From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5EC59C32793 for ; Wed, 18 Jan 2023 17:18:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230492AbjARRSL (ORCPT ); Wed, 18 Jan 2023 12:18:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47880 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230495AbjARRSE (ORCPT ); Wed, 18 Jan 2023 12:18:04 -0500 Received: from relay9-d.mail.gandi.net (relay9-d.mail.gandi.net [217.70.183.199]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8D80D51C41; Wed, 18 Jan 2023 09:18:01 -0800 (PST) Received: from booty (unknown [77.244.183.192]) (Authenticated sender: luca.ceresoli@bootlin.com) by mail.gandi.net (Postfix) with ESMTPSA id 867E7FF803; Wed, 18 Jan 2023 17:17:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1674062279; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=HHiWQiQKmF9Aq364tQ1OQoYyXwqW/hpH1Vz8i01CmX4=; b=W2GeEJNXWZ+yf3j1rPF8scQWxjgLiyhA2BCQpdJJj7AFFTLb/MgCZIUAiUqETbp8WtS0CS 0rPiblgQSwSGIwccSso7YA1KfnnxvlsOY413u0TdNHcb09xaZyKPpciZDkD2Am5/CskueT GSTiH080p3ycDeogzaEXQ1oTxt+QLSIQQ61z1SJSIhQRzX0YPe8ucIMNzCut/UZQObmOzm Rkk+cBP9wKmvoHpi1PyiQOgo0U0CDCY9vavR3Iszjfjl1flEHy/L79ojuljCxDcF3/UJCn 3QOfS56cFNigVaELWtoRE9ubBIj4bmwcG9AclRZGVqgd01zcvEJiNdpbnSkwsQ== Date: Wed, 18 Jan 2023 18:17:53 +0100 From: Luca Ceresoli To: Andy Shevchenko Cc: Tomi Valkeinen , linux-media@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-i2c@vger.kernel.org, Rob Herring , Krzysztof Kozlowski , Wolfram Sang , Matti Vaittinen , Laurent Pinchart , Mauro Carvalho Chehab , Peter Rosin , Liam Girdwood , Mark Brown , Sakari Ailus , Michael Tretter , Shawn Tu , Hans Verkuil , Mike Pagano , Krzysztof =?UTF-8?Q?Ha=C5=82asa?= , Marek Vasut , Luca Ceresoli Subject: Re: [PATCH v7 1/7] i2c: add I2C Address Translator (ATR) support Message-ID: <20230118181753.7a325953@booty> In-Reply-To: References: <20230118124031.788940-1-tomi.valkeinen@ideasonboard.com> <20230118124031.788940-2-tomi.valkeinen@ideasonboard.com> Organization: Bootlin X-Mailer: Claws Mail 4.0.0 (GTK+ 3.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org Hello Andy, On Wed, 18 Jan 2023 16:23:53 +0200 Andy Shevchenko wrote: > On Wed, Jan 18, 2023 at 02:40:25PM +0200, Tomi Valkeinen wrote: > > From: Luca Ceresoli > > > > An ATR is a device that looks similar to an i2c-mux: it has an I2C > > slave "upstream" port and N master "downstream" ports, and forwards > > transactions from upstream to the appropriate downstream port. But is > > is different in that the forwarded transaction has a different slave > > is is ? > > > address. The address used on the upstream bus is called the "alias" > > and is (potentially) different from the physical slave address of the > > downstream chip. > > > > Add a helper file (just like i2c-mux.c for a mux or switch) to allow > > implementing ATR features in a device driver. The helper takes care or > > adapter creation/destruction and translates addresses at each transaction. > > ... > > > +A typical example follows. > > + > > +Topology:: > > + > > + Slave X @ 0x10 > > + .-----. | > > + .-----. | |---+---- B > > + | CPU |--A--| ATR | > > + `-----' | |---+---- C > > + `-----' | > > + Slave Y @ 0x10 > > + > > +Alias table: > > + > > +.. table:: > > + > > + ====== ===== > > + Client Alias > > + ====== ===== > > + X 0x20 > > + Y 0x30 > > + ====== ===== > > + > > +Transaction: > > + > > + - Slave X driver sends a transaction (on adapter B), slave address 0x10 > > + - ATR driver rewrites messages with address 0x20, forwards to adapter A > > + - Physical I2C transaction on bus A, slave address 0x20 > > + - ATR chip propagates transaction on bus B with address translated to 0x10 > > + - Slave X chip replies on bus B > > + - ATR chip forwards reply on bus A > > + - ATR driver rewrites messages with address 0x10 > > + - Slave X driver gets back the msgs[], with reply and address 0x10 > > I'm not sure I got the real / virtual status of the adapters. Are the B and C > virtual ones, while A is the real? Let me reply, as I wrote these docs back at the times and thus I feel guilty in case that's unclear. :) I don't like the word "virtual" in this situation. A, B and C are all physical busses, made of copper and run by electrons on PCBs. B and C are the "remote" or "downstream" busses (w.r.t. the CPU), where the i2c devices are and where transactions happen using the address that the chip responds to. A is the "local" or "upstream" bus that is driven directly by the CPU (*) and where address aliases are used. Using aliases there is necessary because using address 0x10 would be ambiguous as there are two 0x10 chips out there. (*) There could be more layers of course, but still A is "closer to the CPU than B and C", for the sake of completeness. ... > > +void i2c_atr_set_driver_data(struct i2c_atr *atr, void *data) > > +{ > > + atr->priv = data; > > +} > > +EXPORT_SYMBOL_NS_GPL(i2c_atr_set_driver_data, I2C_ATR); > > + > > +void *i2c_atr_get_driver_data(struct i2c_atr *atr) > > +{ > > + return atr->priv; > > +} > > +EXPORT_SYMBOL_NS_GPL(i2c_atr_get_driver_data, I2C_ATR); > > Just to be sure: Is it really _driver_ data and not _device instance_ data? It is device instance data indeed. I don't remember why this got changed, but in v3 it was i2c_atr_set_clientdata(). [v3] https://lore.kernel.org/all/20220206115939.3091265-3-luca@lucaceresoli.net/ -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com