Re: RESEND [PATCH v1] iio: potentiometer: mcp4131: fix double application of wiper shift

[Jonathan Cameron]

On Mon, 2 Feb 2026 20:29:20 +0000
Jonathan Cameron <jic23@xxxxxxxxxx> wrote:

> On Mon,  2 Feb 2026 21:15:35 +0100
> Lukas Schmid <lukas.schmid@xxxxxxxxxx> wrote:
> 
> > The MCP4131 wiper address is shifted twice when preparing the SPI
> > command in mcp4131_write_raw().
> > 
> > The address is already shifted when assigned to the local variable
> > "address", but is then shifted again when written to data->buf[0].
> > This results in an incorrect command being sent to the device and
> > breaks wiper writes to the second channel.
> > 
> > Remove the second shift and use the pre-shifted address directly
> > when composing the SPI transfer.
> > 
> > Signed-off-by: Lukas Schmid <lukas.schmid@xxxxxxxxxx>  
> Hi Lukas,
> 
> Good find.  
> Needs a fixes tag though so that we can know how far to backport it.
> looks like this one goes all the way, so I'll just reply here and
> pick this up in a minute once my email reaches lore.
> 
> Fixes: 22d199a53910 ("iio: potentiometer: add driver for Microchip MCP413X/414X/415X/416X/423X/424X/425X/426X")

I picked it up by hand.  A few things to note for next time.
If you do add RESEND then inside the [] so that the tooling maintainers
tend to use to pick stuff up (b4 / git am etc) doesn't included the
RESEND [PATCH v1] in the title of the commit.

Also, if you resend, please include a comment below the --- on why you
did so.

Now applied to my local tree as I'll be rebasing the fixes branch after
the release next weekend and am not planning to do a pull request before
then.

Thanks,

Jonathan

> 
> 
> Thanks,
> 
> Jonathan
> 
> > ---
> >  drivers/iio/potentiometer/mcp4131.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iio/potentiometer/mcp4131.c b/drivers/iio/potentiometer/mcp4131.c
> > index ad082827aad5..56c9111ef5e8 100644
> > --- a/drivers/iio/potentiometer/mcp4131.c
> > +++ b/drivers/iio/potentiometer/mcp4131.c
> > @@ -221,7 +221,7 @@ static int mcp4131_write_raw(struct iio_dev *indio_dev,
> >  
> >  	mutex_lock(&data->lock);
> >  
> > -	data->buf[0] = address << MCP4131_WIPER_SHIFT;
> > +	data->buf[0] = address;
> >  	data->buf[0] |= MCP4131_WRITE | (val >> 8);
> >  	data->buf[1] = val & 0xFF; /* 8 bits here */
> >    
>