Re: [PATCH v5 1/7] pwm: pca9685: Switch to atomic API

[Clemens Gruber]

Hi Sven,

On Wed, Dec 16, 2020 at 10:58:07PM -0500, Sven Van Asbroeck wrote:
> Hi Clemens, this looks compact, simple and neat. I like it a lot !!

Thanks!

> 
> Few very minor nits below.
> 
> On Wed, Dec 16, 2020 at 7:53 AM Clemens Gruber
> <clemens.gruber@xxxxxxxxxxxx> wrote:
> >
> > The switch to the atomic API goes hand in hand with a few fixes to
> > previously experienced issues:
> > - The duty cycle is no longer lost after disable/enable (previously the
> >   OFF registers were cleared in disable and the user was required to
> >   call config to restore the duty cycle settings)
> > - If one sets a period resulting in the same prescale register value,
> >   the sleep and write to the register is now skipped
> >
> > Signed-off-by: Clemens Gruber <clemens.gruber@xxxxxxxxxxxx>
> > ---
> > Changes since v4:
> > - Patches split up
> > - Use a single set_duty function
> > - Improve readability / new macros
> > - Added a patch to restrict prescale changes to the first user
> >
> > Changes since v3:
> > - Refactoring: Extracted common functions
> > - Read prescale register value instead of caching it
> > - Return all zeros and disabled for "all LEDs" channel state
> > - Improved duty calculation / mapping to 0..4096
> >
> > Changes since v2:
> > - Always set default prescale value in probe
> > - Simplified probe code
> > - Inlined functions with one callsite
> >
> > Changes since v1:
> > - Fixed a logic error
> > - Impoved PM runtime handling and fixed !CONFIG_PM
> > - Write default prescale reg value if invalid in probe
> > - Reuse full_off/_on functions throughout driver
> > - Use cached prescale value whenever possible
> >
> >  drivers/pwm/pwm-pca9685.c | 253 +++++++++++++-------------------------
> >  1 file changed, 87 insertions(+), 166 deletions(-)
> >
> > diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> > index 4a55dc18656c..1b5b5fb93b43 100644
> > --- a/drivers/pwm/pwm-pca9685.c
> > +++ b/drivers/pwm/pwm-pca9685.c
> > @@ -51,7 +51,6 @@
> >  #define PCA9685_PRESCALE_MAX   0xFF    /* => min. frequency of 24 Hz */
> >
> >  #define PCA9685_COUNTER_RANGE  4096
> > -#define PCA9685_DEFAULT_PERIOD 5000000 /* Default period_ns = 1/200 Hz */
> >  #define PCA9685_OSC_CLOCK_MHZ  25      /* Internal oscillator with 25 MHz */
> >
> >  #define PCA9685_NUMREGS                0xFF
> > @@ -71,10 +70,14 @@
> >  #define LED_N_OFF_H(N) (PCA9685_LEDX_OFF_H + (4 * (N)))
> >  #define LED_N_OFF_L(N) (PCA9685_LEDX_OFF_L + (4 * (N)))
> >
> > +#define REG_ON_H(C)    ((C) >= PCA9685_MAXCHAN ? PCA9685_ALL_LED_ON_H : LED_N_ON_H((C)))
> > +#define REG_ON_L(C)    ((C) >= PCA9685_MAXCHAN ? PCA9685_ALL_LED_ON_L : LED_N_ON_L((C)))
> > +#define REG_OFF_H(C)   ((C) >= PCA9685_MAXCHAN ? PCA9685_ALL_LED_OFF_H : LED_N_OFF_H((C)))
> > +#define REG_OFF_L(C)   ((C) >= PCA9685_MAXCHAN ? PCA9685_ALL_LED_OFF_L : LED_N_OFF_L((C)))
> 
> Yes !!
> 
> > +
> >  struct pca9685 {
> >         struct pwm_chip chip;
> >         struct regmap *regmap;
> > -       int period_ns;
> >  #if IS_ENABLED(CONFIG_GPIOLIB)
> >         struct mutex lock;
> >         struct gpio_chip gpio;
> > @@ -87,6 +90,49 @@ static inline struct pca9685 *to_pca(struct pwm_chip *chip)
> >         return container_of(chip, struct pca9685, chip);
> >  }
> >
> > +static void pca9685_pwm_set_duty(struct pca9685 *pca, int channel, unsigned int duty)
> > +{
> 
> Add brief function documentation to clarify that 'duty' sets the duty cycle
> _ratio_ to 'duty/4096' on ? I.e.
> duty == 2048 => duty cycle ratio = 2048/4096 = 50%  on
> duty == 4096 => duty cycle ratio = 4096/4086 = 100% on etc

Will do.

