On Fri, 17 Jun 2011 18:00:00 -0700, Petri Gynther wrote:
> 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>
> ---
> 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;
> }
Good fix, applied, thanks.
--
Jean Delvare
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