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Thu, 17 Dec 2020 12:51:06 -0500 Received: from workstation.tuxnet (213-47-165-233.cable.dynamic.surfer.at [213.47.165.233]) by mail.pqgruber.com (Postfix) with ESMTPSA id 558C5C727E0; Thu, 17 Dec 2020 18:50:23 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pqgruber.com; s=mail; t=1608227423; bh=5yv6lGeSgyryVCNTl8aoCTVLcb95oe95IW/ZaqfogQw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=R3LLK/FB1wRB0FrDR4XOoYTk4Z2wq1g5a9f6hYSj4dxKcpxZ5+gKj3kJIp6wWAmqe 55FqK4NYQuDNhqLVZtTpZImcG83LMYyAVha2mNMjgvtUTqjqn/LFqHIqaCjLDnaN9D keGIykFcA0Kx5UNm/ZWvDKIl8d1ihFtMGCjJ6w5Q= Date: Thu, 17 Dec 2020 18:50:22 +0100 From: Clemens Gruber To: Sven Van Asbroeck Cc: linux-pwm@vger.kernel.org, Thierry Reding , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Lee Jones , Linux Kernel Mailing List , Mika Westerberg , David Jander Subject: Re: [PATCH v5 5/7] pwm: pca9685: Support staggered output ON times Message-ID: References: <20201215212228.185517-1-clemens.gruber@pqgruber.com> <20201215212228.185517-5-clemens.gruber@pqgruber.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 16, 2020 at 11:02:57PM -0500, Sven Van Asbroeck wrote: > Hi Clemens, see below. > > On Wed, Dec 16, 2020 at 7:53 AM Clemens Gruber > wrote: > > > > The PCA9685 supports staggered LED output ON times to minimize current > > surges and reduce EMI. > > When this new option is enabled, the ON times of each channel are > > delayed by channel number x counter range / 16, which avoids asserting > > all enabled outputs at the same counter value while still maintaining > > the configured duty cycle of each output. > > > > Signed-off-by: Clemens Gruber > > --- > > drivers/pwm/pwm-pca9685.c | 62 +++++++++++++++++++++++++++++++-------- > > 1 file changed, 50 insertions(+), 12 deletions(-) > > > > diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c > > index 38aadaf50996..ff916980de49 100644 > > --- a/drivers/pwm/pwm-pca9685.c > > +++ b/drivers/pwm/pwm-pca9685.c > > @@ -79,6 +79,7 @@ > > struct pca9685 { > > struct pwm_chip chip; > > struct regmap *regmap; > > + bool staggered_outputs; > > #if IS_ENABLED(CONFIG_GPIOLIB) > > struct mutex lock; > > struct gpio_chip gpio; > > @@ -93,45 +94,79 @@ static inline struct pca9685 *to_pca(struct pwm_chip *chip) > > > > static void pca9685_pwm_set_duty(struct pca9685 *pca, int channel, unsigned int duty) > > { > > + 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 (pca->staggered_outputs) { > > + if (channel < PCA9685_MAXCHAN) { > > + /* > > + * To reduce EMI, the ON times of each channel are > > + * spread out evenly within the counter range, while > > + * still maintaining the configured duty cycle > > + */ > > + on = channel * PCA9685_COUNTER_RANGE / PCA9685_MAXCHAN; > > + off = (on + duty) % PCA9685_COUNTER_RANGE; > > + regmap_write(pca->regmap, REG_ON_L(channel), on & 0xff); > > + regmap_write(pca->regmap, REG_ON_H(channel), (on >> 8) & 0xf); > > + regmap_write(pca->regmap, REG_OFF_L(channel), off & 0xff); > > + regmap_write(pca->regmap, REG_OFF_H(channel), (off >> 8) & 0xf); > > + return; > > + } > > + /* No staggering possible if "all LEDs" channel is used */ > > + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0); > > } > > + /* 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); > > } > > I find the set_duty() function quite hard to follow. > Can we simplify this by eliminating the !staggered_outputs special case? > E.g. always calculate and write 'on' and 'off'. > But if !staggered_outputs => on = 0 and off = duty. > > Yes this adds one extra/unnecessary register write in the !staggered case, > but simplicity/maintainability >>> efficiency here. And this "issue" will > disappear when we switch on regmap caching. No objections, I will eliminate the special case. > > > > > static unsigned int pca9685_pwm_get_duty(struct pca9685 *pca, int channel) > > { > > - unsigned int off_h, val; > > + unsigned int off, on, val; > > > > if (WARN_ON(channel >= PCA9685_MAXCHAN)) { > > /* Hardware readout not supported for "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; > > } > > > > regmap_read(pca->regmap, LED_N_OFF_L(channel), &val); > > - return ((off_h & 0xf) << 8) | (val & 0xff); > > + off = ((off & 0xf) << 8) | (val & 0xff); > > + > > + if (pca->staggered_outputs) { > > + regmap_read(pca->regmap, LED_N_ON_L(channel), &val); > > + on = ((on & 0xf) << 8) | (val & 0xff); > > + > > + if (off >= on) > > + return off - on; > > + else > > + return off + PCA9685_COUNTER_RANGE - on; > > I think the if/else is unnecessary. unsigned int is twos-complement, > so we can just write: > > return (off - on) & 0xfff; (or PCA9685_COUNTER_RANGE - 1) > > and it will "magically" work even if off < on. Ah, yes of course. Good catch! > > > > + } > > + > > + return off; > > } > > As in set_duty(), consider removing the !staggered_outputs special case, > to make this function clearer and simpler. Yes, thanks. > > > > > #if IS_ENABLED(CONFIG_GPIOLIB) > > @@ -442,6 +477,9 @@ static int pca9685_pwm_probe(struct i2c_client *client, > > > > regmap_write(pca->regmap, PCA9685_MODE2, reg); > > > > + pca->staggered_outputs = device_property_read_bool( > > + &client->dev, "nxp,staggered-outputs"); > > + > > /* Disable all LED ALLCALL and SUBx addresses to avoid bus collisions */ > > regmap_read(pca->regmap, PCA9685_MODE1, ®); > > reg &= ~(MODE1_ALLCALL | MODE1_SUB1 | MODE1_SUB2 | MODE1_SUB3); > > -- > > 2.29.2 > >