> >> + *
> >> + * The software driver fixes the period to 255, which causes the high-frequency
> >> + * precision of the PWM to be coarse, in exchange for the fineness of the duty cycle.
> >> + *
> >> + * Register usage:
> >> + * PIN_ENABLE: When it is unset the pwm controller will always output low to the extern.
> >> + * Use to determine whether the PWM channel is enabled or disabled
> >> + * CLK_ENABLE: When it is unset the pwm controller will reset the duty counter to 0 and
> >> + * output low to the PIN_ENABLE mux after that the driver can still change the pwm period
> >> + * and duty and the value will apply when CLK_ENABLE be set again.
> >> + * Use to determine whether duty_cycle bigger than 0.
> >> + * PWM_ASPEED_CTRL_INVERSE: When it is toggled the output value will inverse immediately.
> >> + * PWM_ASPEED_DUTY_CYCLE_FALLING_POINT/PWM_ASPEED_DUTY_CYCLE_RISING_POINT: When these two
> >> + * values are equal it means the duty cycle = 100%.
> >> + *
> >> + * Limitations:
> >> + * - When changing both duty cycle and period, we cannot prevent in
> >> + * software that the output might produce a period with mixed
> >> + * settings.
> >> + * - Disabling the PWM doesn't complete the current period.
> >> + *
> >> + * Improvements:
> >> + * - When only changing one of duty cycle or period, our pwm controller will not
> >> + * generate the glitch, the configure will change at next cycle of pwm.
> >> + * This improvement can disable/enable through PWM_ASPEED_CTRL_DUTY_SYNC_DISABLE.
> >> + */
> >> +
> >> +#include <linux/clk.h>
> >> +#include <linux/errno.h>
> >> +#include <linux/io.h>
> >> +#include <linux/kernel.h>
> >> +#include <linux/mfd/syscon.h>
> >> +#include <linux/module.h>
> >> +#include <linux/of_platform.h>
> >> +#include <linux/of_device.h>
> >> +#include <linux/platform_device.h>
> >> +#include <linux/sysfs.h>
> >> +#include <linux/reset.h>
> >> +#include <linux/regmap.h>
> >> +#include <linux/bitfield.h>
> >> +#include <linux/slab.h>
> >> +#include <linux/pwm.h>
> >> +#include <linux/math64.h>
> >> +
> >> +/* The channel number of Aspeed pwm controller */
> >> +#define PWM_ASPEED_NR_PWMS 16
> >> +
> >> +/* PWM Control Register */
> >> +#define PWM_ASPEED_CTRL(ch) ((ch) * 0x10 + 0x00)
> >> +#define PWM_ASPEED_CTRL_LOAD_SEL_RISING_AS_WDT BIT(19)
> >> +#define PWM_ASPEED_CTRL_DUTY_LOAD_AS_WDT_ENABLE BIT(18)
> >> +#define PWM_ASPEED_CTRL_DUTY_SYNC_DISABLE BIT(17)
> >> +#define PWM_ASPEED_CTRL_CLK_ENABLE BIT(16)
> >> +#define PWM_ASPEED_CTRL_LEVEL_OUTPUT BIT(15)
> >> +#define PWM_ASPEED_CTRL_INVERSE BIT(14)
> >> +#define PWM_ASPEED_CTRL_OPEN_DRAIN_ENABLE BIT(13)
> >> +#define PWM_ASPEED_CTRL_PIN_ENABLE BIT(12)
> >> +#define PWM_ASPEED_CTRL_CLK_DIV_H GENMASK(11, 8)
> >> +#define PWM_ASPEED_CTRL_CLK_DIV_L GENMASK(7, 0)
> >> +
> >> +/* PWM Duty Cycle Register */
> >> +#define PWM_ASPEED_DUTY_CYCLE(ch) ((ch) * 0x10 + 0x04)
> >> +#define PWM_ASPEED_DUTY_CYCLE_PERIOD GENMASK(31, 24)
> >> +#define PWM_ASPEED_DUTY_CYCLE_POINT_AS_WDT GENMASK(23, 16)
> >> +#define PWM_ASPEED_DUTY_CYCLE_FALLING_POINT GENMASK(15, 8)
> >> +#define PWM_ASPEED_DUTY_CYCLE_RISING_POINT GENMASK(7, 0)
> >> +
> >> +/* PWM fixed value */
> >> +#define PWM_ASPEED_FIXED_PERIOD FIELD_MAX(PWM_ASPEED_DUTY_CYCLE_PERIOD)
> >> +
> >> +struct aspeed_pwm_data {
> >> + struct pwm_chip chip;
> >> + struct clk *clk;
> >> + struct regmap *regmap;
> >> + struct reset_control *reset;
> >> +};
> >> +
> >> +static inline struct aspeed_pwm_data *
> >> +aspeed_pwm_chip_to_data(struct pwm_chip *chip)
> >> +{
> >> + return container_of(chip, struct aspeed_pwm_data, chip);
> >> +}
> >> +
> >> +static void aspeed_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> >> + struct pwm_state *state)
> >> +{
> >> + struct device *dev = chip->dev;
> >> + struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
> >> + u32 index = pwm->hwpwm;
> >> + bool polarity, ch_en, clk_en;
> >> + u32 duty_pt, val;
> >> + unsigned long rate;
> >> + u64 div_h, div_l, clk_period;
> >> +
> >> + regmap_read(priv->regmap, PWM_ASPEED_CTRL(index), &val);
> >> + polarity = FIELD_GET(PWM_ASPEED_CTRL_INVERSE, val);
> >> + ch_en = FIELD_GET(PWM_ASPEED_CTRL_PIN_ENABLE, val);
> >> + clk_en = FIELD_GET(PWM_ASPEED_CTRL_CLK_ENABLE, val);
> >> + div_h = FIELD_GET(PWM_ASPEED_CTRL_CLK_DIV_H, val);
> >> + div_l = FIELD_GET(PWM_ASPEED_CTRL_CLK_DIV_L, val);
> >> + regmap_read(priv->regmap, PWM_ASPEED_DUTY_CYCLE(index), &val);
> >> + duty_pt = FIELD_GET(PWM_ASPEED_DUTY_CYCLE_FALLING_POINT, val);
> >> + clk_period = FIELD_GET(PWM_ASPEED_DUTY_CYCLE_PERIOD, val);
> >> +
> >> + rate = clk_get_rate(priv->clk);
> >> + state->period = DIV_ROUND_UP_ULL((u64)NSEC_PER_SEC * _BITULL(div_h) *
> >> + (div_l + 1) * (clk_period + 1),
> >> + rate);

