RE: [PATCH V8 2/5] pwm: Add i.MX TPM PWM driver support

From: Anson Huang
Date: Thu Mar 21 2019 - 05:54:29 EST

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Hi, Uwe

Best Regards!
Anson Huang

> -----Original Message-----
> From: Uwe Kleine-KÃnig [mailto:u.kleine-koenig@xxxxxxxxxxxxxx]
> Sent: 2019å3æ21æ 17:20
> To: Anson Huang <anson.huang@xxxxxxx>
> Cc: thierry.reding@xxxxxxxxx; robh+dt@xxxxxxxxxx; mark.rutland@xxxxxxx;
> shawnguo@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx;
> festevam@xxxxxxxxx; linux@xxxxxxxxxxxxxxx; stefan@xxxxxxxx;
> otavio@xxxxxxxxxxxxxxxx; Leonard Crestez <leonard.crestez@xxxxxxx>;
> schnitzeltony@xxxxxxxxx; jan.tuerk@xxxxxxxxxxx; Robin Gong
> <yibin.gong@xxxxxxx>; linux-pwm@xxxxxxxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; dl-linux-imx <linux-imx@xxxxxxx>
> Subject: Re: [PATCH V8 2/5] pwm: Add i.MX TPM PWM driver support
>
> Hello,
>
> On Thu, Mar 21, 2019 at 12:47:57AM +0000, Anson Huang wrote:
> > i.MX7ULP has TPM(Low Power Timer/Pulse Width Modulation Module)
> > inside, it can support multiple PWM channels, all the channels share
> > same counter and period setting, but each channel can configure its
> > duty and polarity independently.
> >
> > There are several TPM modules in i.MX7ULP, the number of channels in
> > TPM modules are different, it can be read from each TPM module's PARAM
> > register.
> >
> > Signed-off-by: Anson Huang <Anson.Huang@xxxxxxx>
> > ---
> > changes since V7:
> > - improve prescale computation;
> > - improve some register definitions;
> > - remove unnecessary check for period count check;
> > - improve function parameter to use pointer instead of value;
> > ---
> > drivers/pwm/Kconfig | 11 ++
> > drivers/pwm/Makefile | 1 +
> > drivers/pwm/pwm-imx-tpm.c | 435
> > ++++++++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 447 insertions(+)
> > create mode 100644 drivers/pwm/pwm-imx-tpm.c
> >
> > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig index
> > 54f8238..3ea0391 100644
> > --- a/drivers/pwm/Kconfig
> > +++ b/drivers/pwm/Kconfig
> > @@ -210,6 +210,17 @@ config PWM_IMX27
> > To compile this driver as a module, choose M here: the module
> > will be called pwm-imx27.
> >
> > +config PWM_IMX_TPM
> > + tristate "i.MX TPM PWM support"
> > + depends on ARCH_MXC || COMPILE_TEST
> > + depends on HAVE_CLK && HAS_IOMEM
> > + help
> > + Generic PWM framework driver for i.MX7ULP TPM module, TPM's
> full
> > + name is Low Power Timer/Pulse Width Modulation Module.
> > +
> > + To compile this driver as a module, choose M here: the module
> > + will be called pwm-imx-tpm.
> > +
> > config PWM_JZ4740
> > tristate "Ingenic JZ47xx PWM support"
> > depends on MACH_INGENIC
> > diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile index
> > 448825e..c368599 100644
> > --- a/drivers/pwm/Makefile
> > +++ b/drivers/pwm/Makefile
> > @@ -19,6 +19,7 @@ obj-$(CONFIG_PWM_HIBVT) += pwm-
> hibvt.o
> > obj-$(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_JZ4740) += pwm-jz4740.o
> > obj-$(CONFIG_PWM_LP3943) += pwm-lp3943.o
> > obj-$(CONFIG_PWM_LPC18XX_SCT) += pwm-lpc18xx-sct.o
> > diff --git a/drivers/pwm/pwm-imx-tpm.c b/drivers/pwm/pwm-imx-tpm.c
> new
> > file mode 100644 index 0000000..0efea36
> > --- /dev/null
> > +++ b/drivers/pwm/pwm-imx-tpm.c
> > @@ -0,0 +1,435 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright 2018-2019 NXP.
> > + *
> > + * Limitations:
> > + * - The TPM counter and period counter are shared between
> > + * multiple channels, so all channels should use same period
> > + * settings.
>
> What about:
>
> - Not all parameters to change the period length can be changed
> atomically. The counter must be stopped to change SC.PS.
>
> - Changes to polarity cannot be latched at the time of the next period
> start.

