diff options
| author | Petri Gynther <pgynther@google.com> | 2011-06-29 09:36:11 (GMT) |
|---|---|---|
| committer | Jean Delvare <khali@endymion.delvare> | 2011-06-29 09:36:11 (GMT) |
| commit | cd823db8b1161ef0d756514d280715a576d65cc3 (patch) | |
| tree | 96eb9acd38c9206be203219023df5bde4700ce88 | |
| parent | 9b640f2e154268cb516efcaf9c434f2e73c6783e (diff) | |
| download | linux-cd823db8b1161ef0d756514d280715a576d65cc3.tar.xz | |
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
| -rw-r--r-- | 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; } |