From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755901AbbCESaH (ORCPT ); Thu, 5 Mar 2015 13:30:07 -0500 Received: from down.free-electrons.com ([37.187.137.238]:60224 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751565AbbCESaE (ORCPT ); Thu, 5 Mar 2015 13:30:04 -0500 Date: Thu, 5 Mar 2015 19:28:17 +0100 From: Maxime Ripard To: Wolfram Sang Cc: Chen-Yu Tsai , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-sunxi@googlegroups.com, Hans de Goede , Arnd Bergmann Subject: Re: [PATCH v2 1/4] i2c: sunxi: Add Reduced Serial Bus (RSB) support Message-ID: <20150305182817.GB4911@lukather> References: <1425284686-5116-1-git-send-email-wens@csie.org> <1425284686-5116-2-git-send-email-wens@csie.org> <20150304172710.GA884@katana> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="MHoG8na4IvP3G3ze" Content-Disposition: inline In-Reply-To: <20150304172710.GA884@katana> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --MHoG8na4IvP3G3ze Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi Wolfram, On Wed, Mar 04, 2015 at 06:27:11PM +0100, Wolfram Sang wrote: > On Mon, Mar 02, 2015 at 04:24:43PM +0800, Chen-Yu Tsai wrote: > > The RSB controller looks like an SMBus controller which only supports b= yte > > and word data transfers. It can also do double-word data transfers, but= the > > I2C subsystem does not support this, nor have we seen devices using thi= s. > >=20 > > The RSB differs from standard SMBus protocol on several aspects: > > - it uses addresses set at runtime to address slaves. Runtime addresses > > are sent to slaves using their 12bit hardware addresses. Up to 15 > > runtime addresses are available. > > - it adds a parity bit every 8bits of data and address for read and > > write accesses; this replaces the ack bit > > - only one read access is required to read a byte (instead of a write > > followed by a read access in standard SMBus protocol) > > - there's no Ack bit after each read access > >=20 > > This means this bus cannot be used to interface with standard SMBus > > devices (known devices supporting this interface are the AXP223, AXP806, > > AXP809 PMICs and the AC100 codec/RTC). However the RSB protocol is an > > extension of P2WI, which was close enough to SMBus to be integrated into > > the I2C subsystem in commit 3e833490fae5 ("i2c: sunxi: add P2WI (Push/P= ull > > 2 Wire Interface) controller support"). > >=20 > > Signed-off-by: Chen-Yu Tsai >=20 > I don't have the bandwidth for a full review right now. However, I > already wanted to tell you guys that my gut feeling is that this > protocol is quite far away from I2C. P2WI was already at the edge. > Maybe there is a better place for such custom stuff? I dunno yet. That's unfortunate, especially since it looks closer to SPI than what P2WI even was. What would be your suggestion? Thanks, Maxime --=20 Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com --MHoG8na4IvP3G3ze Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJU+KBAAAoJEBx+YmzsjxAg9joP/3bUCJiwuVIlS3ppRRnQq2jx UUD+96P41igyxSQuE739TIjawdTMgUn1EiewPSB2g8QnC2Rmv8Opd1auQ8SJSR2f fkQ6swIx9fMI+8TgZRmGlJ8i5tSUbcoBr4pf3kwQHrC5M30gsQVcgdmLyVkf1Mkp mLlpN+VIZZ0H0EWrMWytt98/EUBUoA0nB3wEzoZgbkWzgzB1tXfjBaHAHZKV3GRN Iw8DJcHL2tLdAynFaY+tMtrA8Ueav7ViVODnQxrizYRWzkAmiYpoy6yhAvJItlHA 64fUfBZY5ndoyfFLhykwER+KdxVI3tj+CKf/fjuNHvKp1nw1HudGqbG8K8bmEUtR RYFPODkJGFGrbQOpE6JQF1WZRLl2KdAfFOgx8XPgzjC+fmR4KdLk7UNiJtY+6Am1 lejwaHVr4UbY+szbUQis4wKtRAKa/PbC3qWO2b4ZqdxGCdXHcMKZpo+Zq1sw+oQk 51Wq9esKrwM5o3iNY9wh0LisXpB3+bwhDutYQZKv/hOfPQ7+/uq2Ozpa6SqTdU2g CnSLsr47tjujo1U5Vki1K6VDWNgGeZGNCjr2ywih0XyxeMKkoXGiUAjwhkFGhwtV 5hCt13UqyW6GELcI6AZ4OgPZPfIT4Kq9ScKgE1Dm8EgwNVQ0e/qBdyUv03kQlZ3o SZlzvqdPHNbt7tXW4BK+ =ucjB -----END PGP SIGNATURE----- --MHoG8na4IvP3G3ze--