linux-kernel - [084/107] i2c/pca954x: Initialize the mux to disconnected state

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Date:	Thu, 07 Jul 2011 17:16:56 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Petri Gynther <pgynther@...gle.com>,
	Jean Delvare <khali@...ux-fr.org>
Subject: [084/107] i2c/pca954x: Initialize the mux to disconnected state

2.6.39-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Petri Gynther <pgynther@...gle.com>

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 <pgynther@...gle.com>
Signed-off-by: Jean Delvare <khali@...ux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 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;
 	}


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