OK.

>
> ?
>
> > + */
> > +
> > +#include <linux/bitfield.h>
> > +#include <linux/bitops.h>
> > +#include <linux/clk.h>
> > +#include <linux/err.h>
> > +#include <linux/io.h>
> > +#include <linux/log2.h>
> > +#include <linux/module.h>
> > +#include <linux/of.h>
> > +#include <linux/of_address.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/pwm.h>
> > +#include <linux/slab.h>
> > +
> > +#define PWM_IMX_TPM_PARAM 0x4
> > +#define PWM_IMX_TPM_GLOBAL 0x8
> > +#define PWM_IMX_TPM_SC 0x10
> > +#define PWM_IMX_TPM_CNT 0x14
> > +#define PWM_IMX_TPM_MOD 0x18
> > +#define PWM_IMX_TPM_CnSC(n) (0x20 + (n) * 0x8)
> > +#define PWM_IMX_TPM_CnV(n) (0x24 + (n) * 0x8)
> > +
> > +#define PWM_IMX_TPM_PARAM_CHAN GENMASK(7,
> 0)
> > +
> > +#define PWM_IMX_TPM_SC_PS GENMASK(2, 0)
> > +#define PWM_IMX_TPM_SC_CMOD GENMASK(4, 3)
> > +#define PWM_IMX_TPM_SC_CMOD_INC_EVERY_CLK
> FIELD_PREP(PWM_IMX_TPM_SC_CMOD, 1)
> > +#define PWM_IMX_TPM_SC_CPWMS BIT(5)
> > +
> > +#define PWM_IMX_TPM_CnSC_CHF BIT(7)
> > +#define PWM_IMX_TPM_CnSC_MSB BIT(5)
> > +#define PWM_IMX_TPM_CnSC_MSA BIT(4)
> > +
> > +/*
> > + * The reference manual describes this field as two separate bits.
> > +The
> > + * samantic of the two bits isn't orthogonal though, so they are
> > +treated
> > + * together as a 2-bit field here.
> > + */
> > +#define PWM_IMX_TPM_CnSC_ELS GENMASK(3, 2)
> > +#define PWM_IMX_TPM_CnSC_ELS_POLARITY_INVERSED 0x1
> > +#define PWM_IMX_TPM_CnSC_ELS_INVERSED
> FIELD_PREP(PWM_IMX_TPM_CnSC_ELS, 1)
> > +#define PWM_IMX_TPM_CnSC_ELS_NORMAL
> FIELD_PREP(PWM_IMX_TPM_CnSC_ELS, 2)
> > +
> > +
> > +#define PWM_IMX_TPM_MOD_WIDTH 16
> > +#define PWM_IMX_TPM_MOD_MOD
> GENMASK(PWM_IMX_TPM_MOD_WIDTH - 1, 0)
> > +
> > +struct imx_tpm_pwm_chip {
> > + struct pwm_chip chip;
> > + struct clk *clk;
> > + void __iomem *base;
> > + struct mutex lock;
> > + u32 user_count;
> > + u32 enable_count;
> > + u32 real_period;
> > +};
> > +
> > +struct imx_tpm_pwm_param {
> > + u8 prescale;
> > + u32 mod;
> > +};
> > +
> > +static inline struct imx_tpm_pwm_chip *to_imx_tpm_pwm_chip(struct
> > +pwm_chip *chip) {
> > + return container_of(chip, struct imx_tpm_pwm_chip, chip); }
> > +
> > +static int pwm_imx_tpm_round_state(struct pwm_chip *chip,
> > + struct imx_tpm_pwm_param *p,
> > + struct pwm_state *state,
> > + struct pwm_state *real_state)
> > +{
> > + struct imx_tpm_pwm_chip *tpm = to_imx_tpm_pwm_chip(chip);
> > + u32 rate, prescale, period_count, clock_unit;
> > + u64 tmp;
> > +
> > + rate = clk_get_rate(tpm->clk);
> > + tmp = (u64)state->period * rate;
> > + clock_unit = DIV_ROUND_CLOSEST_ULL(tmp, NSEC_PER_SEC);
> > + if (clock_unit <= PWM_IMX_TPM_MOD_MOD)
> > + prescale = 0;
> > + else
> > + prescale = ilog2(clock_unit) + 1 -
> PWM_IMX_TPM_MOD_WIDTH;
> > +
> > + if ((!FIELD_FIT(PWM_IMX_TPM_SC_PS, prescale)))
> > + return -ERANGE;
> > + p->prescale = prescale;
> > +
> > + period_count = (clock_unit + ((1 << prescale) >> 1)) >> prescale;
> > + p->mod = period_count;
> > +
> > + /* calculate real period HW can support */
> > + tmp = (u64)period_count << prescale;
> > + tmp *= NSEC_PER_SEC;
> > + real_state->period = DIV_ROUND_CLOSEST_ULL(tmp, rate);
> > +
> > + /*
> > + * if eventually the PWM output is inactive, either
> > + * duty cycle is 0 or status is disabled, need to
> > + * make sure the output pin is inactive.
> > + */
> > + if (!state->enabled)
> > + real_state->duty_cycle = 0;
> > + else
> > + real_state->duty_cycle = state->duty_cycle;
>
> You're maybe lying about the duty cycle here. Also it would be more
> consistent to calculate the value to be written into the CnV register that
> defines the duty cycle here.
>
> Regarding the period computation I'm happy with this function. Unless I miss
> something this function is idempotent (i.e. doing
>
> pwm_imx_tpm_round_state(chip, &p, some_state, &real_state1);
> pwm_imx_tpm_round_state(chip, &p, &real_state1, &real_state2);
>
> results in real_state1 == real_state2) given that
> clk_get_rate(tpm->clk) < NSEC_PER_SEC.
>

Sorry, I can NOT get your point, can you be more detail?

> > + real_state->polarity = state->polarity;
> > + real_state->enabled = state->enabled;
> > +
> > + return 0;
> > +}
> > +
>
> A comment here noting that pwm_imx_tpm_setup_period is supposed to be
> called with the mutex hold would be good here.

Fine.

>
> > +static void pwm_imx_tpm_setup_period(struct pwm_chip *chip,
> > + struct imx_tpm_pwm_param *p) {
> > + struct imx_tpm_pwm_chip *tpm = to_imx_tpm_pwm_chip(chip);
> > + u32 val, saved_cmod, cur_prescale;
> > +
> > + /* make sure counter is disabled for programming prescale */
>
> @Thierry: What is your thought here? IMHO this should only be allowed if all
> affected PWMs are off.

As we already make sure that ONLY when there is ONLY 1 user and the requested
period is different from the current period, then this function will be called, so there
is impossible that multiple PWMs are active and the period is requested to be changed.
Am I right?

>
> > + val = readl(tpm->base + PWM_IMX_TPM_SC);
> > + saved_cmod = FIELD_GET(PWM_IMX_TPM_SC_CMOD, val);
> > + cur_prescale = FIELD_GET(PWM_IMX_TPM_SC_PS, val);
> > + if (saved_cmod && cur_prescale != p->prescale) {
> > + val &= ~PWM_IMX_TPM_SC_CMOD;
> > + writel(val, tpm->base + PWM_IMX_TPM_SC);
> > + }
> > +
> > + /* set TPM counter prescale */
> > + val &= ~PWM_IMX_TPM_SC_PS;
> > + val |= FIELD_PREP(PWM_IMX_TPM_SC_PS, p->prescale);
> > + writel(val, tpm->base + PWM_IMX_TPM_SC);
> > +
> > + /* restore the clock mode if necessary */
> > + if (saved_cmod && cur_prescale != p->prescale) {
> > + val |= FIELD_PREP(PWM_IMX_TPM_SC_CMOD, saved_cmod);
> > + writel(val, tpm->base + PWM_IMX_TPM_SC);
> > + }
> > +
> > + /*
> > + * set period count:
> > + * according to RM, the MOD register is updated immediately
> > + * if CMOD[1:0] = 2b'00. if CMOD[1:0] != 2b'00, then MOD
> > + * register is updated according to the CPWMS bit, that is:
> > + *
> > + * if the selected mode is not CPWM then MOD register is
> > + * updated after MOD register was written and the TPM
> > + * counter changes from MOD to zero.
> > + *
> > + * if the selected mode is CPWM then MOD register is updated
> > + * after MOD register was written and the TPM counter changes
> > + * from MOD to (MOD â 1).
> > + */
> > + writel(p->mod, tpm->base + PWM_IMX_TPM_MOD); }
> > +
> > +static void pwm_imx_tpm_get_state(struct pwm_chip *chip,
> > + struct pwm_device *pwm,
> > + struct pwm_state *state)
> > +{
> > + struct imx_tpm_pwm_chip *tpm = to_imx_tpm_pwm_chip(chip);
> > + u32 rate, val, prescale;
> > + u64 tmp;
> > +
> > + /* get period */
> > + state->period = tpm->real_period;
> > +
> > + /* get duty cycle */
