Messages in this thread | | | From | Sven Van Asbroeck <> | Date | Mon, 23 Nov 2020 12:38:26 -0500 | Subject | Re: [PATCH v2 1/4] pwm: pca9685: Switch to atomic API |
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Hi Clemens, some cool changes, thank you !! Constructive feedback below.
On Mon, Nov 23, 2020 at 11:36 AM Clemens Gruber <clemens.gruber@pqgruber.com> wrote: > > 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 | 295 ++++++++++++++++++++------------------ > 1 file changed, 159 insertions(+), 136 deletions(-) > > diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c > index 4a55dc18656c..47a69ee7951f 100644 > --- a/drivers/pwm/pwm-pca9685.c > +++ b/drivers/pwm/pwm-pca9685.c > @@ -47,11 +47,11 @@ > #define PCA9685_ALL_LED_OFF_H 0xFD > #define PCA9685_PRESCALE 0xFE > > +#define PCA9685_PRESCALE_DEF 0x1E /* => default frequency of ~200 Hz */ > #define PCA9685_PRESCALE_MIN 0x03 /* => max. frequency of 1526 Hz */ > #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 +74,7 @@ > struct pca9685 { > struct pwm_chip chip; > struct regmap *regmap; > - int period_ns; > + int prescale; > #if IS_ENABLED(CONFIG_GPIOLIB) > struct mutex lock; > struct gpio_chip gpio; > @@ -87,6 +87,61 @@ static inline struct pca9685 *to_pca(struct pwm_chip *chip) > return container_of(chip, struct pca9685, chip); > } > > +static inline bool is_prescale_valid(int prescale) > +{ > + return prescale >= PCA9685_PRESCALE_MIN && > + prescale <= PCA9685_PRESCALE_MAX; > +} > + > +static void pca9685_pwm_full_off(struct pca9685 *pca, int index) > +{ > + 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 (index >= PCA9685_MAXCHAN) > + reg = PCA9685_ALL_LED_OFF_H; > + else > + reg = LED_N_OFF_H(index); > + > + regmap_write(pca->regmap, reg, LED_FULL); > +} > + > +static void pca9685_pwm_full_on(struct pca9685 *pca, int index) > +{ > + 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 (index >= PCA9685_MAXCHAN) > + reg = PCA9685_ALL_LED_OFF_L; > + else > + reg = LED_N_OFF_L(index); > + > + regmap_write(pca->regmap, reg, 0); > + > + if (index >= PCA9685_MAXCHAN) > + reg = PCA9685_ALL_LED_OFF_H; > + else > + reg = LED_N_OFF_H(index); > + > + regmap_write(pca->regmap, reg, 0); > + > + if (index >= PCA9685_MAXCHAN) > + reg = PCA9685_ALL_LED_ON_H; > + else > + reg = LED_N_ON_H(index); > + > + regmap_write(pca->regmap, reg, LED_FULL); > +} > + > + > #if IS_ENABLED(CONFIG_GPIOLIB) > static bool pca9685_pwm_test_and_set_inuse(struct pca9685 *pca, int pwm_idx) > { > @@ -141,31 +196,27 @@ static int pca9685_pwm_gpio_get(struct gpio_chip *gpio, unsigned int offset) > struct pwm_device *pwm = &pca->chip.pwms[offset]; > unsigned int value; > > - regmap_read(pca->regmap, LED_N_ON_H(pwm->hwpwm), &value); > + regmap_read(pca->regmap, LED_N_OFF_H(pwm->hwpwm), &value); > > - return value & LED_FULL; > + return !(value & LED_FULL); > } > > 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); > + if (value) > + pca9685_pwm_full_on(pca, offset); > + else > + pca9685_pwm_full_off(pca, offset); > } > > 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_full_off(pca, offset); > pm_runtime_put(pca->chip.dev); > pca9685_pwm_clear_inuse(pca, offset); > } > @@ -246,36 +297,75 @@ 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_set_prescale(struct pca9685 *pca, int prescale) > +{ > + /* 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->prescale = prescale; > +}
Refactoring this code as a "general purpose" function is very dangerous, IMHO. This code jumps over the runtime_pm's head to overwrite the sleep mode, and should be used only in very specific cases / places in the code, where this is guaranteed safe.
