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=-8.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 02782C433E6 for ; Mon, 31 Aug 2020 11:29:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D7D1820707 for ; Mon, 31 Aug 2020 11:29:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="FEi57b8R" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726446AbgHaL2i (ORCPT ); Mon, 31 Aug 2020 07:28:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45558 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726924AbgHaL1e (ORCPT ); Mon, 31 Aug 2020 07:27:34 -0400 Received: from mail-ej1-x642.google.com (mail-ej1-x642.google.com [IPv6:2a00:1450:4864:20::642]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 85ED4C0619D0; Mon, 31 Aug 2020 04:14:28 -0700 (PDT) Received: by mail-ej1-x642.google.com with SMTP id b17so7916585ejq.8; Mon, 31 Aug 2020 04:14:28 -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=X01LvFXFueRcI2ZlU9XeqbPTzDVMYa+4OS/23RAvwKo=; b=FEi57b8RlVkzPZvNuNN7nPhUzXSlgnXhuytyGSPKiFSMVEc9kpojXWHL7SL+APG5vP B0FZmBkP38k2jWlalIGtXGjMhVM+e+Q7Bx/C6RA2DKb1Ki6WVLULMIVWOKCHBWK21OAb 1DZyyc25lSAHHfRcLYTHcE3t9AE2W4x3mv7kf5Lin/qpgSxvC6XieHEKuSV7/2GVhx0J aImwsdzkb5kCEfXWUFGQJ1avl0u/1Tty0+9gJ+vQOMUAuLoMa3LXpRV2AN55BnjRHRKa 5p2bf1qK09WSl9RGi8DeVSGNM4TZc15yTaHh/pNugf5yU1LPbED6W56FSNF3FCVkxHU0 wEmg== 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=X01LvFXFueRcI2ZlU9XeqbPTzDVMYa+4OS/23RAvwKo=; b=cT9fRDoQ5Bo3MSiq98O9tlVk+BYAOzv2BWq2Lhyr9ZeGSWwTvBXYk9qc+lhbzjC/xu +BEI4EKFgmclbNmFp6Hly7QAcP2hGrbEOpv3AakusVHKR7FGKqZmfJbKTXNQqwS9WFG4 nhJvfNVf/6eEQMcasfgNwqP5Tq18yAuLTQia80Hlqq39ACbPg7Hw2pp4NRgdJYp+TTWW HnklyZAb/prVYIeB3nVAnD8oT4bfXTlVKiODNZuP8cbrqLizGHv05xfzeWOrzGZWw+jg v0uNRQz0olYDK4HcZEMEPRo4SU4iwPrbHtAcyN79okT/mWMTfzAIus5OSR2vhsGCzIAx /K1Q== X-Gm-Message-State: AOAM531Az4JwuO/TEnm05xxACmg7ZLzj3K8rEiYqDpQsCs63Kn5d9MQY IDc5d/14a3/6HEUWJId6Ln4= X-Google-Smtp-Source: ABdhPJwianpUVafwqpi+1jPvnzk6IyxvTYuhXEJ+rOOom5+IAAvmkMeA6Nv+4Vx0aPY/4m56CcsZ3Q== X-Received: by 2002:a17:906:f897:: with SMTP id lg23mr651887ejb.124.1598872467235; Mon, 31 Aug 2020 04:14:27 -0700 (PDT) Received: from localhost ([62.96.65.119]) by smtp.gmail.com with ESMTPSA id m24sm7788005eje.80.2020.08.31.04.14.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 31 Aug 2020 04:14:26 -0700 (PDT) Date: Mon, 31 Aug 2020 13:14:25 +0200 From: Thierry Reding To: Hans de Goede Cc: Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Ville =?utf-8?B?U3lyasOkbMOk?= , "Rafael J . Wysocki" , Len Brown , linux-pwm@vger.kernel.org, intel-gfx , dri-devel@lists.freedesktop.org, Andy Shevchenko , Mika Westerberg , linux-acpi@vger.kernel.org Subject: Re: [PATCH v8 08/17] pwm: crc: Fix period / duty_cycle times being off by a factor of 256 Message-ID: <20200831111425.GG1688464@ulmo> References: <20200830125753.230420-1-hdegoede@redhat.com> <20200830125753.230420-9-hdegoede@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="/Zw+/jwnNHcBRYYu" Content-Disposition: inline In-Reply-To: <20200830125753.230420-9-hdegoede@redhat.com> User-Agent: Mutt/1.14.6 (2020-07-11) Sender: linux-acpi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org --/Zw+/jwnNHcBRYYu Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sun, Aug 30, 2020 at 02:57:44PM +0200, Hans de Goede wrote: > While looking into adding atomic-pwm support to the pwm-crc driver I > noticed something odd, there is a PWM_BASE_CLK define of 6 MHz and > there is a clock-divider which divides this with a value between 1-128, > and there are 256 duty-cycle steps. >=20 > The pwm-crc code before this commit assumed that a clock-divider > setting of 1 means that the PWM output is running at 6 MHZ, if that > is true, where do these 256 duty-cycle steps come from? >=20 > This would require an internal frequency of 256 * 6 MHz =3D 1.5 GHz, that > seems unlikely for a PMIC which is using a silicon process optimized for > power-switching transistors. It is way more likely that there is an 8 > bit counter for the duty cycle which acts as an extra fixed divider > wrt the PWM output frequency. >=20 > The main user of the pwm-crc driver is the i915 GPU driver which uses it > for backlight control. Lets compare the PWM register values set by the > video-BIOS (the GOP), assuming the extra fixed divider is present versus > the PWM frequency specified in the Video-BIOS-Tables: >=20 > Device: PWM Hz set by BIOS PWM Hz specified in VBT > Asus T100TA 200 200 > Asus T100HA 200 200 > Lenovo Miix 2 8 23437 20000 > Toshiba WT8-A 23437 20000 >=20 > So as we can see if we assume the extra division by 256 then the register > values set by the GOP are an exact match for the VBT values, where as > otherwise the values would be of by a factor of 256. >=20 > This commit fixes the period / duty_cycle calculations to take the > extra division by 256 into account. >=20 > Reviewed-by: Andy Shevchenko > Signed-off-by: Hans de Goede > --- > Changes in v3: > - Use NSEC_PER_USEC instead of adding a new (non-sensical) NSEC_PER_MHZ d= efine > --- > drivers/pwm/pwm-crc.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) Acked-by: Thierry Reding --/Zw+/jwnNHcBRYYu Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEEiOrDCAFJzPfAjcif3SOs138+s6EFAl9M25EACgkQ3SOs138+ s6GH8xAAjMo/M+ShCe5lfOAZJTXx9VgYTRYj/q1jrMtkTKQI89rLA2vj+RXkHMY3 Q/vbefQxtubkKj0G85UhahEhAJ4WI03Wg18LxBA4EgkyyYtrWY0BpSa/0HnCOpTL +1nBBty7TShZZYWDjhS2eRmRuM8kLPVfSG998SJ80Yk5fNpg7lWsih26uVftL2jC eOCDl8GxAN6bRn3f2sly5fKH+uhIjHYg5B18pVZ1MdkwpIY7BtYLNWQsd1VXvb+I SO0REjIpB8UVzQZ11Ea3sUrZhNMu/x2P6J93VuGxCfkMZMM3BpwDeLAfyM/sW0Ko Kc0YiedvxaD10jvTKXbVhZCL3N9sV0eh3zNPOOL/Vxw0OOTafwbyoDrpxQVGJp3A LUOsz+5GeuSM/JyEMHAGq/JYxdPyLDX/ZgWEJzUvWwhCJFQ+4K4c10Ri1qITTVSQ +gn6Rn3pf/SjlrZJ6loA8K/Yi4ndfmrfl/KeJ81TeTOYZVBrma6W6NFFQpUwI+PD SDXskyBVU5T8v+rd2AzN5nM1ubFH4p3y5dqzdzX1uz5MC9aRTwFV17g44Q3FY8HL qfPoPgeSoA0o7jxf63aTVYgqXcnSJ8Bg9fZ/POn/s/GXAcB+bV0apJYFWwQ/Tgg9 bZ67o0uSIfAKKR0sNxPHU/Hd/kzQ7W+4zCkxbx377zuSi7wf5yc= =JLKH -----END PGP SIGNATURE----- --/Zw+/jwnNHcBRYYu--