linux-kernel - Re: [PATCH v2 1/8] iio: add read raw service to iio backend framework

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Message-ID: <0a5f82ad9ba032d03b389fce54360a82914c15af.camel@gmail.com>
Date: Wed, 26 Jun 2024 10:50:00 +0200
From: Nuno Sá <noname.nuno@...il.com>
To: Olivier Moysan <olivier.moysan@...s.st.com>,
 fabrice.gasnier@...s.st.com,  Nuno Sa <nuno.sa@...log.com>, Jonathan
 Cameron <jic23@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/8] iio: add read raw service to iio backend
 framework

On Tue, 2024-06-25 at 17:07 +0200, Olivier Moysan wrote:
> Add iio_backend_read_raw() service to support attributes read
> from an IIO backend.
> 
> Signed-off-by: Olivier Moysan <olivier.moysan@...s.st.com>
> Reviewed-by: Nuno Sa <nuno.sa@...log.com>
> ---
>  drivers/iio/industrialio-backend.c | 21 +++++++++++++++++++++
>  include/linux/iio/backend.h        |  6 +++++-
>  2 files changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-
> backend.c
> index 929aff4040ed..0e2653de1956 100644
> --- a/drivers/iio/industrialio-backend.c
> +++ b/drivers/iio/industrialio-backend.c
> @@ -357,6 +357,27 @@ int devm_iio_backend_request_buffer(struct device *dev,
>  }
>  EXPORT_SYMBOL_NS_GPL(devm_iio_backend_request_buffer, IIO_BACKEND);
>  
> +/**
> + * iio_backend_read_raw - Request a channel attribute from the IIO backend.
> + * @back:	Backend device
> + * @chan:	IIO channel reference
> + * @val:	First element of the returned value
> + * @val2:	Second element of the returned value
> + * @mask:	Specify value to retrieve
> + *
> + * This callback replicates the read_raw callback of the IIO framework, and
> is intended to
> + * request miscellaneous channel attributes from the backend device.
> + *
> + * RETURNS:
> + * 0 on success, negative error number on failure.
> + */
> +int iio_backend_read_raw(struct iio_backend *back, struct iio_chan_spec const
> *chan, int *val,
> +			 int *val2, long mask)
> +{
> +	return iio_backend_op_call(back, read_raw, chan, val, val2, mask);
> +}
> +EXPORT_SYMBOL_NS_GPL(iio_backend_read_raw, IIO_BACKEND);

I actually got an idea when looking at this for my existential crisis between
dedicated APIs and a catch all .read_raw() :). What we can do is just provide
the .read_raw() or write_raw() ops to backends (so we minimize the number of
ops) and then we build on top of them for providing more readable (depending on
the case; some cases it does make sense to just call iio_backend_read_raw())
APIs to frontends.

So in your case you could have in backend.h

static inline int iio_backend_read_scale(...)
{
	return iio_backend_read_raw(..., IIO_CHAN_INFO_SCALE);
}

Naturally no need for you to do this right now in your series. Just wanted to
write it down before I go into other stuff and forget about this :)

- Nuno Sá