> > Instead of _BITULL(div_h) you can just do << div_h, which reads a bit
> > easier.

>Okay, I will send patch v9 to fix it.

> > The multiplication can be up to:

> > 100000000 * (1 << 31) * (31 + 1) * (255 + 1)

> > right? This needs 71 bits and so might overflow a u64.

>No, the multiplication can be up to:

>Max(div_h) = 15
>Max(div_l) = 255
>Max(clk_period) = 255
>1000000000 * (1 << 15) * (255 + 1) * (255 + 1) < 2^64 - 1
>it doesn't overflow a u64.

> > I guess to prevent that you have to do something like SH_DIV does for a
> > u32 division:

> > u64 rem;

> > /*
> > * To calculate
> > *
> > * roundup(NSEC_PER_SEC * (div_l + 1) * (clk_period + 1) << div_h / rate)
> > *
> > * we have to jump through some hoops because the numerator
> > * might not fit into a u64. So calculate:
> > *
> > * roundup(NSEC_PER_SEC * (div_l + 1) * (clk_period + 1) / rate) << div_h
> > *
> > * and fixup for the imprecision.
> > */
> > nom = (u64)NSEC_PER_SEC * (div_l + 1) * (clk_period + 1) + (rate - 1);
> > rem = do_div(nom, rate);
> > state->period = nom << div_h + DIV_ROUND_DOWN_ULL(rem << div_h + (rate >> 1), rate);

> > You might want to double check my math here, I didn't invest the time to
> > verify myself that this is sensible but just quickly combined SH_DIV and
> > DIV_ROUND_UP_ULL.

> >> + if (clk_en && duty_pt)
> >> + state->duty_cycle = DIV_ROUND_UP_ULL(
> >> + state->period * duty_pt, clk_period + 1);

> > You're loosing precision here. You have to repeat the hoop jumping from
> > above to fix.

>I will use your method to fix it.
>Thanks

I found that I don't need to use SH_DIV here.
duty_cycle = (period * duty_pt)/(clk_period + 1)
period = (NSEC_PER_SEC * (div_l + 1) * (clk_period + 1) << div_h) / rate
So the duty_cycle = ((NSEC_PER_SEC * (div_l + 1) << div_h) * duty_pt) / rate.
And the max(duty_pt) = 255
((NSEC_PER_SEC * (div_l + 1) << div_h) * duty_pt) < 2^64 - 1.
it doesn't overflow a u64.

> > + else
> > + state->duty_cycle = clk_en ? state->period : 0;
> > + state->polarity = polarity;
> > + state->enabled = ch_en;
> > + dev_dbg(dev, "get period: %lldns, duty_cycle: %lldns", state->period,
> > + state->duty_cycle);
> > +}
> > +
> > +static int aspeed_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> > + const struct pwm_state *state)
> > +{
> > + struct device *dev = chip->dev;
> > + struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
> > + u32 index = pwm->hwpwm, duty_pt;
> > + unsigned long rate;
> > + u64 div_h, div_l, divisor;
> > + bool clk_en;
> > +
> > + dev_dbg(dev, "expect period: %lldns, duty_cycle: %lldns", state->period,
> > + state->duty_cycle);
> > +
> > + rate = clk_get_rate(priv->clk);
> > + /*
> > + * Pick the smallest value for div_h so that div_l can be the biggest
> > + * which results in a finer resolution near the target period value.
> > + */
> > + divisor = (u64)NSEC_PER_SEC * (PWM_ASPEED_FIXED_PERIOD + 1) *
> > + (FIELD_MAX(PWM_ASPEED_CTRL_CLK_DIV_L) + 1);
> > + div_h = order_base_2(DIV64_U64_ROUND_UP(rate * state->period, divisor));
> > + if (div_h > 0xf)
> > + div_h = 0xf;
> > +
> > + divisor = ((u64)NSEC_PER_SEC * (PWM_ASPEED_FIXED_PERIOD + 1)) << div_h;
> > + div_l = div64_u64(rate * state->period, divisor);
> > +
> > + if (div_l == 0)
> > + return -ERANGE;
> > +
> > + div_l -= 1;
> > +
> > + if (div_l > 255)
> > + div_l = 255;

> > I already checked that in the previous round, I assume that's fine now.

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Previous message: Uwe Kleine-König: "Re: [v8 2/2] pwm: Add Aspeed ast2600 PWM support"
In reply to: Uwe Kleine-König: "Re: [v8 2/2] pwm: Add Aspeed ast2600 PWM support"
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