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[23.128.96.18]) by mx.google.com with ESMTP id c17si3586943eds.556.2020.12.16.20.03.07; Wed, 16 Dec 2020 20:03:29 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=Wz729HH2; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727896AbgLQEBw (ORCPT + 99 others); Wed, 16 Dec 2020 23:01:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52826 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727233AbgLQEBv (ORCPT ); Wed, 16 Dec 2020 23:01:51 -0500 Received: from mail-ua1-x930.google.com (mail-ua1-x930.google.com [IPv6:2607:f8b0:4864:20::930]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 66AB1C0617A7; Wed, 16 Dec 2020 20:01:11 -0800 (PST) Received: by mail-ua1-x930.google.com with SMTP id y25so5226272uaq.7; Wed, 16 Dec 2020 20:01:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=hPoC6m5W8VLKxto4R9D3lag/KjqB9wfQE1fVcUOFbDQ=; b=Wz729HH2Z5VFq9FmqP2PgZlVCmWrdLir3bZuEHB8H7YapU9l8lUMW7lFoGENk5LEHi SytDY3Og/CLasQAdxZ4vQOFa5TkzoyTjapj4eARnEBYO4GM8vkWgNTp56g4mBevm85TP M34J/YHblpnqszTYs+YrUSDvmAPhc6U+DROCBrCqSsNRvVMDu5+WP9MFTJutCw/080mA A+yrlHiN7nbX2aZnkXmWACmtdvL5aM2X5xznfhPrXTAV3nK1kGGLmul+whAvOrXbmliQ 8+rm9+3HyM1HZ5l4h7QuHPbkWRIbgSPd08QcsbvwMKWcVe0aUt4+sqzDtrliIv8hcCCQ EeWA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=hPoC6m5W8VLKxto4R9D3lag/KjqB9wfQE1fVcUOFbDQ=; b=MkXRAjgi0Ptxc7m4O0tkWW0b2eUFaS5dM4KsUAql3oIePBI5JXfg121NfnlHmV757b 2tkPWn7MLAEvqR3iKopqiyGEoNyqRSGFm9IDPBJ2iEEPEkMciaKTsxn2VpCkcx0cLz/N c8z9G61Jz6NFElzzzMK8MBxAtB8Zg9wfKj6Vbo+PyyR3CTGXvo1DjFMvjaceVvm6PSQm FIA5hmvZSWP7Ps07wtO6BbAZbNF5ExoaOp0d3cqKqr1LbGHSNi/J3IeunL6edkgtsXnb atQkIAOjGgaoT7uVzIze0qYxyN1hxqWrbc/9fdKDBWZJm5wOVMgJzW2GvcfEi6gTzGSb yhig== X-Gm-Message-State: AOAM531FSmRg9ZQsfvBZOIPwENt2tY4unWlTKybAQUxnL+qKHT75io2t P882t2FR3NvHMzEw5/05GJQ1FtI9xfpWS5R+Qfk= X-Received: by 2002:ab0:3806:: with SMTP id x6mr22038369uav.58.1608177670487; Wed, 16 Dec 2020 20:01:10 -0800 (PST) MIME-Version: 1.0 References: <20201216125320.5277-1-clemens.gruber@pqgruber.com> <20201216125320.5277-2-clemens.gruber@pqgruber.com> In-Reply-To: <20201216125320.5277-2-clemens.gruber@pqgruber.com> From: Sven Van Asbroeck Date: Wed, 16 Dec 2020 23:00:59 -0500 Message-ID: Subject: Re: [PATCH v5 2/7] pwm: pca9685: Support hardware readout To: Clemens Gruber Cc: Thierry Reding , Linux Kernel Mailing List , linux-pwm@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? 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. > 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 >