> 
> > +       if (duty == 0) {
> > +               /* Set the full OFF bit, which has the highest precedence */
> > +               regmap_write(pca->regmap, REG_OFF_H(channel), LED_FULL);
> > +       } else if (duty >= PCA9685_COUNTER_RANGE) {
> > +               /* Set the full ON bit and clear the full OFF bit */
> > +               regmap_write(pca->regmap, REG_ON_H(channel), LED_FULL);
> > +               regmap_write(pca->regmap, REG_OFF_H(channel), 0);
> > +       } else {
> > +               /* Set OFF time (clears the full OFF bit) */
> > +               regmap_write(pca->regmap, REG_OFF_L(channel), duty & 0xff);
> > +               regmap_write(pca->regmap, REG_OFF_H(channel), (duty >> 8) & 0xf);
> > +               /* Clear the full ON bit */
> > +               regmap_write(pca->regmap, REG_ON_H(channel), 0);
> > +       }
> > +}
> > +
> > +static unsigned int pca9685_pwm_get_duty(struct pca9685 *pca, int channel)
> > +{
> > +       unsigned int off_h, val;
> > +
> > +       if (WARN_ON(channel >= PCA9685_MAXCHAN)) {
> > +               /* Hardware readout not supported for "all LEDs" channel */
> > +               return 0;
> > +       }
> > +
> > +       regmap_read(pca->regmap, LED_N_OFF_H(channel), &off_h);
> > +       if (off_h & LED_FULL) {
> 
> I believe this may trigger bots which are monitoring patches on LKML:
> if regmap_read() somehow fails, off_h will be used uninitialized.
>
> Prevent by initializing off_h and val?

I can initialize the values to 0 of course and check the file for other
places with missing initializations.

Or would it be better to check the return codes of regmap_read/write in
such cases? I'm not sure.

> 
> > +               /* Full OFF bit is set */
> > +               return 0;
> > +       }
> > +
> > +       regmap_read(pca->regmap, LED_N_ON_H(channel), &val);
> > +       if (val & LED_FULL) {
> > +               /* Full ON bit is set */
> > +               return PCA9685_COUNTER_RANGE;
> > +       }
> > +
> > +       regmap_read(pca->regmap, LED_N_OFF_L(channel), &val);
> > +       return ((off_h & 0xf) << 8) | (val & 0xff);
> > +}
> > +
> >  #if IS_ENABLED(CONFIG_GPIOLIB)
> >  static bool pca9685_pwm_test_and_set_inuse(struct pca9685 *pca, int pwm_idx)
> >  {
> > @@ -138,34 +184,23 @@ static int pca9685_pwm_gpio_request(struct gpio_chip *gpio, unsigned int offset)
> >  static int pca9685_pwm_gpio_get(struct gpio_chip *gpio, unsigned int offset)
> >  {
> >         struct pca9685 *pca = gpiochip_get_data(gpio);
> > -       struct pwm_device *pwm = &pca->chip.pwms[offset];
> > -       unsigned int value;
> >
> > -       regmap_read(pca->regmap, LED_N_ON_H(pwm->hwpwm), &value);
> > -
> > -       return value & LED_FULL;
> > +       return pca9685_pwm_get_duty(pca, offset) != 0;
> >  }
> >
> >  static void pca9685_pwm_gpio_set(struct gpio_chip *gpio, unsigned int offset,
> >                                  int value)
> >  {
> >         struct pca9685 *pca = gpiochip_get_data(gpio);
> > -       struct pwm_device *pwm = &pca->chip.pwms[offset];
> > -       unsigned int on = value ? LED_FULL : 0;
> > -
> > -       /* Clear both OFF registers */
> > -       regmap_write(pca->regmap, LED_N_OFF_L(pwm->hwpwm), 0);
> > -       regmap_write(pca->regmap, LED_N_OFF_H(pwm->hwpwm), 0);
> >
> > -       /* Set the full ON bit */
> > -       regmap_write(pca->regmap, LED_N_ON_H(pwm->hwpwm), on);
