RE: [PATCH V2 2/5] pwm: Add i.MX TPM PWM driver support

From: Anson Huang
Date: Thu Mar 14 2019 - 05:49:57 EST

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Hi, Uwe

Best Regards!
Anson Huang

> -----Original Message-----
> From: Uwe Kleine-KÃnig [mailto:u.kleine-koenig@xxxxxxxxxxxxxx]
> Sent: 2019å3æ14æ 17:17
> 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 V2 2/5] pwm: Add i.MX TPM PWM driver support
>
> On Wed, Mar 13, 2019 at 07:31:16AM +0000, Anson Huang wrote:
> > i.MX7ULP has TPM(Low Power Timer/Pulse Width Modulation Module)
> > inside, add TPM PWM driver support.
> >
> > Signed-off-by: Anson Huang <Anson.Huang@xxxxxxx>
> > ---
> > Changes since V1:
> > - improve coding style, function name's prefix;
> > - improve Kconfig's help info;
> > - use .apply instead for .enable/.disable/.config etc. to simply the
> code;
> > - improve clock operation, make clock enabled during probe phase
> and ONLY disabled
> > when suspend, as register read/write need to sync with clock,
> keeping it enabled
> > makes the register read/write simple;
> > - improve prescale calculation;
> > - add error message print during probe for ioremap and clk get;
> > ---
> > drivers/pwm/Kconfig | 10 ++
> > drivers/pwm/Makefile | 1 +
> > drivers/pwm/pwm-imx-tpm.c | 332
> > ++++++++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 343 insertions(+)
> > create mode 100644 drivers/pwm/pwm-imx-tpm.c
> >
> > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig index
> > a8f47df..c1cbb43 100644
> > --- a/drivers/pwm/Kconfig
> > +++ b/drivers/pwm/Kconfig
> > @@ -201,6 +201,16 @@ config PWM_IMX
> > To compile this driver as a module, choose M here: the module
> > will be called pwm-imx.
> >
> > +config PWM_IMX_TPM
> > + tristate "i.MX TPM PWM support"
> > + depends on ARCH_MXC
>
> Can you please make this
>
> depends on ARCH_MXC || COMPILE_TEST
> depends on HAVE_CLK && HAS_IOMEM
>

OK.

> > + 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
> > 9c676a0..64e036c 100644
> > --- a/drivers/pwm/Makefile
> > +++ b/drivers/pwm/Makefile
> > @@ -18,6 +18,7 @@ obj-$(CONFIG_PWM_FSL_FTM) += pwm-fsl-ftm.o
> > obj-$(CONFIG_PWM_HIBVT) += pwm-hibvt.o
> > obj-$(CONFIG_PWM_IMG) += pwm-img.o
> > obj-$(CONFIG_PWM_IMX) += pwm-imx.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..8c1a1ba
> > --- /dev/null
> > +++ b/drivers/pwm/pwm-imx-tpm.c
> > @@ -0,0 +1,332 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright 2018-2019 NXP.
> > + */
> > +
> > +#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>
> > +#include <linux/spinlock.h>
> > +
> > +#define TPM_GLOBAL 0x8
> > +#define TPM_SC 0x10
> > +#define TPM_CNT 0x14
> > +#define TPM_MOD 0x18
> > +#define TPM_C0SC 0x20
> > +#define TPM_C0V 0x24
>
> PWM_IMX_TPM_COV etc. please

I thought with IMX_ as prefix should be enough, but OK, I can change it to PWM_IMX_

>
> > +
> > +#define TPM_SC_CMOD_SHIFT 3
> > +#define TPM_SC_CMOD_MASK (0x3 << TPM_SC_CMOD_SHIFT)
>
> If you use the macros that are documented in <linux/bitops.h> you don't
> need these MASK and SHIFT stuff.
>

Already use GENMASK(h,l) in V3.

> > +#define TPM_SC_CPWMS BIT(5)
> > +
> > +#define TPM_CnSC_CHF BIT(7)
> > +#define TPM_CnSC_MSnB BIT(5)
> > +#define TPM_CnSC_MSnA BIT(4)
> > +#define TPM_CnSC_ELSnB BIT(3)
> > +#define TPM_CnSC_ELSnA BIT(2)
> > +
> > +#define TPM_SC_PS_MASK 0x7
> > +#define TPM_MOD_MOD_MASK 0xffff
> > +
> > +#define TPM_COUNT_MAX 0xffff
> > +
> > +#define TPM_CHn_ADDR_OFFSET 0x8
> > +#define TPM_DEFAULT_PWM_CHANNEL_NUM 2
>
> Is this better called "..._MAX_..." instead of "..._DEFAULT_..."? This is used as
> array size below and when reading
>
> u32 chn_config[TPM_DEFAULT_PWM_CHANNEL_NUM];
>
> I wonder if the actual number of PWMs can be bigger than the default.

OK, will use _MAX_ for this, I double checked i.MX7ULP RM, looks like some TPM
modules have ONLY 2 channel, but some have 6 channels, so I will change it to 6.

