This is a note to let you know that I've just added the patch titled
i2c/pca954x: Initialize the mux to disconnected state
to the 2.6.39-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
i2c-pca954x-initialize-the-mux-to-disconnected-state.patch
and it can be found in the queue-2.6.39 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From cd823db8b1161ef0d756514d280715a576d65cc3 Mon Sep 17 00:00:00 2001
From: Petri Gynther <[email protected]>
Date: Wed, 29 Jun 2011 11:36:11 +0200
Subject: i2c/pca954x: Initialize the mux to disconnected state
From: Petri Gynther <[email protected]>
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 <[email protected]>
Signed-off-by: Jean Delvare <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
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;
}
Patches currently in stable-queue which might be from [email protected] are
queue-2.6.39/i2c-pca954x-initialize-the-mux-to-disconnected-state.patch
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