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=-14.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 DFF0BC433C1 for ; Mon, 22 Mar 2021 10:48:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A84DE61983 for ; Mon, 22 Mar 2021 10:48:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230087AbhCVKsX (ORCPT ); Mon, 22 Mar 2021 06:48:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57826 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230273AbhCVKsP (ORCPT ); Mon, 22 Mar 2021 06:48:15 -0400 Received: from mail-wr1-x42f.google.com (mail-wr1-x42f.google.com [IPv6:2a00:1450:4864:20::42f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F209AC061574 for ; Mon, 22 Mar 2021 03:48:14 -0700 (PDT) Received: by mail-wr1-x42f.google.com with SMTP id k8so16131170wrc.3 for ; Mon, 22 Mar 2021 03:48:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=GmJxNHFaY39dVIye6EG6NKmGClXvquEfYdu615kK6QM=; b=RJxZ1uRgek0n+/tcRm6YHxfkpu1yJl21EPPYlTvlvfERGEq6VZA3XZZp85tm3JoiC8 GWQWL9ABEj/3kbO9AoRA6/R0xYX5f9/yHTkGgBXSGEtVUkKtmwrUVl18izq6aJMT7vr6 BfhXafdAx6Heb4VtDRnEQg1vMuH2dr+XIoJDSmvqhG/a2EuWoLGVCmmUVehGSO5VA42x I2GE46uTaeEZ6io6/vE6XWKpunLLp/NH9myHVbAInIUlPvZRWNElO1vkiaVpMoyBHMZX dpRWdX0wpDToOHSW56huwyrejHy3DD4E3+1Gl02VGoAvxO2iotXdpjcvstz2KTe03AIW EyHw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=GmJxNHFaY39dVIye6EG6NKmGClXvquEfYdu615kK6QM=; b=N8jbTdicxwLo2ZnCcv4CT9x1MSwY++vcQU17DO22zW/yNWoWDEJsnKXP7hGwNsdshz 1Z7PLWF0/tO4zY1RiTO3K61OXTdj9zTlKZEUSqAbqRuHLsVIGRLCh86h8fB7NXa71l0K tezjiw9bp6o236JK8Wf5BdIGGbhPDh7WHNzObKG23KI3uAEaS0UnUt4YzqNsPHjWzdLr fQwCSV0EborO3UisMWIKwa001Hfzz9u7+nuqbuyYS80N+b5cO0FtfpjBMuoNPHYyFvyS xDthfDz5rmuqRcEqL4qITQcOqGjM3PHGZmP/L1IQZfBXK846X+ns09KZCTVfUafbbKd0 lm1A== X-Gm-Message-State: AOAM532Y5y4IPYqbVWRKpAg3evcVnpDWbfwakHXzUQjkduugPU9mwvjM D571yzqSWJDpA0kpbomRJZCieAu54Jc= X-Google-Smtp-Source: ABdhPJzFulOcxIrFpshmEUF4BF/RD5c7qzRj7p5kTzfi6TJjE4T5I3AvULO3qog8BJSdVJXz+NMhUw== X-Received: by 2002:adf:83c2:: with SMTP id 60mr17427883wre.386.1616410093732; Mon, 22 Mar 2021 03:48:13 -0700 (PDT) Received: from localhost ([62.96.65.119]) by smtp.gmail.com with ESMTPSA id i8sm19186507wrx.43.2021.03.22.03.48.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Mar 2021 03:48:12 -0700 (PDT) Date: Mon, 22 Mar 2021 11:48:30 +0100 From: Thierry Reding To: Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= Cc: Lee Jones , Nicolas Saenz Julienne , Florian Fainelli , Ray Jui , Scott Branden , Lino Sanfilippo , Sean Young , linux-pwm@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com, linux-rpi-kernel@lists.infradead.org, kernel@pengutronix.de Subject: Re: [PATCH v3] pwm: bcm2835: Improve period and duty cycle calculation Message-ID: References: <20210114204804.143892-1-u.kleine-koenig@pengutronix.de> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="VQ8zwhowAqeKB/rU" Content-Disposition: inline In-Reply-To: <20210114204804.143892-1-u.kleine-koenig@pengutronix.de> User-Agent: Mutt/2.0.6 (98f8cb83) (2021-03-06) Precedence: bulk List-ID: X-Mailing-List: linux-pwm@vger.kernel.org --VQ8zwhowAqeKB/rU Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Jan 14, 2021 at 09:48:04PM +0100, Uwe Kleine-K=C3=B6nig wrote: > With an input clk rate bigger than 2000000000, scaler would have been > zero which then would have resulted in a division by zero. >=20 > Also the originally implemented algorithm divided by the result of a > division. This nearly always looses precision. Consider a requested period > of 1000000 ns. With an input clock frequency of 32786885 Hz the hardware > was configured with an actual period of 983869.007 ns (PERIOD =3D 32258) > while the hardware can provide 1000003.508 ns (PERIOD =3D 32787). > And note if the input clock frequency was 32786886 Hz instead, the hardwa= re > was configured to 1016656.477 ns (PERIOD =3D 33333) while the optimal > setting results in 1000003.477 ns (PERIOD =3D 32787). >=20 > This patch implements proper range checking and only divides once for > the calculation of period (and similar for duty_cycle). >=20 > Signed-off-by: Uwe Kleine-K=C3=B6nig > --- > Hello, >=20 > changes since v2 (Message-Id: > 20201222221319.2101107-1-u.kleine-koenig@pengutronix.de): >=20 > - Add my calculation to the comment explaining the max_period formula > as discussed with Lino. >=20 > Best regards > Uwe >=20 > drivers/pwm/pwm-bcm2835.c | 35 +++++++++++++++++++++++++++-------- > 1 file changed, 27 insertions(+), 8 deletions(-) Applied, thanks. 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