>
> > +struct imx_tpm_pwm_chip {
> > + struct pwm_chip chip;
> > + struct clk *clk;
> > + void __iomem *base;
> > + spinlock_t lock;
> > + u32 chn_config[TPM_DEFAULT_PWM_CHANNEL_NUM];
> > + bool chn_status[TPM_DEFAULT_PWM_CHANNEL_NUM];
> > +};
> > +
> > +#define to_imx_tpm_pwm_chip(_chip) container_of(_chip, struct
> imx_tpm_pwm_chip, chip)
> > +
> > +static void imx_tpm_pwm_config_counter(struct pwm_chip *chip, u32
> > +period) {
> > + struct imx_tpm_pwm_chip *tpm = to_imx_tpm_pwm_chip(chip);
> > + unsigned int period_cnt;
> > + u32 val, div;
> > + u64 tmp;
> > +
> > + tmp = clk_get_rate(tpm->clk);
> > + tmp *= period;
> > + val = DIV_ROUND_CLOSEST_ULL(tmp, NSEC_PER_SEC);
> > + if (val < TPM_COUNT_MAX)
> > + div = 0;
> > + else
> > + div = ilog2(roundup_pow_of_two(val / TPM_COUNT_MAX));
>
> Are you sure you have to divide by TPM_COUNT_MAX and not by
> (TPM_COUNT_MAX + 1)?

Ah, yes, when counter reach the TPM_COUNT_MAX, next value will from 0 in
counting up mode we used, will use TPM_COUNT_MAX + 1.

>
> > + if (div > TPM_SC_PS_MASK) {
> > + dev_err(chip->dev,
> > + "failed to find valid prescale value!\n");
> > + return;
>
> I think you should handle this failure and make imx_tpm_pwm_apply() fail.

OK.

>
> > + }
> > + /* set TPM counter prescale */
> > + val = readl(tpm->base + TPM_SC);
> > + val &= ~TPM_SC_PS_MASK;
> > + val |= div;
> > + writel(val, tpm->base + TPM_SC);
>
> According to the documentation PS can only be written if the counter is
> disabled, I think this isn't ensured here.

OK, I will make sure counter is disabled before writing it.

>
> > + /* set period counter */
> > + do_div(tmp, NSEC_PER_SEC);
> > + period_cnt = DIV_ROUND_CLOSEST_ULL(tmp, 1 << div);
> > + writel(period_cnt & TPM_MOD_MOD_MASK, tpm->base +
> TPM_MOD);
>
> If there is already a value pending in the MOD register, another write to it is
> ignored. A comment, why this cannot happen, would be appropriate. (Note,
> I'm not sure this cannot happen.)

Currently, we ONLY initialize the MOD register ONCE, so it does NOT have this case,
if we make the MOD register can be updated, then maybe I can read back the register
value after writing the new value, to make sure the register value is what we want to write?

>
> > +}
> > +
> > +static void imx_tpm_pwm_config(struct pwm_chip *chip,
> > + struct pwm_device *pwm,
> > + struct pwm_state *state)
> > +{
> > + struct imx_tpm_pwm_chip *tpm = to_imx_tpm_pwm_chip(chip);
> > + static bool tpm_cnt_initialized;
> > + unsigned int duty_cnt;
> > + u32 val;
> > + u64 tmp;
> > +
> > + /*
> > + * TPM counter is shared by multi channels, let's make it to be
> > + * ONLY first channel can config TPM counter's precale and period
> > + * count.
> > + */
> > + if (!tpm_cnt_initialized) {
> > + imx_tpm_pwm_config_counter(chip, state->period);
> > + tpm_cnt_initialized = true;
> > + }
>
> So the period can only be configured once. That is not as good as it could be.
> You should allow a change whenever there is exactly one PWM in use.

OK, maybe I can add check for other channels' statue here, and allow the period
update if ONLY 1 channel is enabled.

>
> > + /* set duty counter */
> > + tmp = readl(tpm->base + TPM_MOD) & TPM_MOD_MOD_MASK;
> > + tmp *= state->duty_cycle;
> > + duty_cnt = DIV_ROUND_CLOSEST_ULL(tmp, state->period);
>
> Uah, you use state->period here even though for the 2nd PWM the Divider
> might not be setup appropriately.

I think that is 1 limitation here, the dts should make sure the period used for
different channels are same or at least they can share same divider, otherwise,
what if multiple channels can NOT find a divider good for every channel? How to
deal with this case?

>
> > [...]
> > +static int imx_tpm_pwm_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 pwm_state curstate;
> > + unsigned long flags;
> > +
> > + imx_tpm_pwm_get_state(chip, pwm, &curstate);
> > +
> > + spin_lock_irqsave(&tpm->lock, flags);
> > +
> > + if (state->period != curstate.period ||
> > + state->duty_cycle != curstate.duty_cycle ||
> > + state->polarity != curstate.polarity)
> > + imx_tpm_pwm_config(chip, pwm, state);
> > +
> > + if (state->enabled != curstate.enabled)
> > + imx_tpm_pwm_enable(chip, pwm, state->enabled);
>
> This is wrong. This sequence:
>
> pwm_apply_state(pwm, { .duty_cycle = 0, .period = 10000, .enabled =
> true });
> pwm_apply_state(pwm, { .duty_cycle = 10000, .period =
> 10000, .enabled = false });
>
> must keep the output pin low which isn't guaranteed here.

So you mean for every .apply operation, the channel MUST be disabled first, then config
it, then enable it?

>
> > +
> > + spin_unlock_irqrestore(&tpm->lock, flags);
> > +
> > + return 0;
> > +}
>
> I didn't look in depth through the complete driver yet, but there is IIRC still
> some feedback on v1 that wasn't addressed in v2 (because v2 was sent
> before the last feedback). So I will look in more depth in v3 (assuming it
> comes late enough address the concerns from this mail).

Thanks, will address all comments before sending out V4.

Anson.

>
> Best regards
> Uwe
>
> --
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In reply to: Uwe Kleine-König: "Re: [PATCH V2 2/5] pwm: Add i.MX TPM PWM driver support"
Next in thread: Uwe Kleine-König: "Re: [PATCH V2 2/5] pwm: Add i.MX TPM PWM driver support"
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