Re: [PATCH 6/8] iio: dac: ad3552r-hs: exit for error on wrong chip id

[Conor Dooley <conor@kernel.org>]

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On Thu, Dec 19, 2024 at 04:54:46PM +0000, Jonathan Cameron wrote:
> On Mon, 16 Dec 2024 21:36:26 +0100
> Angelo Dureghello <adureghello@baylibre.com> wrote:
> 
> > From: Angelo Dureghello <adureghello@baylibre.com>
> > 
> > Exit for error on wrong chip id, otherwise driver continues
> > with wrong assumptions.
> Why? Chip ID does not define all future compatible parts, just the
> ones we know about today.
> 
> The reason not failing is that the moment we do exit on a mismatch
> we can never support fallback device tree compatible IDs.  Is there
> no chance that ADI will release a backwards compatible part in the
> future that we'd like to work with old kernels?
> 
> Any mismatch in DT vs hardware present is considered a firmware
> bug, not a kernel problem.
> We used to reject missmatched IDs but after a long discussion with
> DT maintainers it became clear that broke their model.

I'd probably still say the warning of the info message is still too
harsh, and that it should be something like "Chip ID mismatch, operating
detected 0x%x as a 0x%x" ;)

> Thanks,
> 
> Jonathan
> 
> > 
> > Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
> > ---
> >  drivers/iio/dac/ad3552r-hs.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/iio/dac/ad3552r-hs.c b/drivers/iio/dac/ad3552r-hs.c
> > index 8974df625670..e613eee7fc11 100644
> > --- a/drivers/iio/dac/ad3552r-hs.c
> > +++ b/drivers/iio/dac/ad3552r-hs.c
> > @@ -326,8 +326,9 @@ static int ad3552r_hs_setup(struct ad3552r_hs_state *st)
> >  
> >  	id |= val << 8;
> >  	if (id != st->model_data->chip_id)
> > -		dev_info(st->dev, "Chip ID error. Expected 0x%x, Read 0x%x\n",
> > -			 AD3552R_ID, id);
> > +		return dev_err_probe(st->dev, -ENODEV,
> > +				     "chip id error, expected 0x%x, got 0x%x\n",
> > +				     st->model_data->chip_id, id);
> >  
> >  	/* Clear reset error flag, see ad3552r manual, rev B table 38. */
> >  	ret = st->data->bus_reg_write(st->back, AD3552R_REG_ADDR_ERR_STATUS,
> > 
> 

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