From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754815Ab1GHFFI (ORCPT ); Fri, 8 Jul 2011 01:05:08 -0400 Received: from cantor2.suse.de ([195.135.220.15]:42457 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755049Ab1GHFFF (ORCPT ); Fri, 8 Jul 2011 01:05:05 -0400 X-Mailbox-Line: From gregkh@clark.kroah.org Thu Jul 7 17:17:01 2011 Message-Id: <20110708001700.927287231@clark.kroah.org> User-Agent: quilt/0.48-16.4 Date: Thu, 07 Jul 2011 17:16:56 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Petri Gynther , Jean Delvare Subject: [084/107] i2c/pca954x: Initialize the mux to disconnected state In-Reply-To: <20110708001740.GA14031@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.39-stable review patch. If anyone has any objections, please let us know. ------------------ From: Petri Gynther commit cd823db8b1161ef0d756514d280715a576d65cc3 upstream. pca954x power-on default is channel 0 connected. If multiple pca954x muxes are connected to the same physical I2C bus, the parent bus will see channel 0 devices behind both muxes by default. This is bad. Scenario: -- pca954x @ 0x70 -- ch 0 (I2C-bus-101) -- EEPROM @ 0x50 | I2C-bus-1 --- | -- pca954x @ 0x71 -- ch 0 (I2C-bus-111) -- EEPROM @ 0x50 1. Load I2C bus driver: creates I2C-bus-1 2. Load pca954x driver: creates virtual I2C-bus-101 and I2C-bus-111 3. Load eeprom driver 4. Try to read EEPROM @ 0x50 on I2C-bus-101. The transaction will also bleed onto I2C-bus-111 because pca954x @ 0x71 channel 0 is connected by default. Fix: Initialize pca954x to disconnected state in pca954x_probe() Signed-off-by: Petri Gynther Signed-off-by: Jean Delvare Signed-off-by: Greg Kroah-Hartman --- drivers/i2c/muxes/pca954x.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) --- a/drivers/i2c/muxes/pca954x.c +++ b/drivers/i2c/muxes/pca954x.c @@ -201,10 +201,11 @@ static int pca954x_probe(struct i2c_clie i2c_set_clientdata(client, data); - /* Read the mux register at addr to verify - * that the mux is in fact present. + /* Write the mux register at addr to verify + * that the mux is in fact present. This also + * initializes the mux to disconnected state. */ - if (i2c_smbus_read_byte(client) < 0) { + if (i2c_smbus_write_byte(client, 0) < 0) { dev_warn(&client->dev, "probe failed\n"); goto exit_free; }