> > + rate = clk_get_rate(tpm->clk);
> > + val = readl(tpm->base + PWM_IMX_TPM_SC);
> > + prescale = FIELD_GET(PWM_IMX_TPM_SC_PS, val);
> > + tmp = readl(tpm->base + PWM_IMX_TPM_CnV(pwm->hwpwm));
> > + tmp = (tmp << prescale) * NSEC_PER_SEC;
> > + state->duty_cycle = DIV_ROUND_CLOSEST_ULL(tmp, rate);
> > +
> > + /* get polarity */
> > + val = readl(tpm->base + PWM_IMX_TPM_CnSC(pwm->hwpwm));
> > + if (FIELD_GET(PWM_IMX_TPM_CnSC_ELS, val) ==
> > + PWM_IMX_TPM_CnSC_ELS_POLARITY_INVERSED)
> > + state->polarity = PWM_POLARITY_INVERSED;
> > + else
> > + /*
> > + * Assume reserved values (2b00 and 2b11) to yield
> > + * normal polarity.
>
> Given that this driver writes PWM_IMX_TPM_CnSC_ELS = 2b00 in some
> situations assuming that this results in an constant inactive output, this
> should be recognized here. (Not entirely sure the output is inactive because
> of only PWM_IMX_TPM_CnSC_ELS = 2b00.)

Fine, then I can save the original requested polarity in each channel, and then return
the last requested polarity here, NOT read from hardware, since the polarity could be
different according to enable status.

>
> > + */
> > + state->polarity = PWM_POLARITY_NORMAL;
> > +
> > + /* get channel status */
> > + state->enabled = FIELD_GET(PWM_IMX_TPM_CnSC_ELS, val) ? true :
> > +false; }
> > +
> > +static void pwm_imx_tpm_apply_hw(struct pwm_chip *chip,
> > + struct pwm_device *pwm,
> > + struct pwm_state *state)
>
> pwm_imx_tpm_apply_hw is called with the mutex hold. Is this necessary?
> Please either call it without the mutex or annotate the function that the caller
> is supposed to hold it.

OK, will make sure call it without mutex hold.

>
> > +{
> > + struct imx_tpm_pwm_chip *tpm = to_imx_tpm_pwm_chip(chip);
> > + struct pwm_state c;
> > + u32 val, sc_val;
> > + u64 tmp;
> > +
> > + pwm_imx_tpm_get_state(chip, pwm, &c);
> > +
> > + if (state->duty_cycle != c.duty_cycle) {
> > + /* set duty counter */
> > + tmp = readl(tpm->base + PWM_IMX_TPM_MOD) &
> PWM_IMX_TPM_MOD_MOD;
> > + tmp *= state->duty_cycle;
> > + val = DIV_ROUND_CLOSEST_ULL(tmp, state->period);
> > + writel(val, tpm->base + PWM_IMX_TPM_CnV(pwm-
> >hwpwm));
>
> How does this affect a currently running PWM? Consider it runs at
> duty_cycle=500 + period=1000 and now should change to duty_cycle=700 +
> period=800. Can it happen that we see a or even several periods with
> duty_cycle=700 and period=1000?

The reference manual says, if counter is disabled, it will be updated immediately.
If counter is enabled, and for edge aligned PWM mode(EPWM), the register is updated
After written and TPM counter changes from MOD to zero, same as period count update,
HW will make sure the period finish..

