From mboxrd@z Thu Jan 1 00:00:00 1970 From: Felipe Balbi Subject: Re: [PATCH] i2c: omap: improve duty cycle on SCL Date: Thu, 18 Jun 2015 12:24:28 -0500 Message-ID: <20150618172428.GB27790@saruman.tx.rr.com> References: <1434482276-1210-1-git-send-email-balbi@ti.com> <55815581.80807@gmx.de> <20150617153812.GB18421@saruman.tx.rr.com> <5582678F.4010505@gmx.de> Reply-To: Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="32u276st3Jlj2kUU" Return-path: Received: from bear.ext.ti.com ([192.94.94.41]:32965 "EHLO bear.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754679AbbFRR1a (ORCPT ); Thu, 18 Jun 2015 13:27:30 -0400 Content-Disposition: inline In-Reply-To: <5582678F.4010505@gmx.de> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: Michael Lawnick Cc: balbi@ti.com, wsa@the-dreams.de, Tony Lindgren , Nishanth Menon , Dave Gerlach , linux-i2c@vger.kernel.org, Linux OMAP Mailing List , Linux ARM Kernel Mailing List --32u276st3Jlj2kUU Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Jun 18, 2015 at 08:39:11AM +0200, Michael Lawnick wrote: > Am 17.06.2015 um 17:38 schrieb Felipe Balbi: > >Hi, > > > >On Wed, Jun 17, 2015 at 01:09:53PM +0200, Michael Lawnick wrote: > >>Am 16.06.2015 um 21:17 schrieb Felipe Balbi: > >>>With this patch we try to be as close to 50% > >>>duty cycle as possible. The reason for this > >>>is that some devices present an erratic behavior > >>>with certain duty cycles. > >>> > >>>One such example is TPS65218 PMIC which fails > >>>to change voltages when running @ 400kHz and > >>>duty cycle is lower than 34%. > >>> > >>>The idea of the patch is simple: > >>> > >>>calculate desired scl_period from requested scl > >>>and use 50% for tLow and 50% for tHigh. > >>... > >>Hmm, and what's about Philips I2C specification 2.1, Jan 2000, Table 5? > >> > >>>PARAMETER SYMBOL STANDARD-MODE FAST-MODE = UNIT > >>> MIN. MAX. MIN. MAX. > >>>LOW period of the SCL clock tLOW 4.7 =E2=80=93 1.3 = =E2=80=93 =C2=B5s > >>>HIGH period of the SCL clock tHIGH 4.0 =E2=80=93 0.6 = =E2=80=93 =C2=B5s > >> > >>Your signal is in spec (0.85 =C2=B5s high, 1,65 low). > >>Maybe your TPS65218 is just buggy or signals are bad? > > > >yes, tps is buggy, it's written in the commit log itself. > > >=20 > So I think it is unacceptable to change the adapters code violating > specification because some buggy device doesn't work properly. read the other thread and you'll see that it's not violating jack > This change for your device has chance to blow up many correctly > working ones. How ? --=20 balbi --32u276st3Jlj2kUU Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJVgv7MAAoJEIaOsuA1yqREHTMP/2MVCa56nikZatPn+6+D9RGJ YdCXDehifA0jjHWfv6CLivqFmHR2gK6Ohx/XhZv5cJXhtgr14nc321kZEy1UrpRX 8Fn4V0zN0kPvKKF8iznWkBdLdjTBEceRjERSSaXiYMlj3seK3CFoQ3oSmifCn3Uo cq3JrRRxDNxbfyJmyu0tWyIXgP6L7/bSLOFo6XdyUL5M9fAj2/ChaES9RkiPx48r dCOnhN0Zzz89uWhIKqseh3knRirGHyIbK2Xl2kHXpbeNLK86hKw0VI6XyKJcuxnG 4JVH7afkXkRFp9x8nHHnJQ/vVFWS74Q7avDK7JqT1Km9BSAhsD042qF4I7VSwoAx Jzr8oobAlN2C/ZhZG1QKtSklq1He7y1zqp6m81aCt9m4QEWuQdqowR2q4qOHL/4n fN3+vDQXx8M5z2bQd+xWqc6EdELu4xThvLUvI34Gb3dCTpi/1zo39LMAoujuG2+i cV9FXCwwg/4/JfhBK+F9zPOIAkug6vWpSGC4XMGsWC2oqMZqA22kof7ZuKCJ8P2O vW2x78ufk05WNnrbHct4Ucxb6lb3z2/Ypc1DigCkkh8kaJ4rCVRBP62gMJ6AvCxr ZP7HJiWD+ETaFuyaZlkvmr6HIXAdwoBSmWV6BtpA/choijf2K6BOgQMBC0tKHYv0 gSr0i+96o3lpiEPUVGtv =KshA -----END PGP SIGNATURE----- --32u276st3Jlj2kUU--