Re: [PATCH v4 1/2] iio: light: cm3323: fix reg_conf not being initialized correctly

On Tue,  7 Apr 2026 17:17:01 +0200
Aldo Conte <[email protected]> wrote:

> The code stores the return value of i2c_smbus_write_word_data()
> in data->reg_conf; however, this value represents the result
> of the write operation and not the value actually written to
> the configuration register. This meant that the contents of
> data->reg_conf did not truly reflect the contents
> of the hardware register.
> 
> Instead, save the value of the register before the write
> and use this value in the I2C write.
> 
> The bug was found by code inspection: i2c_smbus_write_word_data()
> returns 0 on success, not the value written to the register.
> 
> Tested using i2c-stub on a Raspberry Pi 3B running a custom 6.19.10
> kernel. Before loading the driver, the configuration register 0x00
> CM3323_CMD_CONF was populated with 0x0030 using
> `i2cset -y 11 0x10 0x00 0x0030 w`, encoding an integration time of 320ms
> in bits[6:4].
> 
> Due to incorrect initialization of data->reg_conf in
> cm3323_init(), the print of integration_time returns 0.040000
> instead of the expected 0.320000. This happens because the read of the
> integration_time depends on cm3323_get_it_bits() that is based on the
> value of data->reg_conf, which is erroneously set to 0.
> 
> With this fix applied, data->reg_conf correctly saves 0x0030 after init
> and the successive integration_time reports 0.320000 as expected.
> 
> Fixes: 8b0544263761 ("iio: light: Add support for Capella CM3323 color sensor")
> Cc: [email protected]
> Signed-off-by: Aldo Conte <[email protected]>
Applied this patch, but patch 2 will need to wait for this to make its way
into upstream - probably middle of the next cycle before that is in place.

thanks,

Jonathan

> ---
>  drivers/iio/light/cm3323.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/light/cm3323.c b/drivers/iio/light/cm3323.c
> index 79ad6e2209ca..0fe61b8a7029 100644
> --- a/drivers/iio/light/cm3323.c
> +++ b/drivers/iio/light/cm3323.c
> @@ -89,15 +89,14 @@ static int cm3323_init(struct iio_dev *indio_dev)
>  
>  	/* enable sensor and set auto force mode */
>  	ret &= ~(CM3323_CONF_SD_BIT | CM3323_CONF_AF_BIT);
> +	data->reg_conf = ret;
>  
> -	ret = i2c_smbus_write_word_data(data->client, CM3323_CMD_CONF, ret);
> +	ret = i2c_smbus_write_word_data(data->client, CM3323_CMD_CONF, data->reg_conf);
>  	if (ret < 0) {
>  		dev_err(&data->client->dev, "Error writing reg_conf\n");
>  		return ret;
>  	}
>  
> -	data->reg_conf = ret;
> -
>  	return 0;
>  }
>