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Date: Mon, 12 Apr 2021 19:11:58 +0200
From: Clemens Gruber <clemens.gruber@...ruber.com>
To: Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>
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
Hi,
On Mon, Apr 12, 2021 at 06:30:45PM +0200, Uwe Kleine-König wrote:
> 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 usage_power is false, LED_N_ON is guaranteed to be 0. It is reset to
0 in probe and never changed. Or did I miss something?
>
> > }
> >
> > #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.
No, I don't think so:
The third cell is optional with of_pwm_xlate_with_flags.
So previous DTs with pwm-cells = <2> will still work.
If you want to use the new flag for some PWMs you have to set pwm-cells
to <3> and PWM_USAGE_POWER (or 0) in the third field at the consumer.
This should not break backwards compatibility. Let me know if I missed
something.
Thanks for your review,
Clemens
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