Messages in this thread | | | Date | Thu, 19 Nov 2020 11:00:05 +0100 | From | Clemens Gruber <> | Subject | Re: [PATCH 1/3] pwm: pca9685: Switch to atomic API |
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Hi Sven,
thank you for your fast response and helpful feedback! I'll answer below.
On Wed, Nov 18, 2020 at 07:18:04PM -0500, Sven Van Asbroeck wrote: > 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@pqgruber.com> 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@pqgruber.com> > > --- > > 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?
Good point. I wanted .get_state to read out the actual HW state but the cached prescale register should always be identical to that, so it should be OK to use it here.
> > +{ > > + 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 are right, that's a mistake.
> 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?
Yes, sticking to the cached value is probably the way to go.
> 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 ||/&&.
Good idea!
> 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?
As long as it is overwritten with a correct setting when the PWM is used for the first time, it should be OK?
Thanks, Clemens
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