Re: [PATCH v2 2/5] pwm: Add support for the MSTAR MSC313 PWM

[Romain Perier <romain.perier@gmail.com>]

Hi,


Le mar. 27 sept. 2022 à 18:33, Uwe Kleine-König
<u.kleine-koenig@pengutronix.de> a écrit :
>
> Hello Romain, hello Daniel,
>
> adding Mark Brown to Cc: for the regmap stuff.
>
> On Wed, Sep 07, 2022 at 03:12:38PM +0200, Romain Perier wrote:
> > From: Daniel Palmer <daniel@0x0f.com>
> >
> > This adds support for the PWM block on the Mstar MSC313e SoCs and newer.
> >
> > Signed-off-by: Daniel Palmer <daniel@0x0f.com>
> > Co-developed-by: Romain Perier <romain.perier@gmail.com>
> > Signed-off-by: Romain Perier <romain.perier@gmail.com>
> > ---
> >  MAINTAINERS               |   1 +
> >  drivers/pwm/Kconfig       |   9 ++
> >  drivers/pwm/Makefile      |   1 +
> >  drivers/pwm/pwm-msc313e.c | 269 ++++++++++++++++++++++++++++++++++++++
> >  4 files changed, 280 insertions(+)
> >  create mode 100644 drivers/pwm/pwm-msc313e.c
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 9d7f64dc0efe..c3b39b09097c 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -2439,6 +2439,7 @@ F:      arch/arm/mach-mstar/
> >  F:   drivers/clk/mstar/
> >  F:   drivers/clocksource/timer-msc313e.c
> >  F:   drivers/gpio/gpio-msc313.c
> > +F:   drivers/pwm/pwm-msc313e.c
> >  F:   drivers/rtc/rtc-msc313.c
> >  F:   drivers/watchdog/msc313e_wdt.c
> >  F:   include/dt-bindings/clock/mstar-*
> > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> > index 60d13a949bc5..8049fd03a821 100644
> > --- a/drivers/pwm/Kconfig
> > +++ b/drivers/pwm/Kconfig
> > @@ -372,6 +372,15 @@ config PWM_MESON
> >         To compile this driver as a module, choose M here: the module
> >         will be called pwm-meson.
> >
> > +config PWM_MSC313E
> > +     tristate "MStar MSC313e PWM support"
> > +     depends on ARCH_MSTARV7 || COMPILE_TEST
> > +     help
> > +       Generic PWM framework driver for MSTAR MSC313e.
> > +
> > +       To compile this driver as a module, choose M here: the module
> > +       will be called pwm-msc313e.
> > +
> >  config PWM_MTK_DISP
> >       tristate "MediaTek display PWM driver"
> >       depends on ARCH_MEDIATEK || COMPILE_TEST
> > diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> > index 7bf1a29f02b8..bc285c054f2a 100644
> > --- a/drivers/pwm/Makefile
> > +++ b/drivers/pwm/Makefile
> > @@ -62,4 +62,5 @@ obj-$(CONFIG_PWM_TWL)               += pwm-twl.o
> >  obj-$(CONFIG_PWM_TWL_LED)    += pwm-twl-led.o
> >  obj-$(CONFIG_PWM_VISCONTI)   += pwm-visconti.o
> >  obj-$(CONFIG_PWM_VT8500)     += pwm-vt8500.o
> > +obj-$(CONFIG_PWM_MSC313E)    += pwm-msc313e.o
> >  obj-$(CONFIG_PWM_XILINX)     += pwm-xilinx.o
> > diff --git a/drivers/pwm/pwm-msc313e.c b/drivers/pwm/pwm-msc313e.c
> > new file mode 100644
> > index 000000000000..a71f39ba66c3
> > --- /dev/null
> > +++ b/drivers/pwm/pwm-msc313e.c
> > @@ -0,0 +1,269 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2021 Daniel Palmer <daniel@thingy.jp>
> > + * Copyright (C) 2022 Romain Perier <romain.perier@gmail.com>
> > + */
> > +
> > +#include <linux/clk.h>
> > +#include <linux/of_device.h>
> > +#include <linux/pwm.h>
> > +#include <linux/regmap.h>
> > +
> > +#define DRIVER_NAME "msc313e-pwm"
> > +
> > +#define CHANNEL_OFFSET       0x80
> > +#define REG_DUTY     0x8
> > +#define REG_PERIOD   0x10
> > +#define REG_DIV              0x18
> > +#define REG_CTRL     0x1c
> > +#define REG_SWRST    0x1fc
> > +
> > +struct msc313e_pwm_channel {
> > +     struct regmap_field *clkdiv;
> > +     struct regmap_field *polarity;
> > +     struct regmap_field *dutyl;
> > +     struct regmap_field *dutyh;
> > +     struct regmap_field *periodl;
> > +     struct regmap_field *periodh;
> > +     struct regmap_field *swrst;
> > +};
> > +
> > +struct msc313e_pwm {
> > +     struct regmap *regmap;
> > +     struct pwm_chip pwmchip;
> > +     struct clk *clk;
> > +     struct msc313e_pwm_channel channels[];
> > +};
> > +
> > +struct msc313e_pwm_info {
> > +     unsigned int channels;
> > +};
> > +
> > +#define to_msc313e_pwm(ptr) container_of(ptr, struct msc313e_pwm, pwmchip)
> > +
> > +static const struct regmap_config msc313e_pwm_regmap_config = {
> > +     .reg_bits = 16,
> > +     .val_bits = 16,
> > +     .reg_stride = 4,
> > +};
> > +
> > +static const struct msc313e_pwm_info msc313e_data = {
> > +     .channels = 8,
> > +};
> > +
> > +static const struct msc313e_pwm_info ssd20xd_data = {
> > +     .channels = 4,
> > +};
> > +
> > +static void msc313e_pwm_writecounter(struct regmap_field *low, struct regmap_field *high, u32 value)
> > +{
> > +     /* The bus that connects the CPU to the peripheral registers splits 32 bit registers into
>
> Please fix the comment style to use /* on a line for itself. Also for
> comments staying below 80 chars per line is appreciated.

