From patchwork Sun Apr 6 11:49:32 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wolfram Sang X-Patchwork-Id: 337258 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id E0B3B1400E1 for ; Sun, 6 Apr 2014 21:49:46 +1000 (EST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754219AbaDFLtp (ORCPT ); Sun, 6 Apr 2014 07:49:45 -0400 Received: from sauhun.de ([89.238.76.85]:51919 "EHLO pokefinder.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753799AbaDFLtp (ORCPT ); Sun, 6 Apr 2014 07:49:45 -0400 Received: from frbg-5d84f8b2.pool.mediaways.net ([93.132.248.178]:40710 helo=localhost) by pokefinder.org with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.69) (envelope-from ) id 1WWla3-0006IA-II; Sun, 06 Apr 2014 13:49:43 +0200 From: Wolfram Sang To: linux-i2c@vger.kernel.org Cc: Wolfram Sang Subject: [PATCH] Documentation: i2c: improve section about flags mangling the protocol Date: Sun, 6 Apr 2014 13:49:32 +0200 Message-Id: <1396784972-3965-1-git-send-email-wsa@the-dreams.de> X-Mailer: git-send-email 1.9.1 Sender: linux-i2c-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org Sort the entries alphabetically. Make the introductory paragraph more precise. Skip useless 'Flag' introduction from the entries. Remove trailing white spaces from the file. Add missing I2C_M_STOP entry. Signed-off-by: Wolfram Sang --- Documentation/i2c/i2c-protocol | 35 ++++++++++++++++++++--------------- 1 file changed, 20 insertions(+), 15 deletions(-) diff --git a/Documentation/i2c/i2c-protocol b/Documentation/i2c/i2c-protocol index 0b3e62d1f77a..ff6d6cee6c7e 100644 --- a/Documentation/i2c/i2c-protocol +++ b/Documentation/i2c/i2c-protocol @@ -6,8 +6,8 @@ Key to symbols S (1 bit) : Start bit P (1 bit) : Stop bit Rd/Wr (1 bit) : Read/Write bit. Rd equals 1, Wr equals 0. -A, NA (1 bit) : Accept and reverse accept bit. -Addr (7 bits): I2C 7 bit address. Note that this can be expanded as usual to +A, NA (1 bit) : Accept and reverse accept bit. +Addr (7 bits): I2C 7 bit address. Note that this can be expanded as usual to get a 10 bit I2C address. Comm (8 bits): Command byte, a data byte which often selects a register on the device. @@ -49,11 +49,20 @@ a byte read, followed by a byte write: Modified transactions ===================== -The following modifications to the I2C protocol can also be generated, -with the exception of I2C_M_NOSTART these are usually only needed to -work around device issues: +The following modifications to the I2C protocol can also be generated by +setting these flags for i2c messages. With the exception of I2C_M_NOSTART, they +are usually only needed to work around device issues: - Flag I2C_M_NOSTART: +I2C_M_IGNORE_NAK: + Normally message is interrupted immediately if there is [NA] from the + client. Setting this flag treats any [NA] as [A], and all of + message is sent. + These messages may still fail to SCL lo->hi timeout. + +I2C_M_NO_RD_ACK: + In a read message, master A/NA bit is skipped. + +I2C_M_NOSTART: In a combined transaction, no 'S Addr Wr/Rd [A]' is generated at some point. For example, setting I2C_M_NOSTART on the second partial message generates something like: @@ -67,17 +76,13 @@ work around device issues: I2C device but may also be used between direction changes by some rare devices. - Flags I2C_M_REV_DIR_ADDR +I2C_M_REV_DIR_ADDR: This toggles the Rd/Wr flag. That is, if you want to do a write, but need to emit an Rd instead of a Wr, or vice versa, you set this flag. For example: S Addr Rd [A] Data [A] Data [A] ... [A] Data [A] P - Flags I2C_M_IGNORE_NAK - Normally message is interrupted immediately if there is [NA] from the - client. Setting this flag treats any [NA] as [A], and all of - message is sent. - These messages may still fail to SCL lo->hi timeout. - - Flags I2C_M_NO_RD_ACK - In a read message, master A/NA bit is skipped. +I2C_M_STOP: + Force a stop condition (P) after the message. Some I2C related protocols + like SCCB require that. Normally, you really don't want to get interrupted + between the messages of one transfer.