From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755168Ab3AXLNz (ORCPT ); Thu, 24 Jan 2013 06:13:55 -0500 Received: from metis.ext.pengutronix.de ([92.198.50.35]:49192 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753804Ab3AXLNj (ORCPT ); Thu, 24 Jan 2013 06:13:39 -0500 Date: Thu, 24 Jan 2013 12:13:29 +0100 From: Wolfram Sang To: Mark Brown Cc: Stephen Warren , Naveen Krishna Chatradhi , linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org, grundler@chromium.org, devicetree-discuss@lists.ozlabs.org, ben-linux@fluff.org, khali@linux-fr.org, naveen@chromium.org Subject: Re: [PATCH 1/2] i2c-core: Add gpio based bus arbitration implementation Message-ID: <20130124111329.GC12933@pengutronix.de> References: <1355464254-12768-1-git-send-email-ch.naveen@samsung.com> <1355464254-12768-2-git-send-email-ch.naveen@samsung.com> <50CB4E99.9060506@wwwdotorg.org> <20121215142135.GB22033@opensource.wolfsonmicro.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="6zdv2QT/q3FMhpsV" Content-Disposition: inline In-Reply-To: <20121215142135.GB22033@opensource.wolfsonmicro.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-SA-Exim-Connect-IP: 2001:6f8:1178:2:21e:67ff:fe11:9c5c X-SA-Exim-Mail-From: wsa@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --6zdv2QT/q3FMhpsV Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi, On Sat, Dec 15, 2012 at 11:21:36PM +0900, Mark Brown wrote: > On Fri, Dec 14, 2012 at 09:06:49AM -0700, Stephen Warren wrote: > > On 12/13/2012 10:50 PM, Naveen Krishna Chatradhi wrote: >=20 > > > +The first should be an output, and is used to claim the I2C bus, > > > +the second should be an input, and signals that the other side (Clie= nt) > > > +wants to claim the bus. This allows two masters to share the same I2= C bus. >=20 > > I'm confused why this is even needed; the I2C protocol itself defines > > how multi-master is supposed to work, just using the regular SCL/SDA li= nes. >=20 > Practically speaking essentially no systems actually do that - mostly > Linux will treat failure to get the bus as an error for example. It is true that Linux currently does not have proper multi-master support. It is worth a look what is missing and how far we can get with the I2C specified arbitration IMO. > also get things like read operations which appear as multiple > transactions on the I2C bus so require something higher level than what > multi-master provides. I don't get what you mean here. Can you elaborate? That being said. Grant's design was the most promising one. Thanks, Wolfram --=20 Pengutronix e.K. | Wolfram Sang | Industrial Linux Solutions | http://www.pengutronix.de/ | --6zdv2QT/q3FMhpsV Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iEYEARECAAYFAlEBF1kACgkQD27XaX1/VRullQCePgYzSfFOMBAK94oXjHZnLFtt TYIAoMQogd0XfDbXQpVnMGySY0AW5KEI =Zzsm -----END PGP SIGNATURE----- --6zdv2QT/q3FMhpsV--