even if check-patch.pl --strict passed ? ^^

>
> > +      * two 16bit registers placed 4 bytes apart. It's the hardware design they used. The counter
> > +      * we are about to write has this contrainst.
>
> s/contrainst/contraint/
>
> I wonder if that could be abstracted by regmap?!

I had the same thought, not from what I have read/found, but perhaps
the regmap maintainer has an opinion.

>
> > +      */
> > +     regmap_field_write(low, value & 0xffff);
> > +     regmap_field_write(high, value >> 16);
> > +}
> > +
> > +static void msc313e_pwm_readcounter(struct regmap_field *low, struct regmap_field *high, u32 *value)
> > +{
> > +     unsigned int val = 0;
> > +
> > +     regmap_field_read(low, &val);
> > +     *value = val;
> > +     regmap_field_read(high, &val);
> > +     *value = (val << 16) | *value;
> > +}
> > +
> > +static int msc313e_pwm_config(struct pwm_chip *chip, struct pwm_device *device,
> > +                           int duty_ns, int period_ns)
> > +{
> > +     struct msc313e_pwm *pwm = to_msc313e_pwm(chip);
> > +     unsigned long long nspertick = DIV_ROUND_DOWN_ULL(NSEC_PER_SEC, clk_get_rate(pwm->clk));
> > +     struct msc313e_pwm_channel *channel = &pwm->channels[device->hwpwm];
> > +     unsigned long long div = 1;
> > +
> > +     /* Fit the period into the period register by prescaling the clk */
> > +     while (DIV_ROUND_DOWN_ULL(period_ns, nspertick) > 0x3ffff) {
>
> dividing by the result of a division looses precision. Also rounding
> down both divisions looks wrong.

Such cases are not supposed to be covered by PWM_DEBUG ? (because
everything passed with PWM_DEBUG)


