Re: [PATCH] iio: temperature: mlx90614: Fix dual channel probe condition check

[Salah Triki <salah.triki@gmail.com>]

Hi Crt,

Thanks for your feedback.

Actually, the patch primarily fixes the behavior for the MLX90614.

In the current codebase, MLX90614 has `chip_info->dual_channel = true`.
Because `mlx90614_probe_num_ir_sensors()` checks
`if (chip_info->dual_channel)`, it returns 0 immediately for MLX90614
without reading the EEPROM CONFIG1 register. As a result, dual-channel
MLX90614 sensors are incorrectly registered as single-channel devices.

For MLX90615 (`dual_channel = false`), the condition was bypassed, causing
an unnecessary SMBus read to EEPROM CONFIG1, even though MLX90615 only
supports a single object channel.

By changing the check to `if (!chip_info->dual_channel)`, we fix both
issues:
1. MLX90614 correctly reads EEPROM CONFIG1 to detect whether it operates
in single or dual channel mode.
2. MLX90615 skips the EEPROM read entirely.

I don't have physical hardware to test this on; this bug was spotted via
code inspection.

Best regards,
Salah

On Thu, Sep 17, 2026 at 01:27:48PM +0200, Crt Mori wrote:
> So this fix is for the MLX90615, which is registered as single channel
> operation? Did you test on 90614 as well?
> 
> Best regards,
> Crt
> 
> Crt Mori
> 
> Melexis Technologies NV
> Transportstraat 1
> 3980 Tessenderlo
> 
> Mobile: +32 492 46 22 15
> E-mail: cmo@melexis.com
> Website: www.melexis.com
> 
> ----------------------------------------------------------
> The contents of this e-mail are CONFIDENTIAL AND PROPRIETARY. Please
> read our disclaimer at http://www.melexis.com/mailpolicy
> 
> 
> On Thu, 17 Sept 2026 at 13:01, Salah Triki <salah.triki@gmail.com> wrote:
> >
> > In mlx90614_probe_num_ir_sensors(), the check on chip_info->dual_channel
> > is inverted.
> >
> > Currently, if dual_channel is true (MLX90614), the function returns 0
> > immediately without checking op_eeprom_config1. This forces all MLX90614
> > devices to be registered as single sensor (num_channels = 2), making the
> > second object temperature channel inaccessible.
> >
> > Conversely, if dual_channel is false (MLX90615), the function skips the
> > early return and performs an unnecessary SMBus read on EEPROM CONFIG1 even
> > though MLX90615 does not support dual channel operation.
> >
> > Fix this by negating the condition so that single-channel chips return
> > early with 0, while dual-channel capable chips (MLX90614) proceed to read
> > the EEPROM configuration register to detect whether 1 or 2 object channels
> > are present.
> >
> > Fixes: 3d5ead238bc8 ("iio: mlx90614: Factor our register IO and constants into model specific descriptor")
> > Assisted-by: LLM
> > Signed-off-by: Salah Triki <salah.triki@gmail.com>
> > ---
> >  drivers/iio/temperature/mlx90614.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/iio/temperature/mlx90614.c b/drivers/iio/temperature/mlx90614.c
> > index 27d6ab5f5d7a..4f79da1f905e 100644
> > --- a/drivers/iio/temperature/mlx90614.c
> > +++ b/drivers/iio/temperature/mlx90614.c
> > @@ -565,7 +565,7 @@ static int mlx90614_probe_num_ir_sensors(struct i2c_client *client)
> >         const struct mlx_chip_info *chip_info = data->chip_info;
> >         s32 ret;
> >
> > -       if (chip_info->dual_channel)
> > +       if (!chip_info->dual_channel)
> >                 return 0;
> >
> >         ret = i2c_smbus_read_word_data(client, chip_info->op_eeprom_config1);
> > --
> > 2.43.0
> >