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

[Andreas Kempe]

On Fri, Jun 05, 2026 at 01:15:18PM +0100, Jonathan Cameron wrote:
> On Thu, 4 Jun 2026 16:23:27 +0000
> Andreas Kempe <andreas.kempe@xxxxxxxx> wrote:
> > On Thu, Jun 04, 2026 at 06:14:11PM +0200, David Lechner wrote:
> > >
> > > How about setting the SW_RESET bit in the CTRL3_C register during
> > > probe too to ensure the rest of the registers are in a known state?
> > >
> >
> > While the shub register file is selected, the reset register is
> > shadowed so it can't be written without first selecting the normal
> > register file. A reset is already called from probe in
> > st_lsm6dsx_init_device() after the whoami check has passed.
> 
> The fix is fine, but I think it shouldn't be buried in the whoami
> check as it's a bit of a weird side effect.  I'd like a top level
> function that we can see in probe(). That can do the read + write
> if necessary sequence you have in this patch.
> 
> This driver currently hard rejects unknown wai values (which it probably
> should not given fallback compatibles should work). Lets assume that will
> get resolved at somepoint and so the wai gate is advisory only. That
> means that the dance to avoid writing to a device that doesn't match will
> no be useful anyway.
> 
> As such, I'd prefer this 'reset of the register file mux selector' was
> part of the reset function and that was simply called before checking
> WAI.  It fits more logically there than in the whoami check function
> which is just the first place the unexpected setting causes problems.
> That is put it in st_lsm6dsx_reset_device() and call that before
> st_lsm6dsx_check_whoami().  Maybe with a comment to justify that.
> 

I agree fully that its current placement in st_lsm6dsx_check_whoami()
is not optimal.

The reason I put the fix where it is, is because 
st_lsm6dsx_check_whoami() is what assigns hw->settings needed for
st_lsm6dsx_set_page() to work. I moved that assignment to before the
whoami check for that very reason.

As I see it, moving my fix to a more reasonable place would mean a
larger restructuring of the driver or making the whoami check advisory
per your suggestion.

Best regards,
Andreas Kempe