>
> > +             div++;
> > +             if (div > (0xffff + 1)) {
> > +                     /* Force clk div to the maximum allowed value */
> > +                     div = 0xffff;
> > +                     break;
> > +             }
> > +             nspertick = DIV_ROUND_DOWN_ULL(nspertick, div);
> > +     }
> > +
> > +     regmap_field_write(channel->clkdiv, div - 1);
> > +     msc313e_pwm_writecounter(channel->dutyl, channel->dutyh,
> > +                              DIV_ROUND_DOWN_ULL(duty_ns, nspertick));
> > +     msc313e_pwm_writecounter(channel->periodl, channel->periodh,
> > +                              DIV_ROUND_DOWN_ULL(period_ns, nspertick));
> > +     return 0;
> > +};
> > +
> > +static int msc313e_pwm_set_polarity(struct pwm_chip *chip, struct pwm_device *device,
> > +                                 enum pwm_polarity polarity)
> > +{
> > +     struct msc313e_pwm *pwm = to_msc313e_pwm(chip);
> > +     struct msc313e_pwm_channel *channel = &pwm->channels[device->hwpwm];
> > +     unsigned int pol = 0;
> > +
> > +     if (polarity == PWM_POLARITY_INVERSED)
> > +             pol = 1;
> > +     regmap_field_update_bits(channel->polarity, 1, pol);
> > +
> > +     return 0;
> > +}
> > +
> > +static int msc313e_pwm_enable(struct pwm_chip *chip, struct pwm_device *device)
> > +{
> > +     struct msc313e_pwm *pwm = to_msc313e_pwm(chip);
> > +     struct msc313e_pwm_channel *channel = &pwm->channels[device->hwpwm];
> > +     int ret;
> > +
> > +     ret = clk_prepare_enable(pwm->clk);
> > +     if (ret)
> > +             return ret;
> > +     return regmap_field_write(channel->swrst, 0);
> > +}
> > +
> > +static int msc313e_pwm_disable(struct pwm_chip *chip, struct pwm_device *device)
> > +{
> > +     struct msc313e_pwm *pwm = to_msc313e_pwm(chip);
> > +     struct msc313e_pwm_channel *channel = &pwm->channels[device->hwpwm];
> > +     int ret;
> > +
> > +     ret = regmap_field_write(channel->swrst, 1);
> > +     clk_disable_unprepare(pwm->clk);
> > +     return ret;
> > +}
> > +
> > +static int msc313e_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> > +                      const struct pwm_state *state)
> > +{
> > +     int ret;
> > +
> > +     if (state->enabled) {
> > +             if (!pwm->state.enabled) {
> > +                     ret = msc313e_pwm_enable(chip, pwm);
> > +                     if (ret)
> > +                             return ret;
> > +             }
> > +             msc313e_pwm_set_polarity(chip, pwm, state->polarity);
> > +             msc313e_pwm_config(chip, pwm, state->duty_cycle, state->period);
>
> Does the output emit a previous setting after msc313e_pwm_enable()? If
> so, please do the enable at the end.
>
> Does calling msc313e_pwm_set_polarity() and msc313e_pwm_config() have an
> immediate effect? Or is the currently running period completed?
>
> > +     } else if (pwm->state.enabled) {
> > +             ret = msc313e_pwm_disable(chip, pwm);
>
> How does the output behave on disable? Typical options are:
>
>  - freezes where ever it currently is
>  - goes to the inactive level

I let Daniel answer these questions.


>
> Does it complete the currently running period? Please answer these in a
> "Limitations:" section similar to e.g. pwm-sl28cpld.c and pwm-iqs620a.
>
> > +     }
> > +     return 0;
> > +}
> > +
> > +static void msc313e_get_state(struct pwm_chip *chip, struct pwm_device *device,
>
> Please s/device/pwm/ to match the naming used in other drivers.
>
> > +                           struct pwm_state *state)
> > +{
> > +     struct msc313e_pwm *pwm = to_msc313e_pwm(chip);
> > +     struct msc313e_pwm_channel *channel = &pwm->channels[device->hwpwm];
> > +     unsigned long long nspertick = DIV_ROUND_DOWN_ULL(NSEC_PER_SEC, clk_get_rate(pwm->clk));
> > +     unsigned int val = 0;
> > +
> > +     regmap_field_read(channel->polarity, &val);
> > +     state->polarity = val ? PWM_POLARITY_INVERSED : PWM_POLARITY_NORMAL;
> > +
> > +     regmap_field_read(channel->swrst, &val);
> > +     state->enabled = val == 0 ? true : false;
> > +
> > +     msc313e_pwm_readcounter(channel->dutyl, channel->dutyh, &val);
> > +     state->duty_cycle = val * nspertick;
>
> Please do the division at the end. Consider val = 333335 and
> clk_get_rate() returning 666666667.
>
> Then the exact duty cycle would be 500002.49974999874 but you would
> calculate nspertick = 1 and so duty_cycle = 333335.
>
> Also you need to round up. Did you test your driver with PWM_DEBUG
> enabled?

Take a look at my cover letter, yeah I have tested everything with
PWM_DEBUG, everything passed ^^

