Re: [PATCH 1/3] pwm: pca9685: Switch to atomic API

From: Sven Van Asbroeck
Date: Wed Nov 18 2020 - 19:18:20 EST

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In reply to: Clemens Gruber: "[PATCH 3/3] pwm: pca9685: Support staggered output ON times"
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Hi Clemens, thank you so much for this contribution.
I no longer have access to this chip, so I cannot test
the changes.

Some friendly/constructive feedback below.

On Wed, Nov 18, 2020 at 12:44 PM Clemens Gruber
<clemens.gruber@xxxxxxxxxxxx> wrote:
>
> This 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)
> - The prescale register is now read out. If one sets a period resulting
> in the same prescale register value, the sleep and write to the
> register is skipped
>
> The hardware readout may return slightly different values than those
> that were set in apply due to the limited range of possible prescale and
> counter register values. If one channel is reconfigured with new duty
> cycle and period, the others will keep the same relative duty cycle to
> period ratio as they had before, even though the per-chip / global
> frequency changed. (The PCA9685 has only one prescaler!)
>
> Note that although the datasheet mentions 200 Hz as default frequency
> when using the internal 25 MHz oscillator, the calculated period from
> the default prescaler register setting of 30 is 5079040ns.
>
> Signed-off-by: Clemens Gruber <clemens.gruber@xxxxxxxxxxxx>
> ---
> drivers/pwm/pwm-pca9685.c | 233 ++++++++++++++++++++------------------
> 1 file changed, 124 insertions(+), 109 deletions(-)
>
> diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> index 4a55dc18656c..20f1314e6754 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
> @@ -74,7 +73,7 @@
> struct pca9685 {
> struct pwm_chip chip;
> struct regmap *regmap;
> - int period_ns;
> + int prescale;

You've decided to cache the prescale register...

> #if IS_ENABLED(CONFIG_GPIOLIB)
> struct mutex lock;
> struct gpio_chip gpio;
> @@ -246,18 +245,117 @@ 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 void pca9685_pwm_full_off(struct pwm_chip *chip,
> + struct pwm_device *pwm)
> +{
> + struct pca9685 *pca = to_pca(chip);
> + int reg;
> +
> + /*
> + * Set the full OFF bit to cause the PWM channel to be always off.
> + * The full OFF bit has precedence over the other register values.
> + */
> +
> + 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);
> +}
> +
> +static void pca9685_pwm_full_on(struct pwm_chip *chip,
> + struct pwm_device *pwm)
> +{
> + struct pca9685 *pca = to_pca(chip);
> + int reg;
> +
> + /*
> + * Clear the OFF registers (including the full OFF bit) and set
> + * the full ON bit to cause the PWM channel to be always on.
> + */
> +
> + 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);
> +
> + 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);
> +}
> +
> +static int pca9685_pwm_read_global_period(struct pca9685 *pca)

but in this function, you don't seem to use the cached prescale
value, but read it out again instead?

> +{
> + unsigned int prescale = 0;
> +
> + regmap_read(pca->regmap, PCA9685_PRESCALE, &prescale);
> +
> + if (prescale < PCA9685_PRESCALE_MIN || prescale > PCA9685_PRESCALE_MAX)
> + return 0;
> +
> + return (PCA9685_COUNTER_RANGE * 1000 / PCA9685_OSC_CLOCK_MHZ) *
> + (prescale + 1);
> +}
> +
> +static void pca9685_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> + struct pwm_state *state)
> +{
> + struct pca9685 *pca = to_pca(chip);
> + unsigned int val, duty;
> + int reg;
> +
> + /* Read out (chip-wide) period */
> + state->period = pca9685_pwm_read_global_period(pca);
> +
> + /* The (per-channel) polarity is fixed */
> + state->polarity = PWM_POLARITY_NORMAL;
> +
> + /* Read out current duty cycle and enabled state */
> + reg = pwm->hwpwm >= PCA9685_MAXCHAN ? PCA9685_ALL_LED_OFF_H :
> + LED_N_OFF_H(pwm->hwpwm);
> + regmap_read(pca->regmap, reg, &val);
> + duty = (val & 0xf) << 8;
> +
> + state->enabled = !(val & LED_FULL);
> +
> + reg = pwm->hwpwm >= PCA9685_MAXCHAN ? PCA9685_ALL_LED_OFF_L :
> + LED_N_OFF_L(pwm->hwpwm);
> + regmap_read(pca->regmap, reg, &val);
> + duty |= (val & 0xff);
> +
> + if (duty < PCA9685_COUNTER_RANGE) {
> + duty *= state->period;
> + state->duty_cycle = duty / (PCA9685_COUNTER_RANGE - 1);
> + } else
> + state->duty_cycle = 0;
> +}
> +
> +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 long long duty, prescale;
> 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 (state->polarity != PWM_POLARITY_NORMAL)
> + return -EOPNOTSUPP;
>
> + prescale = DIV_ROUND_CLOSEST_ULL(PCA9685_OSC_CLOCK_MHZ * state->period,
> + PCA9685_COUNTER_RANGE * 1000) - 1;
> + if (prescale != pca->prescale) {

Use of cached prescale here, all good.

