Re: [PATCH v3 2/4] iio: industrialio-backend: support backend capabilities

[Jonathan Cameron <jonathan.cameron@huawei.com>]

On Wed, 14 Jan 2026 10:45:51 +0000
Tomas Melin <tomas.melin@vaisala.com> wrote:

> Not all backends support the full set of capabilities provided by the
> industrialio-backend framework. Capability bits can be used in frontends
> and backends for checking for a certain feature set, or if using
> related functions can be expected to fail.
> 
> Capability bits should be set by a compatible backend and provided when
> registering the backend.
> 
> Signed-off-by: Tomas Melin <tomas.melin@vaisala.com>
Hi Tomas,

One thing inline.

Thanks

Jonathan


> ---
>  drivers/iio/industrialio-backend.c | 17 +++++++++++++++++
>  include/linux/iio/backend.h        | 17 +++++++++++++++++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
> index 447b694d6d5f72dc6f018b1697fdb88e555bd61e..0a98fdd5df9db6cc233af819ac5243ba8cd5266f 100644
> --- a/drivers/iio/industrialio-backend.c
> +++ b/drivers/iio/industrialio-backend.c
> @@ -56,6 +56,7 @@ struct iio_backend {
>  	void *priv;
>  	const char *name;
>  	unsigned int cached_reg_addr;
> +	u32 caps;
>  	/*
>  	 * This index is relative to the frontend. Meaning that for
>  	 * frontends with multiple backends, this will be the index of this
> @@ -774,6 +775,21 @@ int iio_backend_extend_chan_spec(struct iio_backend *back,
>  }
>  EXPORT_SYMBOL_NS_GPL(iio_backend_extend_chan_spec, "IIO_BACKEND");
>  
> +/**
> + * iio_backend_has_caps - Check if backend has specific capabilities
> + * @back: Backend device
> + * @caps: Capabilities to check
> + *
> + * RETURNS:
> + * Non-zero value if backend has all the requested capabilities,

It doesn't...   back->caps = 0x1, caps = 0x3 returns 0x1 which
is non-zero.   I'd do
return (back->caps & caps) == caps;

Though that also rather strongly indicates this would be better returning
a bool.


> + * 0 otherwise.
> + */
> +int iio_backend_has_caps(struct iio_backend *back, u32 caps)
> +{
> +	return back->caps & caps;
> +}
> +EXPORT_SYMBOL_NS_GPL(iio_backend_has_caps, "IIO_BACKEND");