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=-6.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_NEOMUTT autolearn=ham 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 8C421C4360F for ; Tue, 12 Mar 2019 07:27:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 634212147C for ; Tue, 12 Mar 2019 07:27:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727071AbfCLH1i (ORCPT ); Tue, 12 Mar 2019 03:27:38 -0400 Received: from metis.ext.pengutronix.de ([85.220.165.71]:55807 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726463AbfCLH1h (ORCPT ); Tue, 12 Mar 2019 03:27:37 -0400 Received: from pty.hi.pengutronix.de ([2001:67c:670:100:1d::c5]) by metis.ext.pengutronix.de with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1h3bov-0007H9-W7; Tue, 12 Mar 2019 08:27:29 +0100 Received: from ukl by pty.hi.pengutronix.de with local (Exim 4.89) (envelope-from ) id 1h3bou-0003XE-Qq; Tue, 12 Mar 2019 08:27:28 +0100 Date: Tue, 12 Mar 2019 08:27:28 +0100 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= To: Thierry Reding Cc: Yash Shah , palmer@sifive.com, linux-pwm@vger.kernel.org, linux-riscv@lists.infradead.org, robh+dt@kernel.org, mark.rutland@arm.com, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, sachin.ghadi@sifive.com, paul.walmsley@sifive.com Subject: Re: [PATCH v5 2/2] pwm: sifive: Add a driver for SiFive SoC PWM Message-ID: <20190312072728.dy26cg4cateumuug@pengutronix.de> References: <1548762199-7065-1-git-send-email-yash.shah@sifive.com> <1548762199-7065-3-git-send-email-yash.shah@sifive.com> <20190207101657.rfzcq6xdv6ocvubg@pengutronix.de> <20190213123703.GE647@ulmo> <20190214155903.7h3b7v3nbhj57uy2@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190214155903.7h3b7v3nbhj57uy2@pengutronix.de> User-Agent: NeoMutt/20170113 (1.7.2) X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::c5 X-SA-Exim-Mail-From: ukl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Thu, Feb 14, 2019 at 04:59:03PM +0100, Uwe Kleine-König wrote: > On Wed, Feb 13, 2019 at 01:37:03PM +0100, Thierry Reding wrote: > > On Thu, Feb 07, 2019 at 11:16:57AM +0100, Uwe Kleine-König wrote: > > > On Tue, Jan 29, 2019 at 05:13:19PM +0530, Yash Shah wrote: > > [...] > > > > diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c > > [...] > > > > + writel(val, pwm->regs + PWM_SIFIVE_PWMCFG); > > > > + > > > > + writel(frac, pwm->regs + PWM_SIFIVE_PWMCMP0 + dev->hwpwm * SIZE_PWMCMP); > > > > + > > > > + val &= ~(1 << PWM_SIFIVE_PWMCFG_DEGLITCH); > > > > + writel(val, pwm->regs + PWM_SIFIVE_PWMCFG); > > > > + > > > > + pwm_sifive_get_state(chip, dev, state); > > > > > > Thierry: This changes the pwm_state. Is this how this should be done? > > > > Yes, I think that's fine. The PWM state should always reflect the > > current hardware state. If the configuration that we program does not > > reflect the state that was requested, that should be reflected in the > > PWM state. > > I'm not sure you blessed what is really done here. If I do: > > state.duty_cycle = state.period; > pwm_apply_state(pwm, &state); > > the call in question doesn't only result in pwm->state.duty_cycle < > pwm->state.period, but it also corrects my local state variable (i.e. I > have state.duty_cycle < state.period afterwards). > > Is this what you thought to be fine? I thought a bit about this and I'm convinced that updating struct pwm_device::state is/might be fine, but changing the caller's struct pwm_state that was passed to pwm_apply_state is not. Consider a consumer who does: #define PERIOD 5000000 #define DUTY_LITTLE 10 ... struct pwm_state state = { .period = PERIOD, .duty_cycle = DUTY_LITTLE, .polarity = PWM_POLARITY_NORMAL, .enabled = true, }; pwm_apply_state(mypwm, &state); ... state.duty_cycle = PERIOD / 2; pwm_apply_state(mypwm, &state); I think the second request should have state.period = 5000000 and not some other value (that might only have chosen by the respective driver because the first duty cycle was so short). Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |