From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 54CF7C2BB48 for ; Thu, 17 Dec 2020 17:43:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 23449235DD for ; Thu, 17 Dec 2020 17:43:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729285AbgLQRnu (ORCPT ); Thu, 17 Dec 2020 12:43:50 -0500 Received: from mail.pqgruber.com ([52.59.78.55]:55938 "EHLO mail.pqgruber.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727388AbgLQRnu (ORCPT ); Thu, 17 Dec 2020 12:43:50 -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 73C5EC727E0; Thu, 17 Dec 2020 18:43:05 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pqgruber.com; s=mail; t=1608226985; bh=6TcCAg/WkHdSeIZq4U3n4mVZZNVmTV0MBy/nU7U8pJI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=pftSHLPuTEHcNXYRK6B9oKpV4ijhodMf306IaV4P5rAwytxQ+hubaSK51zpMofj1G n5U3tejvgpyZUW851vTqTH2IbOavclEgSJCgg8zKJruu4zWEqem6jzMtYG4fS9FnYE rO/wKqevpp+PIwMjr8BCDaJ9hWXw9njs4HWC9GqQ= Date: Thu, 17 Dec 2020 18:43:04 +0100 From: Clemens Gruber To: Sven Van Asbroeck Cc: Thierry Reding , Linux Kernel Mailing List , linux-pwm@vger.kernel.org, u.kleine-koenig@pengutronix.de Subject: Re: [PATCH v5 2/7] pwm: pca9685: Support hardware readout Message-ID: References: <20201216125320.5277-1-clemens.gruber@pqgruber.com> <20201216125320.5277-2-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 11:00:59PM -0500, Sven Van Asbroeck wrote: > On Wed, Dec 16, 2020 at 7:53 AM Clemens Gruber > wrote: > > > > Implements .get_state to read-out the current hardware state. > > > > I am not convinced that we actually need this. > > Looking at the pwm core, .get_state() is only called right after .request(), > to initialize the cached value of the state. The core then uses the cached > value throughout, it'll never read out the h/w again, until the next .request(). > > In our case, we know that the state right after request is always disabled, > because: > - we disable all pwm channels on probe (in PATCH v5 4/7) > - .free() disables the pwm channel > > Conclusion: .get_state() will always return "pwm disabled", so why do we > bother reading out the h/w? If there are no plans for the PWM core to call .get_state more often in the future, we could just read out the period and return 0 duty and disabled. Thierry, Uwe, what's your take on this? > Of course, if we choose to leave the pwm enabled after .free(), then > .get_state() can even be left out! Do we want that? Genuine question, I do > not know the answer. I do not think we should leave it enabled after free. It is less complicated if we know that unrequested channels are not in use. > > > The hardware readout may return slightly different values than those > > that were set in apply due to the limited range of possible prescale and > > counter register values. > > > > Also note that although the datasheet mentions 200 Hz as default > > frequency when using the internal 25 MHz oscillator, the calculated > > period from the default prescaler register setting of 30 is 5079040ns. > > > > Signed-off-by: Clemens Gruber > > --- > > drivers/pwm/pwm-pca9685.c | 41 +++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 41 insertions(+) > > > > diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c > > index 1b5b5fb93b43..b3398963c0ff 100644 > > --- a/drivers/pwm/pwm-pca9685.c > > +++ b/drivers/pwm/pwm-pca9685.c > > @@ -331,6 +331,46 @@ static int pca9685_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, > > return 0; > > } > > > > +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 long long duty; > > + unsigned int val; > > + > > + /* Calculate (chip-wide) period from prescale value */ > > + regmap_read(pca->regmap, PCA9685_PRESCALE, &val); > > + state->period = (PCA9685_COUNTER_RANGE * 1000 / PCA9685_OSC_CLOCK_MHZ) * > > + (val + 1); > > + > > + /* The (per-channel) polarity is fixed */ > > + state->polarity = PWM_POLARITY_NORMAL; > > + > > + if (pwm->hwpwm >= PCA9685_MAXCHAN) { > > + /* > > + * The "all LEDs" channel does not support HW readout > > + * Return 0 and disabled for backwards compatibility > > + */ > > + state->duty_cycle = 0; > > + state->enabled = false; > > + return; > > + } > > + > > + duty = pca9685_pwm_get_duty(pca, pwm->hwpwm); > > + > > + state->enabled = !!duty; > > + if (!state->enabled) { > > + state->duty_cycle = 0; > > + return; > > + } else if (duty == PCA9685_COUNTER_RANGE) { > > + state->duty_cycle = state->period; > > + return; > > + } > > + > > + duty *= state->period; > > + state->duty_cycle = duty / PCA9685_COUNTER_RANGE; > > +} > > + > > static int pca9685_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm) > > { > > struct pca9685 *pca = to_pca(chip); > > @@ -353,6 +393,7 @@ static void pca9685_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm) > > > > static const struct pwm_ops pca9685_pwm_ops = { > > .apply = pca9685_pwm_apply, > > + .get_state = pca9685_pwm_get_state, > > .request = pca9685_pwm_request, > > .free = pca9685_pwm_free, > > .owner = THIS_MODULE, > > -- > > 2.29.2 > >