linux-kernel - Re: [PATCH 2/2] iio: adc: ad9467: make iio backend optional

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Message-ID: <e095bc11-9986-40bb-8ad2-967ee85f67e9@vaisala.com>
Date: Fri, 19 Dec 2025 13:16:57 +0200
From: Tomas Melin <tomas.melin@...sala.com>
To: Nuno Sá <noname.nuno@...il.com>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Nuno Sa <nuno.sa@...log.com>, Lars-Peter Clausen <lars@...afoo.de>,
 Jonathan Cameron <jic23@...nel.org>, David Lechner <dlechner@...libre.com>,
 Andy Shevchenko <andy@...nel.org>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] iio: adc: ad9467: make iio backend optional


On 18/12/2025 15:49, Nuno Sá wrote:
> On Tue, 2025-12-16 at 11:40 +0000, Tomas Melin wrote:
>> Not all users can or want to use the device with an iio-backend.
>> For these users, let the driver work in standalone mode, not coupled
>> to the backend or the services it provides.
>>
>> Signed-off-by: Tomas Melin <tomas.melin@...sala.com>
>> ---
>>  drivers/iio/adc/ad9467.c | 37 +++++++++++++++++++++++++------------
>>  1 file changed, 25 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/iio/adc/ad9467.c b/drivers/iio/adc/ad9467.c
>> index 60fc3361b2689a4c38287c613ef93fe00338e5fa..37b8f88da6681d44f3fbbb6c8c171ae7117b9090 100644
>> --- a/drivers/iio/adc/ad9467.c
>> +++ b/drivers/iio/adc/ad9467.c
>> @@ -1000,6 +1000,9 @@ static int ad9467_update_scan_mode(struct iio_dev *indio_dev,
>>  	unsigned int c;
>>  	int ret;
>>  
>> +	if (!st->back)
>> +		return -EOPNOTSUPP;
>> +
> 
> Let's not add the buffering interface if we can't control it.
> Having it just to return error does not make sense to me. This means yet another info:
> 
> https://elixir.bootlin.com/linux/v6.18.1/source/drivers/iio/adc/ad9467.c#L916
> 

I agree, not having the scan_mode at all would be more clean.
But adding those different iio_info structs comes across as a bit messy.
Would it make sense to create that iio_info dynamically in the probe and
fill out the callbacks that are supported for the configuration we
encounter? I could try out something like that and see how it would look
like in practice.

Thanks,
Tomas

> Also the channel definition should not have the scan index. But, given that the IIO device
> won't have any buffer I think there's no way to reach ad9467_update_scan_mode() (unless I'm
> missing something).
> 
> Still, while I understand that updating the channels to not include the scan_index is very
> cumbersome, having a new iio_info with no .update_scan_mode() is trivial and make things
> more clear and explicit.
> 
> - Nuno Sá
>