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=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 5BDE5C433DF for ; Fri, 7 Aug 2020 10:26:24 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 295EF2075D for ; Fri, 7 Aug 2020 10:26:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="wWXZbDRx" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 295EF2075D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=pengutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Type:Cc: List-Subscribe:List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id: In-Reply-To:MIME-Version:References:Message-ID:Subject:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Z5lTqNhThGEg5XgI0KdBPS3V+Nk/13CCs0t3V3Z5XCs=; b=wWXZbDRxTV6qI6XPM4xVsasZ2 FCU46TUCUFHSSxq9BETTvbN0C+/rk4B9lRVO4GJ1OME5TdfFruG8Gs+QZkdPqASbbO0w/2EXZ1FyR X2qaryuCxVt7XQC7dD7fIErCxoQObZUiaj9pna21qlxbXQ1dr/4uUa88X1mI0hgXJnRDQOWX+mrul YvEppZABpyGY19ujFSdPj4zdGIaodmb1hTWZLoyXZ9IY6DB1CQ37X2sXDztwkKVFZQPXq1Wr81lto fpDCw1GaTer5E/g/17UQh/Mr/ZANpE8/L+6Kr1tmZJuvLeMjvqmzasDmgc3s5DN3IfZX94WP6hQmi i0XX8NGVg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k3zYY-0002wB-HG; Fri, 07 Aug 2020 10:24:58 +0000 Received: from metis.ext.pengutronix.de ([2001:67c:670:201:290:27ff:fe1d:cc33]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1k3zYW-0002vi-D7 for linux-arm-kernel@lists.infradead.org; Fri, 07 Aug 2020 10:24:57 +0000 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 4.92) (envelope-from ) id 1k3zYO-0001jw-TK; Fri, 07 Aug 2020 12:24:48 +0200 Received: from ukl by pty.hi.pengutronix.de with local (Exim 4.89) (envelope-from ) id 1k3zYI-0003e8-3P; Fri, 07 Aug 2020 12:24:42 +0200 Date: Fri, 7 Aug 2020 12:24:41 +0200 From: Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= To: Michael Walle Subject: Re: [PATCH v7 06/13] pwm: add support for sl28cpld PWM controller Message-ID: <20200807102441.qcshhsc36nzj7bpn@pengutronix.de> References: <20200803093559.12289-1-michael@walle.cc> <20200803093559.12289-7-michael@walle.cc> <20200806084000.k3aj5nmqdodmb35v@pengutronix.de> <20200807074543.pfbwlhtegl3oc4zp@pengutronix.de> <92116be9aa56250becc4019c6c7a1538@walle.cc> MIME-Version: 1.0 In-Reply-To: <92116be9aa56250becc4019c6c7a1538@walle.cc> 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-arm-kernel@lists.infradead.org X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200807_062456_529129_9695BB4D X-CRM114-Status: GOOD ( 30.41 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: devicetree@vger.kernel.org, Catalin Marinas , Linus Walleij , Thierry Reding , Pavel Machek , Lee Jones , Jason Cooper , Andy Shevchenko , Marc Zyngier , Bartosz Golaszewski , Guenter Roeck , linux-pwm@vger.kernel.org, Jean Delvare , linux-watchdog@vger.kernel.org, Will Deacon , linux-gpio@vger.kernel.org, Mark Brown , Thomas Gleixner , Wim Van Sebroeck , linux-arm-kernel@lists.infradead.org, linux-hwmon@vger.kernel.org, Greg Kroah-Hartman , linux-kernel@vger.kernel.org, Li Yang , Rob Herring , Shawn Guo Content-Type: multipart/mixed; boundary="===============0752287093953846788==" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org --===============0752287093953846788== Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="ui3bvps5z2hxjh32" Content-Disposition: inline --ui3bvps5z2hxjh32 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi Michael, On Fri, Aug 07, 2020 at 09:55:19AM +0200, Michael Walle wrote: > Am 2020-08-07 09:45, schrieb Uwe Kleine-K=F6nig: > > On Fri, Aug 07, 2020 at 09:28:31AM +0200, Michael Walle wrote: > > > Am 2020-08-06 10:40, schrieb Uwe Kleine-K=F6nig: > > > > On Mon, Aug 03, 2020 at 11:35:52AM +0200, Michael Walle wrote: > > > > > +static void sl28cpld_pwm_get_state(struct pwm_chip *chip, > > > > > + struct pwm_device *pwm, > > > > > + struct pwm_state *state) > > > > > +{ > > > > > + struct sl28cpld_pwm *priv =3D dev_get_drvdata(chip->dev); > > > > > + unsigned int reg; > > > > > + int prescaler; > > > > > + > > > > > + sl28cpld_pwm_read(priv, SL28CPLD_PWM_CTRL, ®); > > > > > + > > > > > + state->enabled =3D reg & SL28CPLD_PWM_CTRL_ENABLE; > > > > > + > > > > > + prescaler =3D FIELD_GET(SL28CPLD_PWM_CTRL_PRESCALER_MASK, reg); > > > > > + state->period =3D SL28CPLD_PWM_PERIOD(prescaler); > > > > > + > > > > > + sl28cpld_pwm_read(priv, SL28CPLD_PWM_CYCLE, ®); > > > > > + state->duty_cycle =3D SL28CPLD_PWM_TO_DUTY_CYCLE(reg); > > > > > > > > Should reg be masked to SL28CPLD_PWM_CYCLE_MAX, or is it guaranteed= that > > > > the upper bits are zero? > > >=20 > > > Mh, the hardware guarantees that bit7 is zero. So masking with > > > SL28CPLD_PWM_CYCLE_MAX won't buy us much. But what I could think > > > could go wrong is this: someone set the prescaler to !=3D 0 and the > > > duty cycle to a value greater than the max value for this particular > > > prescaler mode. For the above calculations this would result in a > > > duty_cycle greater than the period, if I'm not mistaken. > > >=20 > > > The behavior of the hardware is undefined in that case (at the moment > > > it will be always on, I guess). So this isn't a valid setting. > > > Nevertheless it might happen. So what about the following: > > >=20 > > > state->duty_cycle =3D min(state->duty_cycle, state->period); > >=20 > > If you care about this: This can also happen (at least shortly) in > > sl28cpld_pwm_apply() as you write SL28CPLD_PWM_CTRL before > > SL28CPLD_PWM_CYCLE there. >=20 > It could also happen if it was the other way around, couldn't it? > Changing modes might glitch. If you want to prevent this, you have to order the writes depending on prescaler increasing or decreasing. Best regards Uwe --=20 Pengutronix e.K. | Uwe Kleine-K=F6nig | Industrial Linux Solutions | https://www.pengutronix.de/ | --ui3bvps5z2hxjh32 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAABCgAdFiEEfnIqFpAYrP8+dKQLwfwUeK3K7AkFAl8tK+YACgkQwfwUeK3K 7Am+ZAf/fEspbQK7oTVzKrTHBQXxu0AjknqY6yLOlTFthBSsQqbzGwekDnDjQG21 Emw2dyTCQW7YHQaYx8l1HilDsVFiazBpJ6yG49upduH83s15tgAB4Guv2uTbrzim uMsqxPDtiCrjGdTw4MNt37OoKh0A2O+IAd1yuSrgDpQqWiDM0uNs+MMNZm8OQAST ZkVhwCFr28b9QNzUodg6d2QK5T5DWEgt6BFkPpn5SFUc/mMMQs2/3LcaBOh2Gd9/ FqKla8k4Akpniv4OcC93n0QfOap22V69gLflWJLN2YB3Gn+BvZLqMvhAgF6cy/Ho jEP7yLYqhcfx644/uGqeHpOHNDm8Eg== =jSvw -----END PGP SIGNATURE----- --ui3bvps5z2hxjh32-- --===============0752287093953846788== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel --===============0752287093953846788==--