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

[Lukas Schmid <lukas.schmid@netcube.li>]

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On Montag, 2. Februar 2026 21:34:43 Mitteleuropäische Normalzeit Jonathan 
Cameron wrote:
> On Mon, 2 Feb 2026 20:29:20 +0000
> 
> Jonathan Cameron <jic23@kernel.org> wrote:
> > On Mon,  2 Feb 2026 21:15:35 +0100
> > 
> > Lukas Schmid <lukas.schmid@netcube.li> 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@netcube.li>
> > 
> > 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.
> 
Hi Jonathan,

thank you for your hints. Will make sure to follow them next time.

Best regards,
Lukas

> 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 */


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