Leaving this as a function might give future contributors the idea that they can just call this anywhere.
Suggestion: for better maintainability, leave this code in pwm_apply, close to the comment that explains why it's safe to execute.
> + > +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; > + > + /* Calculate (chip-wide) period from cached prescale value */ > + state->period = (PCA9685_COUNTER_RANGE * 1000 / PCA9685_OSC_CLOCK_MHZ) * > + (pca->prescale + 1); > + > + /* 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; > > - if (prescale >= PCA9685_PRESCALE_MIN && > - prescale <= PCA9685_PRESCALE_MAX) { > + prescale = DIV_ROUND_CLOSEST_ULL(PCA9685_OSC_CLOCK_MHZ * state->period, > + PCA9685_COUNTER_RANGE * 1000) - 1; > + if (prescale != pca->prescale) { > + if (is_prescale_valid(prescale)) { > /* > * 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; > + pca9685_set_prescale(pca, (int)prescale); > } else { > dev_err(chip->dev, > "prescaler not set: period out of bounds!\n"); > @@ -283,46 +373,18 @@ 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(pca, pwm->hwpwm); > 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(pca, pwm->hwpwm); > 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 +411,6 @@ 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 +426,14 @@ 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(pca, pwm->hwpwm); > 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 +451,7 @@ 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 +464,17 @@ 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 (is_prescale_valid(prescale)) > + pca->prescale = prescale; > + else { > + /* If invalid, use HW default prescale value */ > + pca9685_set_prescale(pca, PCA9685_PRESCALE_DEF); > + } > + > regmap_read(pca->regmap, PCA9685_MODE2, ®); > > if (device_property_read_bool(&client->dev, "invert")) > @@ -505,14 +515,20 @@ static int pca9685_pwm_probe(struct i2c_client *client, > return ret; > } > > - /* The chip comes out of power-up in the active state */ > - pm_runtime_set_active(&client->dev); > - /* > - * Enable will put the chip into suspend, which is what we > - * want as all outputs are disabled at this point > - */ > + /* Set runtime PM status according to chip sleep state */ > + if (reg & MODE1_SLEEP) > + pm_runtime_set_suspended(&client->dev); > + else > + pm_runtime_set_active(&client->dev); > + > + /* If active, enable puts chip into suspend until first use */ > pm_runtime_enable(&client->dev); > > + if (!IS_ENABLED(CONFIG_PM)) { > + /* Wake the chip up on non-PM environments */ > + pca9685_set_sleep_mode(pca, false); > + } > +
IMHO this is quite complex probe code, with all kinds of subtle corner cases.
Normally in a probe() function, we want code that: - is simple && easy to understand - puts the chip in a known state (no corner cases due to leftover state) - if this takes a one or two extra reads/writes that's fine - clarity is more important than efficiency in a probe() function, which executes maybe once a day?
I feel that the pca9685 is a chip with lots of little "gotchas". Best to keep things as simple as possible?
Suggestion:
probe() { ...
/* Always initialize with default prescale, but chip must be * in sleep mode while changing prescaler. */ pca9685_set_sleep_mode(pca, true); pca->prescale = PCA9685_PRESCALE_DEF; regmap_write(pca->regmap, PCA9685_PRESCALE, pca->prescale); pm_runtime_set_suspended(&client->dev); pm_runtime_enable(&client->dev);
if (!IS_ENABLED(CONFIG_PM)) { /* Wake the chip up on non-PM environments */ pca9685_set_sleep_mode(pca, false); }
return 0; }
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