> if (prescale >= PCA9685_PRESCALE_MIN &&
> prescale <= PCA9685_PRESCALE_MAX) {
> /*
> @@ -270,12 +368,13 @@ static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> pca9685_set_sleep_mode(pca, true);
>
> /* Change the chip-wide output frequency */
> - regmap_write(pca->regmap, PCA9685_PRESCALE, prescale);
> + regmap_write(pca->regmap, PCA9685_PRESCALE,
> + (int)prescale);
>
> /* Wake the chip up */
> pca9685_set_sleep_mode(pca, false);
>
> - pca->period_ns = period_ns;
> + pca->prescale = (int)prescale;
> } else {
> dev_err(chip->dev,
> "prescaler not set: period out of bounds!\n");
> @@ -283,46 +382,18 @@ static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> }
> }
>
> - if (duty_ns < 1) {
> - 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);
> -
> + if (!state->enabled || state->duty_cycle < 1) {
> + pca9685_pwm_full_off(chip, pwm);
> return 0;
> }
>
> - 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);
> -
> + if (state->duty_cycle == state->period) {
> + pca9685_pwm_full_on(chip, pwm);
> return 0;
> }
>
> - duty = PCA9685_COUNTER_RANGE * (unsigned long long)duty_ns;
> - duty = DIV_ROUND_UP_ULL(duty, period_ns);
> + duty = (PCA9685_COUNTER_RANGE - 1) * state->duty_cycle;
> + duty = DIV_ROUND_UP_ULL(duty, state->period);
>
> if (pwm->hwpwm >= PCA9685_MAXCHAN)
> reg = PCA9685_ALL_LED_OFF_L;
> @@ -349,64 +420,6 @@ static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> 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);
> -
> - /*
> - * 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);
> -
> - regmap_update_bits(pca->regmap, reg, LED_FULL, 0x0);
> -
> - 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 +435,14 @@ 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_full_off(chip, pwm);
> 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,
> + .get_state = pca9685_pwm_get_state,
> + .apply = pca9685_pwm_apply,
> .request = pca9685_pwm_request,
> .free = pca9685_pwm_free,
> .owner = THIS_MODULE,
> @@ -448,7 +460,7 @@ static int pca9685_pwm_probe(struct i2c_client *client,
> {
> struct pca9685 *pca;
> unsigned int reg;
> - int ret;
> + int prescale = 0, ret;
>
> pca = devm_kzalloc(&client->dev, sizeof(*pca), GFP_KERNEL);
> if (!pca)
> @@ -461,10 +473,13 @@ static int pca9685_pwm_probe(struct i2c_client *client,
> ret);
> return ret;
> }
> - pca->period_ns = PCA9685_DEFAULT_PERIOD;
>
> i2c_set_clientdata(client, pca);
>
> + regmap_read(pca->regmap, PCA9685_PRESCALE, &prescale);
> + if (prescale < PCA9685_PRESCALE_MIN || prescale > PCA9685_PRESCALE_MAX)
> + pca->prescale = prescale;

I'm not sure this will cache the prescale value correctly,
the logic seems inverted.

You appear to mix cached and uncached uses of prescale,
is there a need for this? If not, perhaps pick one and use
it consistently?

Perhaps you can define a is_prescale_valid() helper,
which is easier to read.
And it can be easily negated:
if (!is_prescale_valid(prescale))
without getting confused between </>. <=/>=, and ||/&&.

Also, if the prescale register contains an invalid value
during probe(), e.g. 0x00 or 0x01, would it make sense
to explicitly overwrite it with a valid setting?

> +
> regmap_read(pca->regmap, PCA9685_MODE2, &reg);
>
> if (device_property_read_bool(&client->dev, "invert"))
> --
> 2.29.2
>

Next message: Abhishek Kumar: "Re: [PATCH v3] ath10k: Fix the parsing error in service available event"
Previous message: David E. Box: "[PATCH 1/2] PCI: Add save/restore of Precision Time Measurement capability"
In reply to: Clemens Gruber: "[PATCH 3/3] pwm: pca9685: Support staggered output ON times"
Next in thread: Clemens Gruber: "Re: [PATCH 1/3] pwm: pca9685: Switch to atomic API"
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