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=-6.7 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,USER_AGENT_SANE_1 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 0D1E4C433FE for ; Fri, 4 Dec 2020 11:40:12 +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 93FCF2251D for ; Fri, 4 Dec 2020 11:40:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 93FCF2251D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=mess.org 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-Transfer-Encoding: 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-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=KHSCYMUtyETZYZqRVcZeKEcDF4uBHEsCFlICEhQ9dhg=; b=Qya2Cbrwn92FPckYdDFyNNCu7 8jok30IROrx6e44PdMaWiG53YzQPqF10wyJJGQU94G8Tm161PtpKvsCNvd95HA8tB/kG2VqozDMKb ypUA95hFtbmefMFKKUO/Kr/IElP9+FvXw/s46XOhxQ87Umk6So9gIUAc9xowlyvD7Iv2Pyk8/1xA+ LmW2hg19kK0LoeHD+Yo95MITtXkTXtIJLZmnG9o+VJ+6B4EcquYWMWIbT7YCm/atX5wla461h3HN4 Sdk57W40wI0yIdJgaM4Jpe0TzIQUyG7YRS7bAdJqEAcwSQPdjtjXxmD1BJUdPoKrNQuxkoEI5JdVp 44OQJpi+A==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kl9QM-0000DN-A3; Fri, 04 Dec 2020 11:38:54 +0000 Received: from gofer.mess.org ([2a02:8011:d000:212::1]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kl9QJ-0000CV-0y; Fri, 04 Dec 2020 11:38:52 +0000 Received: by gofer.mess.org (Postfix, from userid 1000) id 2613AC63B3; Fri, 4 Dec 2020 11:38:47 +0000 (GMT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=mess.org; s=2020; t=1607081927; bh=Az/uDrcMyA9/dLYwyl4sQ5Fgc9q8oK/Kxxi0WSvZST4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VuaTLHk6t5PWIq8CN0UUidPilVW6Fw6sSC3EJL4dWj62vDf1kYjZJmlJFPz4zQQFS yLQWocauR2jIvec/j0HKqlxH9wgKBSMlE5y60gHsBGw/vWlQPurXXpy5h+O72xUZA4 FmRlg51yNiXA3mfHemg8p/hgd7CiuB23rczJij48Q3yIiSrESCaYrG2so7bMxr0+/I Ac5UOPYrayS3tkULu6uAw0J+LMPO3jvq7DRKfXbMQjSTJkKLUiYZZv61bLHtJyZYPv aNGbOr2KpTr4Yr1xFJ0Dztrxr2w19JxhKVtbgh3T9M0RNZvKI/7gItixlhWODJHops 5ndnB27gqImsg== Date: Fri, 4 Dec 2020 11:38:46 +0000 From: Sean Young To: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Subject: Re: [PATCH v2] pwm: bcm2835: Support apply function for atomic configuration Message-ID: <20201204113846.GA6547@gofer.mess.org> References: <202011281128.54eLfMWr-lkp@intel.com> <1606564926-19555-1-git-send-email-LinoSanfilippo@gmx.de> <20201129181050.p6rkif5vjoumvafm@pengutronix.de> <4683237c-7b40-11ab-b3c0-f94a5dd39b4d@gmx.de> <20201204084417.GA2154@gofer.mess.org> <20201204111326.qjux6k2472dmukot@pengutronix.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201204111326.qjux6k2472dmukot@pengutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201204_063851_304388_B1667D45 X-CRM114-Status: GOOD ( 32.28 ) 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: linux-arm-kernel@lists.infradead.org, linux-pwm@vger.kernel.org, f.fainelli@gmail.com, sbranden@broadcom.com, rjui@broadcom.com, linux-kernel@vger.kernel.org, Lino Sanfilippo , thierry.reding@gmail.com, linux-rpi-kernel@lists.infradead.org, bcm-kernel-feedback-list@broadcom.com, lee.jones@linaro.org, nsaenzjulienne@suse.de Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi, On Fri, Dec 04, 2020 at 12:13:26PM +0100, Uwe Kleine-K=F6nig wrote: > On Fri, Dec 04, 2020 at 08:44:17AM +0000, Sean Young wrote: > > On Fri, Dec 04, 2020 at 12:42:15AM +0100, Lino Sanfilippo wrote: > > > > You're storing an unsigned long long (i.e. 64 bits) in an u32. If > > > > you are sure that this won't discard relevant bits, please explain > > > > this in a comment for the cursory reader. > > > = > > > What about an extra check then to make sure that the period has not b= een truncated, > > > e.g: > > > = > > > value =3D DIV_ROUND_CLOSEST_ULL(state->period, scaler); > > > = > > > /* dont accept a period that is too small or has been truncated */ > > > if ((value < PERIOD_MIN) || > > > (value !=3D DIV_ROUND_CLOSEST_ULL(state->period, scaler))) > > > return -EINVAL; > > = > > Rather than doing another 64 bit division which is expensive (esp on 32= bit > > kernels), you could assign to u64 and check: > > = > > if (value < PERIOD_MIN || value > U32_MAX) > > return -EINVAL; > = > Given that value is a u32, value > U32_MAX will never trigger. I meant that value is declared u64 as well ("assign to u64"). > Maybe checking period before doing the division is more sensible. That could introduce rounding errors, exactly why PERIOD_MIN was introduced. > > > > Also note that round_closed is probably wrong, as .apply() is > > > > supposed to round down the period to the next achievable period. (B= ut > > > > fixing this has to do done in a separate patch.) > > > = > > > According to commit 11fc4edc4 rounding to the closest integer has bee= n introduced > > > to improve precision in case that the pwm controller is used by the p= wm-ir-tx driver. > > > I dont know how strong the requirement is to round down the period in= apply(), but I > > > can imagine that this may be a good reason to deviate from this rule. > > > (CCing Sean Young who introduced DIV_ROUND_CLOSEST) > > = > > There was a problem where the carrier is incorrect for some IR hardware > > which uses a carrier of 455kHz. With periods that small, rounding errors > > do really matter and rounding down might cause problems. > > = > > A policy of rounding down the carrier is not the right thing to do > > for pwm-ir-tx, and such a change will probably break pwm-ir-tx in some > > edge cases. > = > IMO it's not an option to say: pwm-driver A is used for IR, so A's > .apply uses round-nearest and pwm-driver B is used for $somethingelse, > so B's .apply uses round-down. I'm not saying that one driver should have one it one way and another driver another way. > To be a sensible API pwm_apply_state > should have a fixed behaviour. I consider round-down the sensible > choice (because it is easier to implmement the other options with this) It's not sensible when it's wrong about half the time. Why is is easier to implement? > and for consumers like the IR stuff we need to provide some more > functions to allow it selecting a better suited state. Something like: > = > pwm_round_state_nearest(pwm, { .period =3D 2198, .. }, &state) > = > which queries the hardwares capabilities and then assigns state.period = =3D > 2200 instead of 2100. This is very elaborate and surely not "easier to implement". Why not just do the right thing in the first place and round-closest? > Where can I find the affected (consumer) driver? So there is the pwm-ir-tx driver. The infrared led is directly connected to the pwm output pin, so that's all there is. Thanks, Sean _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel