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 E5287C433E2 for ; Mon, 31 Aug 2020 11:24:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C3B652073A for ; Mon, 31 Aug 2020 11:24:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="EKtSjKtz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727043AbgHaLYW (ORCPT ); Mon, 31 Aug 2020 07:24:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44762 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727828AbgHaLWt (ORCPT ); Mon, 31 Aug 2020 07:22:49 -0400 Received: from mail-ed1-x543.google.com (mail-ed1-x543.google.com [IPv6:2a00:1450:4864:20::543]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8FBC4C0619CD; Mon, 31 Aug 2020 04:14:01 -0700 (PDT) Received: by mail-ed1-x543.google.com with SMTP id w1so1408969edr.3; Mon, 31 Aug 2020 04:14:01 -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=FExIKAHJpPJFM3Hd44tazabRIhwd+0VFgHYZYcprPmE=; b=EKtSjKtzv24vUhMxF+gt7LwUCEObaU3gPowz0n9Rvrs8wdxgAIP+QWufXKZujYYBhU Uo3CawjQpfdgFZBlGzpSwcubxyiiNXXVDUdNI9pGzCRScHb+9Bx0Wi6AFSI38OW/MVsW mb5I7dO6ZerK1fHSeLbbvhUX8Mk7s4nXY26gGXR0ddg0f/1pkKMVDJ7n6HCmfyccD01O TznDM/nTvjkVwovGVCCZqGsAi99CkHPtrA75S8+H4pbgxqW7Agw7EvCJ4jPhT3AO0jZR VaBi0zdqGpEtCxJsbI8Y7bMV9TAgfmtiuqHV0OqjC1iMDTIKHeR6L+M0OzsqDwofuF2e eWAQ== 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=FExIKAHJpPJFM3Hd44tazabRIhwd+0VFgHYZYcprPmE=; b=fPwR34Ctgons79u596ymLdW3VpmeCHpJLICdaf3VBJ4vITwFgrVsef0b6bUFVKYL+M vT39xWD3WwxOJHmggMsVvtp7P6VlkSakzhVTBOiTLaRWwr+XVmTLe3SUL0eol0aVi62G Q+1/8SadJkM7dXw3ceJPMqs6CplrAs9pnZEioZO9PyfgZJREr0BZ90cLYLj898CYhytW DEFzsHSywk6IhSEHj4mn9iCsHECgfherS94Xg7wP38rgZKagTbH6HNqNlPB7FE01qOwS rfOrSu3BJ/S4hmpb/7i8fFpycQFaAvCWta50AsQNthF0VwfnVrhy83Pg4N4gkN8tq2Yv A9Ug== X-Gm-Message-State: AOAM5321OD2yhBESZ0d6rom0AMBzisJ1Gv03sr0fERkvAfx3qkVQuV8s S1TlhcMa8wo0QKodJIwg6ZI= X-Google-Smtp-Source: ABdhPJzSou1EakYOIg96I8GnoircE3Vn7kSNmn6F1/7zwYOg6k41dpCvAPKfpjEEd/aEdMlY9skw5w== X-Received: by 2002:aa7:d146:: with SMTP id r6mr720807edo.335.1598872440245; Mon, 31 Aug 2020 04:14:00 -0700 (PDT) Received: from localhost ([62.96.65.119]) by smtp.gmail.com with ESMTPSA id o7sm7165100edq.53.2020.08.31.04.13.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 31 Aug 2020 04:13:59 -0700 (PDT) Date: Mon, 31 Aug 2020 13:13:58 +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: <20200831111358.GF1688464@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="/QKKmeG/X/bPShih" 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 --/QKKmeG/X/bPShih 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 --/QKKmeG/X/bPShih Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEEiOrDCAFJzPfAjcif3SOs138+s6EFAl9M23UACgkQ3SOs138+ s6FFYg/+Mtzc1XwV7Zl1w99FCSgZyIrsahQ4SvPhVAXHLByxVW0Sgfi/z9K/bDcB Fjw3E5MB0XL4UD9DWtdCKefCLe/5kIlbsS/LK7BPplf1GNfctSYQ72L5soS7HKrn vBjHnIr5ohFn/EGf3RWeLczkUoFVhfbMYFgor/H1FjXo5OeHQ3Fkr2AVPsnyIYXZ Iuc7iGLT8lI57IoxRlJ7ZKu0IXImzrN7YU4a+pfZ77fBAu3B9D9jom+L+U0E+E6q Y+ZBnaRVz13j6OSRMtfu13/kATzx1HgJZfjmMiimldrXbucWCovYXK2GWz8RJp5J YrXCFi8WdHdxB/JxDSYsswynJtRiSmGTjQmvxy6GYXZe8IvSB3VkpaTkQS5bzA65 QAYAclX3dnxT46eQ+yiNH4WEWlgL5gxsLeOMCvFWa5Lismv4q2gvxjBTF0RapKaD oncskpQfC4HlP1vQieYkUrYQUfAq+Gq2a6OU5qk0HES6N504YLAhS35xqHvWvT+9 QT50ulvZJVyUzZN9HgmMphXKi0jTeJ5dAZjdf8RbzIXD8hBlFJbObnPl6Xk2VRh2 kJSwxDm74OT4sD2IydJQQCBnOtf6MZ/HjfLa5M6UP34DyWKg5LTlUbBDjp5+cJcs jrZ53SdqyD8MbZ/0meG1wcRvneBbIEKkPtAkowDRt2wkQHEO6nc= =4Oyz -----END PGP SIGNATURE----- --/QKKmeG/X/bPShih--