linux-kernel - Re: [PATCH RFC 3/6] iio: core: Add cleanup.h support for iio_device_claim

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Message-ID: <3b80f8f3-c435-49f8-8c55-42568215bf0b@baylibre.com>
Date: Wed, 3 Dec 2025 15:50:43 -0600
From: David Lechner <dlechner@...libre.com>
To: Kurt Borja <kuurtb@...il.com>,
 Andy Shevchenko <andriy.shevchenko@...el.com>,
 Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Jonathan Cameron <jic23@...nel.org>, Benson Leung <bleung@...omium.org>,
 Antoniu Miclaus <antoniu.miclaus@...log.com>,
 Gwendal Grignou <gwendal@...omium.org>,
 Shrikant Raskar <raskar.shree97@...il.com>,
 Per-Daniel Olsson <perdaniel.olsson@...s.com>
Cc: Nuno Sá <nuno.sa@...log.com>,
 Andy Shevchenko <andy@...nel.org>, Guenter Roeck <groeck@...omium.org>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org, chrome-platform@...ts.linux.dev
Subject: Re: [PATCH RFC 3/6] iio: core: Add cleanup.h support for
 iio_device_claim_*()

On 12/3/25 1:18 PM, Kurt Borja wrote:
> Add guard() and ACQUIRE() support for iio_device_claim_*() lock.
> 
> This involves exporting iio_device_{claim, release}() wrappers to define
> a general GUARD class, and then defining the _direct and _buffer
> conditional ones.

Commit messages should say why we need this.

Also, this seems like two separate things. Adding a new claim/release pair
and adding the conditional guard support to the existing ones. So perhaps
better as two separate patches.

> 
> Suggested-by: Andy Shevchenko <andriy.shevchenko@...el.com>
> Signed-off-by: Kurt Borja <kuurtb@...il.com>
> ---
>  drivers/iio/industrialio-core.c | 12 ++++++++++++
>  include/linux/iio/iio.h         | 20 ++++++++++++++++++++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index adf0142d0300..da090c993fe8 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -2171,6 +2171,18 @@ int __devm_iio_device_register(struct device *dev, struct iio_dev *indio_dev,
>  }
>  EXPORT_SYMBOL_GPL(__devm_iio_device_register);
>  
> +void __iio_device_claim(struct iio_dev *indio_dev)
> +{
> +	mutex_lock(&to_iio_dev_opaque(indio_dev)->mlock);
> +}
> +EXPORT_SYMBOL_GPL(__iio_device_claim);
> +
> +void __iio_device_release(struct iio_dev *indio_dev)
> +{
> +	mutex_unlock(&to_iio_dev_opaque(indio_dev)->mlock);
> +}
> +EXPORT_SYMBOL_GPL(__iio_device_release);
> +
>  /**
>   * __iio_device_claim_direct - Keep device in direct mode
>   * @indio_dev:	the iio_dev associated with the device
> diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
> index 27da9af67c47..472b13ec28d3 100644
> --- a/include/linux/iio/iio.h
> +++ b/include/linux/iio/iio.h
> @@ -10,6 +10,7 @@
>  #include <linux/align.h>
>  #include <linux/device.h>
>  #include <linux/cdev.h>
> +#include <linux/cleanup.h>
>  #include <linux/compiler_types.h>
>  #include <linux/minmax.h>
>  #include <linux/slab.h>
> @@ -661,9 +662,23 @@ void iio_device_unregister(struct iio_dev *indio_dev);
>  int __devm_iio_device_register(struct device *dev, struct iio_dev *indio_dev,
>  			       struct module *this_mod);
>  int iio_push_event(struct iio_dev *indio_dev, u64 ev_code, s64 timestamp);
> +void __iio_device_claim(struct iio_dev *indio_dev);
> +void __iio_device_release(struct iio_dev *indio_dev);
>  bool __iio_device_claim_direct(struct iio_dev *indio_dev);
>  void __iio_device_release_direct(struct iio_dev *indio_dev);
>  
> +static inline void iio_device_claim(struct iio_dev *indio_dev)
> +	__acquires(indio_dev)
> +{
> +	__iio_device_claim(indio_dev);
> +}
> +
> +static inline void iio_device_release(struct iio_dev *indio_dev)
> +	__releases(indio_dev)
> +{
> +	__iio_device_release(indio_dev);
> +}

It was unfortunate that we had to drop "mode" from iio_device_claim_direct_mode()
during the recent API change, but at least it is fairly obvious that "direct"
is a mode. Here, dropping "mode" from the name hurts the understanding. These
could also use some documentation comments to explain what these are for and
when it is appropriate to use them. I had to really dig around the code to
come to the understanding that these mean "don't allow switching modes until
we release the claim".

I would call it something like iio_device_{claim,release}_current_mode().


> +
>  /*
>   * Helper functions that allow claim and release of direct mode
>   * in a fashion that doesn't generate many false positives from sparse.
> @@ -690,6 +705,11 @@ static inline void iio_device_release_direct(struct iio_dev *indio_dev)
>  bool iio_device_claim_buffer(struct iio_dev *indio_dev);
>  void iio_device_release_buffer(struct iio_dev *indio_dev);
>  
> +DEFINE_GUARD(iio_device_claim, struct iio_dev *, iio_device_claim(_T),
> +	     iio_device_release(_T));
> +DEFINE_GUARD_COND(iio_device_claim, _buffer, iio_device_claim_buffer(_T));
> +DEFINE_GUARD_COND(iio_device_claim, _direct, iio_device_claim_direct(_T));
> +
>  extern const struct bus_type iio_bus_type;
>  
>  /**
>