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

Jonathan Cameron
2026-01-14T12:28:58Z

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");