> > +       pca9685_pwm_set_duty(pca, offset, value ? PCA9685_COUNTER_RANGE : 0);
> >  }
> >
> >  static void pca9685_pwm_gpio_free(struct gpio_chip *gpio, unsigned int offset)
> >  {
> >         struct pca9685 *pca = gpiochip_get_data(gpio);
> >
> > -       pca9685_pwm_gpio_set(gpio, offset, 0);
> > +       pca9685_pwm_set_duty(pca, offset, 0);
> >         pm_runtime_put(pca->chip.dev);
> >         pca9685_pwm_clear_inuse(pca, offset);
> >  }
> > @@ -246,167 +281,56 @@ static void pca9685_set_sleep_mode(struct pca9685 *pca, bool enable)
> >         }
> >  }
> >
> > -static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> > -                             int duty_ns, int period_ns)
> > +static int pca9685_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> > +                            const struct pwm_state *state)
> >  {
> >         struct pca9685 *pca = to_pca(chip);
> > -       unsigned long long duty;
> > -       unsigned int reg;
> > -       int prescale;
> > -
> > -       if (period_ns != pca->period_ns) {
> > -               prescale = DIV_ROUND_CLOSEST(PCA9685_OSC_CLOCK_MHZ * period_ns,
> > -                                            PCA9685_COUNTER_RANGE * 1000) - 1;
> > -
> > -               if (prescale >= PCA9685_PRESCALE_MIN &&
> > -                       prescale <= PCA9685_PRESCALE_MAX) {
> > -                       /*
> > -                        * Putting the chip briefly into SLEEP mode
> > -                        * at this point won't interfere with the
> > -                        * pm_runtime framework, because the pm_runtime
> > -                        * state is guaranteed active here.
> > -                        */
> > -                       /* Put chip into sleep mode */
> > -                       pca9685_set_sleep_mode(pca, true);
> > -
> > -                       /* Change the chip-wide output frequency */
> > -                       regmap_write(pca->regmap, PCA9685_PRESCALE, prescale);
> > -
> > -                       /* Wake the chip up */
> > -                       pca9685_set_sleep_mode(pca, false);
> > -
> > -                       pca->period_ns = period_ns;
> > -               } else {
> > -                       dev_err(chip->dev,
> > -                               "prescaler not set: period out of bounds!\n");
> > -                       return -EINVAL;
> > -               }
> > -       }
> > +       unsigned long long duty, prescale;
> > +       unsigned int val = 0;
> >
> > -       if (duty_ns < 1) {
> > -               if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > -                       reg = PCA9685_ALL_LED_OFF_H;
> > -               else
> > -                       reg = LED_N_OFF_H(pwm->hwpwm);
> > +       if (state->polarity != PWM_POLARITY_NORMAL)
> > +               return -EOPNOTSUPP;
> >
> > -               regmap_write(pca->regmap, reg, LED_FULL);
> > -
> > -               return 0;
> > +       prescale = DIV_ROUND_CLOSEST_ULL(PCA9685_OSC_CLOCK_MHZ * state->period,
> > +                                        PCA9685_COUNTER_RANGE * 1000) - 1;
> > +       if (prescale < PCA9685_PRESCALE_MIN || prescale > PCA9685_PRESCALE_MAX) {
> > +               dev_err(chip->dev, "prescaler not set: period out of bounds!\n");
> 
> would "pwm not changed: period out of bounds" be a clearer error message here?

