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SubjectRe: [PATCH v2 1/1] gpio: mvebu: Add support for multiple PWM lines per GPIO chip
On Wed, Sep 12, 2018 at 8:01 PM Andrew Lunn <andrew@lunn.ch> wrote:
>
> > static int mvebu_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
> > {
> > struct mvebu_pwm *mvpwm = to_mvebu_pwm(chip);
> > struct mvebu_gpio_chip *mvchip = mvpwm->mvchip;
> > struct gpio_desc *desc;
> > + struct mvebu_pwm *counter;
> > unsigned long flags;
> > int ret = 0;
> >
> > spin_lock_irqsave(&mvpwm->lock, flags);
> >
> > - if (mvpwm->gpiod) {
> > - ret = -EBUSY;
> > - } else {
> > - desc = gpiochip_request_own_desc(&mvchip->chip,
> > - pwm->hwpwm, "mvebu-pwm");
> > - if (IS_ERR(desc)) {
> > - ret = PTR_ERR(desc);
> > + counter = mvpwm;
> > + if (counter->gpiod) {
> > + counter = mvebu_pwm_get_avail_counter();
> > + if (!counter) {
> > + ret = -EBUSY;
>
> I don't understand this bit of code. Please could you explain what is
> going on.
Check whether bank's default counter is already used. If it's used then
try to find and check other counter. If it also being used that mean both,
counter A and counter B, already assigned to some PWM device so
return EBUSY.

>
> > goto out;
> > }
> >
> > - ret = gpiod_direction_output(desc, 0);
> > - if (ret) {
> > - gpiochip_free_own_desc(desc);
> > - goto out;
> > - }
> > + pwm->chip_data = counter;
> > + }
> >
> > - mvpwm->gpiod = desc;
> > + desc = gpiochip_request_own_desc(&mvchip->chip,
> > + pwm->hwpwm, "mvebu-pwm");
> > + if (IS_ERR(desc)) {
> > + ret = PTR_ERR(desc);
> > + goto out;
> > }
> > +
> > + ret = gpiod_direction_output(desc, 0);
> > + if (ret) {
> > + gpiochip_free_own_desc(desc);
> > + goto out;
> > + }
> > +
> > + regmap_update_bits(mvchip->regs, GPIO_BLINK_CNT_SELECT_OFF +
> > + mvchip->offset, BIT(pwm->hwpwm),
> > + counter->id ? BIT(pwm->hwpwm) : 0);
> > + regmap_read(mvchip->regs, GPIO_BLINK_CNT_SELECT_OFF +
> > + mvchip->offset, &counter->blink_select);
> > +
> > + counter->gpiod = desc;
> > out:
> > spin_unlock_irqrestore(&mvpwm->lock, flags);
> > return ret;
> > @@ -632,6 +666,11 @@ static void mvebu_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
> > struct mvebu_pwm *mvpwm = to_mvebu_pwm(chip);
> > unsigned long flags;
> >
> > + if (pwm->chip_data) {
> > + mvpwm = (struct mvebu_pwm *) pwm->chip_data;
> > + pwm->chip_data = NULL;
> > + }
> > +
> > spin_lock_irqsave(&mvpwm->lock, flags);
> > gpiochip_free_own_desc(mvpwm->gpiod);
> > mvpwm->gpiod = NULL;
> > @@ -648,6 +687,9 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
> > unsigned long flags;
> > u32 u;
> >
> > + if (pwm->chip_data)
> > + mvpwm = (struct mvebu_pwm *) pwm->chip_data;
> > +
>
> You should not need a cast here, if chip_data is a void *.
>
> What is pwm->chip_data is a NULL? Don't you then use an uninitialized
> mvpwm?

mvpwm is declared and initialized as:
struct mvebu_pwm *mvpwm = to_mvebu_pwm(chip);
so it's not an uninitialized variable.
pwm->chip_data is set when the pwm use counter other then default.
pwm->chip_data take precedence over to_mvebu_pwm(chip).

After looked at other PWM driver, i think i should use pwm_set_chip_data()
and pwm_get_chip_data() instead of directly access pwm->chip_data.

Now i think it would be better if i use
struct mvebu_pwm *mvpwm = pwm_get_chip_data(pwm);
and pwm_set_chip_data() would be called during mvebu_pwm_probe() to
set the data to bank's default counter.

Aditya

> Andrew

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