From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jean Delvare Subject: Re: [PATCH] pca954x: Initialize the mux to disconnected state in pca954x_probe() Date: Sat, 18 Jun 2011 10:47:32 +0200 Message-ID: <20110618104732.62a19129@endymion.delvare> References: <20110618005949.2F442E0866@hockey.mtv.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20110618005949.2F442E0866-z1f3I2EsBvXHt/MElyovVYaSKrA+ACpX0E9HWUfgJXw@public.gmane.org> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Petri Gynther Cc: Rodolfo Giometti , Kumar Gala , linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-i2c@vger.kernel.org On Fri, 17 Jun 2011 18:00:00 -0700, Petri Gynther wrote: > 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 > --- > drivers/i2c/muxes/pca954x.c | 7 ++++--- > 1 files changed, 4 insertions(+), 3 deletions(-) > > diff --git a/drivers/i2c/muxes/pca954x.c b/drivers/i2c/muxes/pca954x.c > index 54e1ce7..6f89536 100644 > --- a/drivers/i2c/muxes/pca954x.c > +++ b/drivers/i2c/muxes/pca954x.c > @@ -201,10 +201,11 @@ static int pca954x_probe(struct i2c_client *client, > > 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; > } Good fix, applied, thanks. -- Jean Delvare