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Date: Mon, 12 Apr 2021 18:30:45 +0200
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To: Clemens Gruber <clemens.gruber@...ruber.com>
Cc: linux-pwm@...r.kernel.org,
Thierry Reding <thierry.reding@...il.com>,
Sven Van Asbroeck <TheSven73@...il.com>,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 6/8] pwm: pca9685: Support new PWM_USAGE_POWER flag
On Mon, Apr 12, 2021 at 03:27:43PM +0200, Clemens Gruber wrote:
> If PWM_USAGE_POWER is set on a PWM, the pca9685 driver will phase shift
> the individual channels relative to their channel number. This improves
> EMI because the enabled channels no longer turn on at the same time,
> while still maintaining the configured duty cycle / power output.
>
> Signed-off-by: Clemens Gruber <clemens.gruber@...ruber.com>
> ---
> drivers/pwm/pwm-pca9685.c | 63 ++++++++++++++++++++++++++++++---------
> 1 file changed, 49 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> index 7f97965033e7..410b93b115dc 100644
> --- a/drivers/pwm/pwm-pca9685.c
> +++ b/drivers/pwm/pwm-pca9685.c
> @@ -93,46 +93,76 @@ static inline struct pca9685 *to_pca(struct pwm_chip *chip)
> /* Helper function to set the duty cycle ratio to duty/4096 (e.g. duty=2048 -> 50%) */
> static void pca9685_pwm_set_duty(struct pca9685 *pca, int channel, unsigned int duty)
> {
> + struct pwm_device *pwm = &pca->chip.pwms[channel];
> + unsigned int on, off;
> +
> if (duty == 0) {
> /* Set the full OFF bit, which has the highest precedence */
> regmap_write(pca->regmap, REG_OFF_H(channel), LED_FULL);
> + return;
> } else if (duty >= PCA9685_COUNTER_RANGE) {
> /* Set the full ON bit and clear the full OFF bit */
> regmap_write(pca->regmap, REG_ON_H(channel), LED_FULL);
> regmap_write(pca->regmap, REG_OFF_H(channel), 0);
> - } else {
> - /* Set OFF time (clears the full OFF bit) */
> - regmap_write(pca->regmap, REG_OFF_L(channel), duty & 0xff);
> - regmap_write(pca->regmap, REG_OFF_H(channel), (duty >> 8) & 0xf);
> - /* Clear the full ON bit */
> - regmap_write(pca->regmap, REG_ON_H(channel), 0);
> + return;
> }
> +
> +
> + if (pwm->args.usage_power && channel < PCA9685_MAXCHAN) {
> + /*
> + * If PWM_USAGE_POWER is set on a PWM, the pca9685
> + * driver will phase shift the individual channels
> + * relative to their channel number.
> + * This improves EMI because the enabled channels no
> + * longer turn on at the same time, while still
> + * maintaining the configured duty cycle / power output.
> + */
> + on = channel * PCA9685_COUNTER_RANGE / PCA9685_MAXCHAN;
> + } else
> + on = 0;
> +
> + off = (on + duty) % PCA9685_COUNTER_RANGE;
> +
> + /* Set ON time (clears full ON bit) */
> + regmap_write(pca->regmap, REG_ON_L(channel), on & 0xff);
> + regmap_write(pca->regmap, REG_ON_H(channel), (on >> 8) & 0xf);
> + /* Set OFF time (clears full OFF bit) */
> + regmap_write(pca->regmap, REG_OFF_L(channel), off & 0xff);
> + regmap_write(pca->regmap, REG_OFF_H(channel), (off >> 8) & 0xf);
> }
>
> static unsigned int pca9685_pwm_get_duty(struct pca9685 *pca, int channel)
> {
> - unsigned int off_h = 0, val = 0;
> + struct pwm_device *pwm = &pca->chip.pwms[channel];
> + unsigned int off = 0, on = 0, val = 0;
>
> if (WARN_ON(channel >= PCA9685_MAXCHAN)) {
> /* HW does not support reading state of "all LEDs" channel */
> return 0;
> }
>
> - regmap_read(pca->regmap, LED_N_OFF_H(channel), &off_h);
> - if (off_h & LED_FULL) {
> + regmap_read(pca->regmap, LED_N_OFF_H(channel), &off);
> + if (off & LED_FULL) {
> /* Full OFF bit is set */
> return 0;
> }
>
> - regmap_read(pca->regmap, LED_N_ON_H(channel), &val);
> - if (val & LED_FULL) {
> + regmap_read(pca->regmap, LED_N_ON_H(channel), &on);
> + if (on & LED_FULL) {
> /* Full ON bit is set */
> return PCA9685_COUNTER_RANGE;
> }
>
> - val = 0;
> regmap_read(pca->regmap, LED_N_OFF_L(channel), &val);
> - return ((off_h & 0xf) << 8) | (val & 0xff);
> + off = ((off & 0xf) << 8) | (val & 0xff);
> + if (!pwm->args.usage_power)
> + return off;
> +
> + /* Read ON register to calculate duty cycle of staggered output */
> + val = 0;
> + regmap_read(pca->regmap, LED_N_ON_L(channel), &val);
> + on = ((on & 0xf) << 8) | (val & 0xff);
> + return (off - on) & (PCA9685_COUNTER_RANGE - 1);
If LED_N_ON is != 0 but usage_power is false, the returned state is
bogus.
> }
>
> #if IS_ENABLED(CONFIG_GPIOLIB)
> @@ -439,9 +469,11 @@ static int pca9685_pwm_probe(struct i2c_client *client,
> reg &= ~(MODE1_ALLCALL | MODE1_SUB1 | MODE1_SUB2 | MODE1_SUB3);
> regmap_write(pca->regmap, PCA9685_MODE1, reg);
>
> - /* Reset OFF registers to POR default */
> + /* Reset OFF/ON registers to POR default */
> regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_L, LED_FULL);
> regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, LED_FULL);
> + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0);
> + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_H, 0);
>
> pca->chip.ops = &pca9685_pwm_ops;
> /* Add an extra channel for ALL_LED */
> @@ -450,6 +482,9 @@ static int pca9685_pwm_probe(struct i2c_client *client,
> pca->chip.dev = &client->dev;
> pca->chip.base = -1;
>
> + pca->chip.of_xlate = of_pwm_xlate_with_flags;
> + pca->chip.of_pwm_n_cells = 3;
> +
Huh, you're incompatibly changing the device tree binding here.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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