Port of a Linux kernel commit cd823db8b1161ef0d756514d280715a576d65cc3
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@xxxxxxxxxx>
Signed-off-by: Jean Delvare <khali@xxxxxxxxxxxx>
Cc: stable@xxxxxxxxxx
Signed-off-by: Andrey Smirnov <andrew.smirnov@xxxxxxxxx>
---
drivers/i2c/muxes/i2c-mux-pca954x.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index bbc4870c3e..b820be0847 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -195,10 +195,11 @@ static int pca954x_probe(struct device_d *dev)
if (gpio_is_valid(gpio))
gpio_direction_output(gpio, 1);
- /* Read the mux register at addr to verify
- * that the mux is in fact present.
- */
- if (i2c_smbus_read_byte(client) < 0) {
+ /* 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_write_byte(client, 0) < 0) {
dev_warn(&client->dev, "probe failed\n");
goto exit_free;
}
--
2.21.0
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