From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Zimmermann Subject: Re: [PATCH] i2c: Raise SDA for each received bit, if necessary Date: Thu, 12 May 2016 18:19:12 +0200 Message-ID: <5734AD00.3050904@users.sourceforge.net> References: <1461780714-20378-1-git-send-email-tdz@users.sourceforge.net> <20160512090544.GB1638@katana> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Return-path: Received: from mail-wm0-f42.google.com ([74.125.82.42]:38026 "EHLO mail-wm0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932086AbcELQTk (ORCPT ); Thu, 12 May 2016 12:19:40 -0400 In-Reply-To: <20160512090544.GB1638@katana> Sender: linux-i2c-owner@vger.kernel.org List-Id: linux-i2c@vger.kernel.org To: Wolfram Sang Cc: linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org Hi Am 12.05.2016 um 11:05 schrieb Wolfram Sang: > Hi Thomas, > > On Wed, Apr 27, 2016 at 08:11:54PM +0200, Thomas Zimmermann wrote: >> Some I2C adapters don't raise SDA by themselves when sending a bit. This >> behavior can be seen with the DDC channel of SiS 300 graphics cards. > > I think you mean 'clients' or 'devices' here, not adapters (masters), > right? Yes, sorry. > So, it seems you have a bus without a pull-up resistor (or a > broken one?) but use now a push-pull design. This is against the I2C > standard and for most circiuts quite dangerous as it can lead to > shortcuts. I see. > Do you have any hints that the bus is designed this way? In which driver > do you want to use the new flag? I was playing with the DRM framework and an old SiS graphics card. I discovered this issue while trying to read the EDID from the monitor. I have a few other SiS cards/models here and they all expose this behavior. So I guess it's intentional(==cheaper?), although the HW docs don't seem mention it explicitly. Best regards Thomas > > Thanks, > > Wolfram > -- GnuPG: http://tdz.users.sourceforge.net/tdz.asc Fingerprint: 16FF F599 82F8 E5AA 18C6 5220 D9DA D7D4 4EF1 DF08