From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maxime Ripard Subject: Re: [PATCH v2 1/4] i2c: sunxi: Add Reduced Serial Bus (RSB) support Date: Thu, 5 Mar 2015 19:28:17 +0100 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> Reply-To: linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="MHoG8na4IvP3G3ze" Return-path: Content-Disposition: inline In-Reply-To: <20150304172710.GA884@katana> List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , To: Wolfram Sang Cc: Chen-Yu Tsai , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org, Hans de Goede , Arnd Bergmann List-Id: devicetree@vger.kernel.org --MHoG8na4IvP3G3ze Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline 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 byte > > 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 this. > > > > 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 > > > > 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/Pull > > 2 Wire Interface) controller support"). > > > > Signed-off-by: Chen-Yu Tsai > > 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 -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com --MHoG8na4IvP3G3ze--