The idea is that .get_state should return 500003 here to have
> apply ∘ get_state idempotent. As apply is supposed to round down to the
> next available setting, get_state has to round up.
>
> > +     msc313e_pwm_readcounter(channel->periodl, channel->periodh, &val);
> > +     state->period = val * nspertick;
> > +}
> > +
> > +static const struct pwm_ops msc313e_pwm_ops = {
> > +     .apply = msc313e_apply,
> > +     .get_state = msc313e_get_state,
> > +     .owner = THIS_MODULE
> > +};
> > +
> > +static int msc313e_pwm_probe(struct platform_device *pdev)
> > +{
> > +     const struct msc313e_pwm_info *match_data;
> > +     struct device *dev = &pdev->dev;
> > +     struct msc313e_pwm *pwm;
> > +     __iomem void *base;
> > +     int i;
> > +
> > +     match_data = of_device_get_match_data(dev);
> > +     if (!match_data)
> > +             return -EINVAL;
> > +
> > +     base = devm_platform_ioremap_resource(pdev, 0);
> > +     if (IS_ERR(base))
> > +             return PTR_ERR(base);
> > +
> > +     pwm = devm_kzalloc(dev, struct_size(pwm, channels, match_data->channels), GFP_KERNEL);
>
> Please don't use "pwm" as a name for your driver data variable. That
> name is reserved for struct pwm_device pointers. Something like "ddata"
> would be fine, but there is a wide variety in pwm driver land to choose
> from.
>
> > +     if (!pwm)
> > +             return -ENOMEM;
> > +
> > +     pwm->clk = devm_clk_get(dev, NULL);
> > +     if (IS_ERR(pwm->clk))
> > +             return dev_err_probe(dev, PTR_ERR(pwm->clk), "Cannot get clk\n");
> > +
> > +     pwm->regmap = devm_regmap_init_mmio(dev, base, &msc313e_pwm_regmap_config);
> > +     if (IS_ERR(pwm->regmap))
> > +             return dev_err_probe(dev, PTR_ERR(pwm->regmap), "Cannot get regmap\n");
> > +
> > +     for (i = 0; i < match_data->channels; i++) {
> > +             unsigned int offset = CHANNEL_OFFSET * i;
> > +             struct reg_field div_clkdiv_field = REG_FIELD(offset + REG_DIV, 0, 7);
> > +             struct reg_field ctrl_polarity_field = REG_FIELD(offset + REG_CTRL, 4, 4);
> > +             struct reg_field dutyl_field = REG_FIELD(offset + REG_DUTY, 0, 15);
> > +             struct reg_field dutyh_field = REG_FIELD(offset + REG_DUTY + 4, 0, 2);
> > +             struct reg_field periodl_field = REG_FIELD(offset + REG_PERIOD, 0, 15);
> > +             struct reg_field periodh_field = REG_FIELD(offset + REG_PERIOD + 4, 0, 2);
> > +             struct reg_field swrst_field = REG_FIELD(REG_SWRST, i, i);
> > +
> > +             pwm->channels[i].clkdiv = devm_regmap_field_alloc(dev, pwm->regmap,
> > +                                                               div_clkdiv_field);
> > +             pwm->channels[i].polarity = devm_regmap_field_alloc(dev, pwm->regmap,
> > +                                                                 ctrl_polarity_field);
> > +             pwm->channels[i].dutyl = devm_regmap_field_alloc(dev, pwm->regmap, dutyl_field);
> > +             pwm->channels[i].dutyh = devm_regmap_field_alloc(dev, pwm->regmap, dutyh_field);
> > +             pwm->channels[i].periodl = devm_regmap_field_alloc(dev, pwm->regmap, periodl_field);
> > +             pwm->channels[i].periodh = devm_regmap_field_alloc(dev, pwm->regmap, periodh_field);
> > +             pwm->channels[i].swrst = devm_regmap_field_alloc(dev, pwm->regmap, swrst_field);
> > +
> > +             /* Channels are enabled on boot, disable it until the pwm subsystem re-enable it
> > +              * explicitly
>
> You're supposed to keep the PWM running. (Consider a bootloader setting
> up a splash screen. You're probably killing the backlight here.) Note
> you need improved clk handling to do that right.
>
> > +              */
> > +             regmap_field_write(pwm->channels[i].swrst, 1);
> > +     }
> > +
> > +     pwm->pwmchip.dev = dev;
> > +     pwm->pwmchip.ops = &msc313e_pwm_ops;
> > +     pwm->pwmchip.npwm = match_data->channels;
> > +
> > +     platform_set_drvdata(pdev, pwm);
>
> This is unused, please drop.
>
> > +     return devm_pwmchip_add(dev, &pwm->pwmchip);
> > +}
> > +
> > +static const struct of_device_id msc313e_pwm_dt_ids[] = {
> > +     { .compatible = "mstar,msc313e-pwm", .data = &msc313e_data },
> > +     { .compatible = "mstar,ssd20xd-pwm", .data = &ssd20xd_data },
> > +     {},
> > +};
> > +MODULE_DEVICE_TABLE(of, msc313e_pwm_dt_ids);
> > +
> > +static struct platform_driver msc313e_pwm_driver = {
> > +     .probe = msc313e_pwm_probe,
> > +     .driver = {
> > +             .name = DRIVER_NAME,
> > +             .of_match_table = msc313e_pwm_dt_ids,
> > +     },
> > +};
> > +module_platform_driver(msc313e_pwm_driver);
> > +
> > +MODULE_LICENSE("GPL v2");
> > +MODULE_DESCRIPTION("Mstar MSC313e PWM driver");
> > +MODULE_AUTHOR("Daniel Palmer <daniel@thingy.jp>");
>
> That address doesn't match the author of this patch. Is this on purpose?
>
> Best regards
> Uwe


Regards,
Romain