If (CMOD[1:0] = 0:0) then CnV register is updated when CnV register is written.
If (CMOD[1:0] â 0:0), then CnV register is updated according to the selected mode, that
is:
â If the selected mode is output compare then CnV register is updated on the next TPM
counter increment (end of the prescaler counting) after CnV register was written.
Chapter 64 Low Power Timer/Pulse Width Modulation Module (TPM)
i.MX 7ULP Applications Processor Reference Manual 2.0, Rev. A, 12/2017
NXP Semiconductors Preliminary 2817
Confidential Proprietary
â If the selected mode is EPWM then CnV register is updated after CnV register was
written and the TPM counter changes from MOD to zero.
â If the selected mode is CPWM then CnV register is updated after CnV register was
written and the TPM counter changes from MOD to (MOD â 1).
64.5.14

>
> > + }
> > +
> > + if (state->enabled != c.enabled) {
>
> If the PWM was already on and is changed to another enabled state, you're
> ignoring the (maybe) new polarity here.
>
> > + /*
> > + * set polarity (for edge-aligned PWM modes)
> > + *
> > + * ELS[1:0] = 2b10 yields normal polarity behaviour,
> > + * ELS[1:0] = 2b01 yields inversed polarity.
> > + * The other values are reserved.
> > + *
> > + * polarity settings will enabled/disable output status
> > + * immediately, so if the channel is disabled, need to
> > + * make sure MSA/MSB/ELS are set to 0 which means channel
> > + * disabled.
> > + */
> > + val = readl(tpm->base + PWM_IMX_TPM_CnSC(pwm-
> >hwpwm));
> > + val &= ~(PWM_IMX_TPM_CnSC_ELS |
> PWM_IMX_TPM_CnSC_MSA |
> > + PWM_IMX_TPM_CnSC_MSB);
> > + sc_val = readl(tpm->base + PWM_IMX_TPM_SC);
> > + if (state->enabled) {
> > + val |= PWM_IMX_TPM_CnSC_MSB;
> > + val |= (state->polarity == PWM_POLARITY_NORMAL) ?
> > + PWM_IMX_TPM_CnSC_ELS_NORMAL :
> > + PWM_IMX_TPM_CnSC_ELS_INVERSED;
> > + if (++tpm->enable_count == 1) {
> > + /* start TPM counter */
> > + sc_val |=
> PWM_IMX_TPM_SC_CMOD_INC_EVERY_CLK;
> > + writel(sc_val, tpm->base +
> PWM_IMX_TPM_SC);
> > + }
> > + } else {
> > + if (--tpm->enable_count == 0) {
> > + /* stop TPM counter */
> > + sc_val &= ~PWM_IMX_TPM_SC_CMOD;
> > + writel(sc_val, tpm->base +
> PWM_IMX_TPM_SC);
> > + }
> > + }
> > + writel(val, tpm->base + PWM_IMX_TPM_CnSC(pwm-
> >hwpwm));
> > + }
> > +}
> > +
> > +static int pwm_imx_tpm_apply(struct pwm_chip *chip,
> > + struct pwm_device *pwm,
> > + struct pwm_state *state)
> > +{
> > + struct imx_tpm_pwm_chip *tpm = to_imx_tpm_pwm_chip(chip);
> > + struct imx_tpm_pwm_param param;
> > + struct pwm_state real_state;
> > + int ret;
> > +
> > + ret = pwm_imx_tpm_round_state(chip, &param, state, &real_state);
> > + if (ret)
> > + return -EINVAL;
> > +
> > + mutex_lock(&tpm->lock);
> > +
> > + /*
> > + * TPM counter is shared by multiple channels, so
> > + * prescale and period can NOT be modified when
> > + * there are multiple channels in use with different
> > + * period settings.
> > + */
> > + if (real_state.period != tpm->real_period) {
> > + if (tpm->user_count > 1) {
> > + ret = -EBUSY;
> > + goto exit;
> > + }
> > +
> > + pwm_imx_tpm_setup_period(chip, &param);
> > + tpm->real_period = real_state.period;
> > + }
> > +
> > + pwm_imx_tpm_apply_hw(chip, pwm, &real_state);
> > +
> > +exit:
> > + mutex_unlock(&tpm->lock);
>
> .apply is supposed to sleep until the newly configured state is active.
> This is missing here, right?

NOT quite understand, you meant .apply could be sleep if mutex is hold by
other thread?

BTW, can you have as more of your comments together as possible? That can
save some time of doing new patch, many thanks for your time and patience.

Anson.

>
> Best regards
> Uwe
>
> --
> Pengutronix e.K. | Uwe Kleine-KÃnig |
> Industrial Linux Solutions |
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