Re: [PATCH v2] iio: imu: st_lsm6dsx: deselect shub page before reading whoami

[Jonathan Cameron]

On Fri, 3 Jul 2026 14:22:20 +0000
Andreas Kempe <andreas.kempe@xxxxxxxx> wrote:

> Den Thu, Jul 02, 2026 at 06:04:23PM +0100, skrev Jonathan Cameron:
> > On Thu, 2 Jul 2026 14:09:50 +0200
> > Lorenzo Bianconi <lorenzo@xxxxxxxxxx> wrote:
> >   
> > > > As part of driver initialization, e.g. st_lsm6dsx_init_shub() selects
> > > > the shub register page using st_lsm6dsx_set_page(). Selecting the shub
> > > > register page shadows the regular register space so whoami, among other
> > > > registers, is no longer accessible.
> > > >
> > > > In applications where the IMU is permanently powered separately from the
> > > > processor, there is a window where a reset of the CPU leaves the IMU in
> > > > the shub register page. Once this occurs, any subsequent probe attempt
> > > > fails because of the register shadowing.
> > > >
> > > > Using the ism330dlc, the error typically looks like
> > > >
> > > >     st_lsm6dsx_i2c 3-006a: unsupported whoami [10]
> > > >
> > > > with the unknown whoami read from a reserved register in the shub page.
> > > >
> > > > The reset register is also shadowed by the page select, preventing a
> > > > reset from recovering the chip.
> > > >
> > > > Unconditionally clear the shub page before the whoami readout to ensure
> > > > normal register access and allow the initialization to proceed.
> > > >
> > > > Place the fix in st_lsm6dsx_check_whoami() before the whoami check
> > > > because hw->settings, which st_lsm6dsx_set_page() relies on, is first
> > > > assigned in that function.
> > > >
> > > > Placing the fix in a more logical place than the whoami check would
> > > > require a bigger restructuring of the code.
> > > >
> > > > Signed-off-by: Andreas Kempe <andreas.kempe@xxxxxxxx>
> > > > ---
> > > >
> > > >  Changes in v2:
> > > >    - Drop st_lsm6dsx_get_page() and unconditionally clear the shub page.
> > > >    - Make the code comment clearer.
> > > >    - Document the placement rationale in the commit message.
> > > >    - Link to v1: https://lore.kernel.org/linux-iio/20260604132646.1099072-1-andreas.kempe@xxxxxxxx/
> > > >
> > > >  drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c | 21 +++++++++++++++++++-
> > > >  1 file changed, 20 insertions(+), 1 deletion(-)  
> > >
> > > Acked-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
> > >  
> > Given I assume we want to backport this, please send an appropriate
> > Fixes tag in response to this email.
> >   
> 
> Fixes: c91c1c844ebd ("iio: imu: st_lsm6dsx: add i2c embedded controller support")
> 
Thanks,

Applied to the fixes-togreg branch of iio.git and marked for stable.


> > > >
> > > > diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> > > > index 630e2cae6f19..f4edcb73ec8c 100644
> > > > --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> > > > +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> > > > @@ -1712,6 +1712,26 @@ static int st_lsm6dsx_check_whoami(struct st_lsm6dsx_hw *hw, int id,
> > > >             return -ENODEV;
> > > >     }
> > > >
> > > > +   hw->settings = &st_lsm6dsx_sensor_settings[i];
> > > > +
> > > > +   if (hw->settings->shub_settings.page_mux.addr) {
> > > > +           /*
> > > > +            * If the IMU has the shub page selected on init, for example
> > > > +            * after a CPU watchdog reset while the page is selected, the
> > > > +            * regular register space is shadowed. While the regular
> > > > +            * register space is shadowed, the registers needed for
> > > > +            * initializing the IMU are not available.
> > > > +            *
> > > > +            * Unconditionally clear the shub page selection to ensure
> > > > +            * normal register access.
> > > > +            */
> > > > +           err = st_lsm6dsx_set_page(hw, false);
> > > > +           if (err < 0) {
> > > > +                   dev_err(hw->dev, "failed to clear shub page\n");
> > > > +                   return err;
> > > > +           }
> > > > +   }
> > > > +
> > > >     err = regmap_read(hw->regmap, ST_LSM6DSX_REG_WHOAMI_ADDR, &data);
> > > >     if (err < 0) {
> > > >             dev_err(hw->dev, "failed to read whoami register\n");
> > > > @@ -1724,7 +1744,6 @@ static int st_lsm6dsx_check_whoami(struct st_lsm6dsx_hw *hw, int id,
> > > >     }
> > > >
> > > >     *name = st_lsm6dsx_sensor_settings[i].id[j].name;
> > > > -   hw->settings = &st_lsm6dsx_sensor_settings[i];
> > > >
> > > >     return 0;
> > > >  }
> > > > --
> > > > 2.53.0  
> > 
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