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=-15.8 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 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 2AC68C433E2 for ; Mon, 29 Mar 2021 17:12:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E50396196E for ; Mon, 29 Mar 2021 17:12:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230226AbhC2RMV (ORCPT ); Mon, 29 Mar 2021 13:12:21 -0400 Received: from mail.pqgruber.com ([52.59.78.55]:57278 "EHLO mail.pqgruber.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229711AbhC2RL4 (ORCPT ); Mon, 29 Mar 2021 13:11:56 -0400 Received: from workstation.tuxnet (213-47-165-233.cable.dynamic.surfer.at [213.47.165.233]) by mail.pqgruber.com (Postfix) with ESMTPSA id CB191C729F1; Mon, 29 Mar 2021 19:11:54 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pqgruber.com; s=mail; t=1617037915; bh=Szu94hAh+X9JbhCN33k24NYs+V2mdbKnJBSTA0PXUpk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=SREAclvrF+bcBWaiWV2uGeGXWr2FkHmLLpdtfJkg2MvBq6s/eq8r1UqR0IS+h5D1M D9i2PYWnLcbdh9HY1cb1GwXl+Nz3efae4wRebqO6qpGColSSz/sRWSAJ7nbX0afnRF Ehtt2OEcdGb210kPozWAM1pP1htOxBz3NYXNhNM4= Date: Mon, 29 Mar 2021 19:11:53 +0200 From: Clemens Gruber To: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Cc: linux-pwm@vger.kernel.org, Thierry Reding , Sven Van Asbroeck , linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 2/7] pwm: pca9685: Support hardware readout Message-ID: References: <20210329125707.182732-1-clemens.gruber@pqgruber.com> <20210329125707.182732-2-clemens.gruber@pqgruber.com> <20210329165429.ookfliw4eq6zz2sg@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210329165429.ookfliw4eq6zz2sg@pengutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 29, 2021 at 06:54:29PM +0200, Uwe Kleine-König wrote: > On Mon, Mar 29, 2021 at 02:57:02PM +0200, Clemens Gruber wrote: > > Implements .get_state to read-out the current hardware state. > > > > 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 0ed1013737e3..fb026a25fb61 100644 > > --- a/drivers/pwm/pwm-pca9685.c > > +++ b/drivers/pwm/pwm-pca9685.c > > @@ -333,6 +333,46 @@ 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 = 0; > > + > > + /* 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); > > As we have PCA9685_OSC_CLOCK_MHZ = 25 this is an integer calculation > without loss of precision. It might be worth to point that out in a > comment. (Otherwise doing the division at the end might be more > sensible.) What comment do you have in mind? /* 1 integer multiplication (without loss of precision) at runtime */ ? > > > + /* 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; > > .apply uses ROUND_CLOSEST to calculate duty from state->duty_cycle, > still using / here (instead of ROUND_CLOSEST), but again as > PCA9685_OSC_CLOCK_MHZ is 25 this calculation doesn't suffer from > rounding errors. So if you feed the state returned here into .apply > again, there is (as I want it) no change. > > The only annoyance is that if PCA9685_PRESCALE holds a value smaller > than 3, .apply() will fail. Not sure there is any saner way to handle > this. According to the datasheet, "The hardware forces a minimum value that can be loaded into the PRE_SCALE register at '3'", so there should never be anything below 3 in that register. Thanks for your review! Clemens