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Date: Mon, 23 Nov 2020 12:38:26 -0500
From: Sven Van Asbroeck <thesven73@...il.com>
To: Clemens Gruber <clemens.gruber@...ruber.com>
Cc: linux-pwm@...r.kernel.org,
Thierry Reding <thierry.reding@...il.com>,
Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>, Lee Jones <lee.jones@...aro.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Mika Westerberg <mika.westerberg@...ux.intel.com>,
David Jander <david@...tonic.nl>
Subject: Re: [PATCH v2 1/4] pwm: pca9685: Switch to atomic API
Hi Clemens, some cool changes, thank you !! Constructive feedback below.
On Mon, Nov 23, 2020 at 11:36 AM Clemens Gruber
<clemens.gruber@...ruber.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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