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authorPetri Gynther <pgynther@google.com>2011-06-29 11:36:11 +0200
committerJean Delvare <khali@endymion.delvare>2011-06-29 11:36:11 +0200
commitcd823db8b1161ef0d756514d280715a576d65cc3 (patch)
tree96eb9acd38c9206be203219023df5bde4700ce88 /drivers/i2c/muxes
parent9b640f2e154268cb516efcaf9c434f2e73c6783e (diff)
i2c/pca954x: Initialize the mux to disconnected state
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@google.com> Signed-off-by: Jean Delvare <khali@linux-fr.org> Cc: stable@kernel.org
Diffstat (limited to 'drivers/i2c/muxes')
-rw-r--r--drivers/i2c/muxes/pca954x.c7
1 files changed, 4 insertions, 3 deletions
diff --git a/drivers/i2c/muxes/pca954x.c b/drivers/i2c/muxes/pca954x.c
index 54e1ce73534..6f895366463 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;
}