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SubjectRe: [PATCH v6] gpio: pca953x: Add Maxim MAX7313 PWM support
Hello Uwe,

Thanks for the review!

Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote on Fri, 3 Jul
2020 16:53:13 +0200:

> Hello Miquel,
>
> On Sun, May 03, 2020 at 12:54:53PM +0200, Miquel Raynal wrote:
> > +static u8 max7313_pwm_get_intensity(struct pca953x_chip *pca_chip,
> > + unsigned int idx)
> > +{
> > + struct device *dev = &pca_chip->client->dev;
> > + unsigned int reg, shift, val, output;
> > + u8 intensity;
> > + bool phase;
> > + int ret;
> > +
> > + /* Retrieve the intensity */
> > + reg = MAX7313_INTENSITY + (idx / PWM_PER_REG);
> > + shift = (idx % PWM_PER_REG) ? PWM_BITS_PER_REG : 0;
>
> I would find
>
> shift = (idx % PWM_PER_REG) * PWM_BITS_PER_REG
>
> more natural here as your formula only works for PWM_PER_REG = 2.

Understood.

>
> > + mutex_lock(&pca_chip->i2c_lock);
> > + ret = regmap_read(pca_chip->regmap, reg, &val);
> > + mutex_unlock(&pca_chip->i2c_lock);
> > + if (ret < 0) {
> > + dev_err(dev, "Cannot retrieve PWM intensity (%d)\n", ret);
>
> Please use %pe for error codes.

Fine, fixed at three relevant locations.

>
> > + return 0;
> > + }
> > +
> > + val >>= shift;
> > + val &= PWM_INTENSITY_MASK;
> > +
> > + /* Retrieve the phase */
> > + reg = pca953x_recalc_addr(pca_chip, pca_chip->regs->output, idx, 0, 0);
> > +
> > + mutex_lock(&pca_chip->i2c_lock);
> > + ret = regmap_read(pca_chip->regmap, reg, &output);
> > + mutex_unlock(&pca_chip->i2c_lock);
> > + if (ret < 0) {
> > + dev_err(dev, "Cannot retrieve PWM phase (%d)\n", ret);
> > + return 0;
> > + }
> > +
> > + phase = output & BIT(idx % BANK_SZ);
>
> Would it make sense to cache the phase value to reduce register access
> and locking here?

I suppose it could be done and would certainly reduce register access a
little bit but it means refactoring quite some code and as I'm not near
the board to actually test these changes right now I fear to do
something wrong. Instead, I'd prefer not to touch that part, and let
users that would need this enhancement do it themselves if you don't
mind.

>
> > [...]
> > +static int max7313_pwm_apply(struct pwm_chip *chip,
> > + struct pwm_device *pwm,
> > + const struct pwm_state *state)
> > +{
> > + struct max7313_pwm *max_pwm = to_max7313_pwm(chip);
> > + struct pca953x_chip *pca_chip = to_pca953x(max_pwm);
> > + unsigned int intensity, active;
> > + int ret = 0;
> > +
> > + if (!state->enabled ||
> > + state->period < PWM_PERIOD_NS ||
> > + state->polarity != PWM_POLARITY_NORMAL)
> > + return -EINVAL;
>
> You could simulate state->enabled = false using duty_cycle = 0.

Absolutely!

>
> > + /* Convert the duty-cycle to be in the [0;16] range */
> > + intensity = max7313_pwm_duty_to_intensity(state->duty_cycle);
>
> This might return a value > 16 if state->duty_cycle > PWM_PERIOD_NS.
> I suggest to do
>
> duty_cycle = min(state->duty_cycle, PWM_PERIOD_NS);
>
> and use that value instead of state->duty_cycle.

Done.

>
> > + /*
> > + * The hardware is supposedly glitch-free when changing the intensity,
> > + * unless we need to flip the blink phase to reach an extremity or the
> > + * other of the spectrum (0/16 from phase 1, 16/16 from phase 0).
>
> s/other of/other end of/. I don't understand the difference between
> extremity and "other end of the spectrum".

Fixed.

>
> > + */
> > + return max7313_pwm_set_state(pca_chip, pwm, intensity);
> > +}
> > +
> > +static void max7313_pwm_get_state(struct pwm_chip *chip,
> > + struct pwm_device *pwm,
> > + struct pwm_state *state)
> > +{
> > + struct max7313_pwm *max_pwm = to_max7313_pwm(chip);
> > + struct pca953x_chip *pca_chip = to_pca953x(max_pwm);
> > + u8 intensity;
> > +
> > + state->enabled = true;
> > + state->period = PWM_PERIOD_NS;
> > + state->polarity = PWM_POLARITY_NORMAL;
> > +
> > + intensity = max7313_pwm_get_intensity(pca_chip, pwm->hwpwm);
> > + state->duty_cycle = max7313_pwm_intensity_to_duty(intensity);
>
> Please round up the division in max7313_pwm_intensity_to_duty().

I understand the use case, done as well.

I will respin a compile tested version rebased on top of current master
(which includes Linus-W GPIO-5.9-1 merge request).

Thanks,
Miquèl

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