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

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Message-ID: <20241219165446.7b8d0a9a@jic23-huawei>
Date: Thu, 19 Dec 2024 16:54:46 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Angelo Dureghello <adureghello@...libre.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich
 <Michael.Hennerich@...log.com>, Mihail Chindris
 <mihail.chindris@...log.com>, Nuno Sa <nuno.sa@...log.com>, David Lechner
 <dlechner@...libre.com>, Olivier Moysan <olivier.moysan@...s.st.com>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/8] iio: dac: ad3552r-hs: exit for error on wrong chip
 id

On Mon, 16 Dec 2024 21:36:26 +0100
Angelo Dureghello <adureghello@...libre.com> wrote:

> From: Angelo Dureghello <adureghello@...libre.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.

Thanks,

Jonathan

> 
> Signed-off-by: Angelo Dureghello <adureghello@...libre.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,
>