Yes, I think so. I'll change it in the next version.

> 
> > +               return -EINVAL;
> >         }
> >
> > -       if (duty_ns == period_ns) {
> > -               /* Clear both OFF registers */
> > -               if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > -                       reg = PCA9685_ALL_LED_OFF_L;
> > -               else
> > -                       reg = LED_N_OFF_L(pwm->hwpwm);
> > -
> > -               regmap_write(pca->regmap, reg, 0x0);
> > -
> > -               if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > -                       reg = PCA9685_ALL_LED_OFF_H;
> > -               else
> > -                       reg = LED_N_OFF_H(pwm->hwpwm);
> > -
> > -               regmap_write(pca->regmap, reg, 0x0);
> > -
> > -               /* Set the full ON bit */
> > -               if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > -                       reg = PCA9685_ALL_LED_ON_H;
> > -               else
> > -                       reg = LED_N_ON_H(pwm->hwpwm);
> > -
> > -               regmap_write(pca->regmap, reg, LED_FULL);
> > +       duty = PCA9685_COUNTER_RANGE * state->duty_cycle;
> > +       duty = DIV_ROUND_CLOSEST_ULL(duty, state->period);
> >
> > +       if (!state->enabled || duty < 1) {
> > +               pca9685_pwm_set_duty(pca, pwm->hwpwm, 0);
> > +               return 0;
> > +       } else if (duty == PCA9685_COUNTER_RANGE) {
> > +               pca9685_pwm_set_duty(pca, pwm->hwpwm, duty);
> >                 return 0;
> >         }
> >
> > -       duty = PCA9685_COUNTER_RANGE * (unsigned long long)duty_ns;
> > -       duty = DIV_ROUND_UP_ULL(duty, period_ns);
> > -
> > -       if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > -               reg = PCA9685_ALL_LED_OFF_L;
> > -       else
> > -               reg = LED_N_OFF_L(pwm->hwpwm);
> > -
> > -       regmap_write(pca->regmap, reg, (int)duty & 0xff);
> > -
> > -       if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > -               reg = PCA9685_ALL_LED_OFF_H;
> > -       else
> > -               reg = LED_N_OFF_H(pwm->hwpwm);
> > -
> > -       regmap_write(pca->regmap, reg, ((int)duty >> 8) & 0xf);
> > -
> > -       /* Clear the full ON bit, otherwise the set OFF time has no effect */
> > -       if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > -               reg = PCA9685_ALL_LED_ON_H;
> > -       else
> > -               reg = LED_N_ON_H(pwm->hwpwm);
> > -
> > -       regmap_write(pca->regmap, reg, 0);
> > -
> > -       return 0;
> > -}
> > -
> > -static int pca9685_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> > -{
> > -       struct pca9685 *pca = to_pca(chip);
> > -       unsigned int reg;
> > -
> > -       /*
> > -        * The PWM subsystem does not support a pre-delay.
> > -        * So, set the ON-timeout to 0
> > -        */
> > -       if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > -               reg = PCA9685_ALL_LED_ON_L;
> > -       else
> > -               reg = LED_N_ON_L(pwm->hwpwm);
> > -
> > -       regmap_write(pca->regmap, reg, 0);
> > -
> > -       if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > -               reg = PCA9685_ALL_LED_ON_H;
> > -       else
> > -               reg = LED_N_ON_H(pwm->hwpwm);
> > -
> > -       regmap_write(pca->regmap, reg, 0);
> > +       regmap_read(pca->regmap, PCA9685_PRESCALE, &val);
> > +       if (prescale != val) {
> > +               /*
> > +                * Putting the chip briefly into SLEEP mode
> > +                * at this point won't interfere with the
> > +                * pm_runtime framework, because the pm_runtime
> > +                * state is guaranteed active here.
> > +                */
> > +               /* Put chip into sleep mode */
> > +               pca9685_set_sleep_mode(pca, true);
> >
> > -       /*
> > -        * Clear the full-off bit.
> > -        * It has precedence over the others and must be off.
> > -        */
> > -       if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > -               reg = PCA9685_ALL_LED_OFF_H;
> > -       else
> > -               reg = LED_N_OFF_H(pwm->hwpwm);
> > +               /* Change the chip-wide output frequency */
> > +               regmap_write(pca->regmap, PCA9685_PRESCALE, (int)prescale);
> >
> > -       regmap_update_bits(pca->regmap, reg, LED_FULL, 0x0);
> > +               /* Wake the chip up */
> > +               pca9685_set_sleep_mode(pca, false);
> > +       }
> >
> > +       pca9685_pwm_set_duty(pca, pwm->hwpwm, duty);
> >         return 0;
> >  }
> >
> > -static void pca9685_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> > -{
> > -       struct pca9685 *pca = to_pca(chip);
> > -       unsigned int reg;
> > -
> > -       if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > -               reg = PCA9685_ALL_LED_OFF_H;
> > -       else
> > -               reg = LED_N_OFF_H(pwm->hwpwm);
> > -
> > -       regmap_write(pca->regmap, reg, LED_FULL);
> > -
> > -       /* Clear the LED_OFF counter. */
> > -       if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > -               reg = PCA9685_ALL_LED_OFF_L;
> > -       else
> > -               reg = LED_N_OFF_L(pwm->hwpwm);
> > -
> > -       regmap_write(pca->regmap, reg, 0x0);
> > -}
> > -
> >  static int pca9685_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
> >  {
> >         struct pca9685 *pca = to_pca(chip);
> > @@ -422,15 +346,13 @@ static void pca9685_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
> >  {
> >         struct pca9685 *pca = to_pca(chip);
> >
> > -       pca9685_pwm_disable(chip, pwm);
> > +       pca9685_pwm_set_duty(pca, pwm->hwpwm, 0);
> >         pm_runtime_put(chip->dev);
> >         pca9685_pwm_clear_inuse(pca, pwm->hwpwm);
> >  }
> >
> >  static const struct pwm_ops pca9685_pwm_ops = {
> > -       .enable = pca9685_pwm_enable,
> > -       .disable = pca9685_pwm_disable,
> > -       .config = pca9685_pwm_config,
> > +       .apply = pca9685_pwm_apply,
> >         .request = pca9685_pwm_request,
> >         .free = pca9685_pwm_free,
> >         .owner = THIS_MODULE,
> > @@ -461,7 +383,6 @@ static int pca9685_pwm_probe(struct i2c_client *client,
> >                         ret);
> >                 return ret;
> >         }
> > -       pca->period_ns = PCA9685_DEFAULT_PERIOD;
> >
> >         i2c_set_clientdata(client, pca);
> >
> > --
> > 2.29.2
> >

Thanks,
Clemens