linux-kernel - Re: [PATCH v3 4/7] iio: core: Add cleanup.h support for iio_device_claim

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Message-Id: <DFRTH0GI1UPO.12NSSABBNSRST@gmail.com>
Date: Sun, 18 Jan 2026 10:23:10 -0500
From: "Kurt Borja" <kuurtb@...il.com>
To: "David Lechner" <dlechner@...libre.com>, "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 v3 4/7] iio: core: Add cleanup.h support for
 iio_device_claim_*()

On Fri Jan 16, 2026 at 5:03 PM -05, David Lechner wrote:
> On 1/6/26 2:06 AM, Kurt Borja wrote:
>> Add guard classes for iio_device_claim_*() conditional locks. This will
>> aid drivers write safer and cleaner code when dealing with some common
>> patterns.
>> 
>> These classes are not meant to be used directly by drivers (hence the
>> __priv__ prefix). Instead, documented wrapper macros are provided to
>> enforce the use of ACQUIRE() or guard() semantics and avoid the
>> problematic scoped guard.
>> 
>> Suggested-by: Andy Shevchenko <andriy.shevchenko@...el.com>
>> Signed-off-by: Kurt Borja <kuurtb@...il.com>
>> ---
>>  include/linux/iio/iio.h | 71 +++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 71 insertions(+)
>> 
>> diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
>> index d8af0456f966..c795f731f2d8 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>
>> @@ -740,6 +741,76 @@ static inline bool iio_device_try_claim_buffer_mode(struct iio_dev *indio_dev)
>>   */
>>  #define iio_device_release_buffer_mode(indio_dev) __iio_dev_mode_unlock(indio_dev)
>>  
>> +/*
>> + * These classes are not meant to be used directly by drivers (hence the
>> + * __priv__ prefix). Instead, documented wrapper macros are provided bellow to
>> + * enforce the use of ACQUIRE() or guard() semantics and avoid the problematic
>> + * scoped guard variants.
>> + */
>> +DEFINE_GUARD(__priv__iio_dev_mode_lock, struct iio_dev *,
>> +	     __iio_dev_mode_lock(_T), __iio_dev_mode_unlock(_T));
>> +DEFINE_GUARD_COND(__priv__iio_dev_mode_lock, _try_direct,
>> +		  iio_device_claim_direct(_T));
>> +
>> +/**
>> + * IIO_DEV_ACQUIRE_DIRECT_MODE(_dev, _var) - Tries to acquire the direct mode
>> + *                                           lock with automatic release
>
> I don't think it is usual to put the function parameters in the
> doc comment like this. They don't match the actual names anyway.

Hi David,

This format of kernel-doc applies to function-like macros too [1]. I'll
match the name of the variables though.

>
>> + * @dev: IIO device instance
>> + * @claim: Variable identifier to store acquire result
>> + *
>> + * Tries to acquire the direct mode lock with cleanup ACQUIRE() semantics and
>> + * automatically releases it at the end of the scope. It most be always paired
>> + * with IIO_DEV_ACQUIRE_ERR(), for example::
>> + *
>> + *	IIO_DEV_ACQUIRE_DIRECT_MODE(indio_dev, claim);
>> + *	if (IIO_DEV_ACQUIRE_FAILED(&claim))
>> + *		return -EBUSY;
>> + *
>> + * ...or a more common scenario (notice scope the braces)::
>> + *
>> + *	switch() {
>> + *	case IIO_CHAN_INFO_RAW: {
>> + *		IIO_DEV_ACQUIRE_DIRECT_MODE(indio_dev, claim);
>> + *		if (IIO_DEV_ACQUIRE_FAILED(&claim))
>> + *			return -EBUSY;
>> + *
>> + *		...
>> + *	}
>> + *	case IIO_CHAN_INFO_SCALE:
>> + *		...
>> + *	...
>> + *	}
>> + *
>> + * Context: Can sleep
>> + */
>> +#define IIO_DEV_ACQUIRE_DIRECT_MODE(dev, claim) \
>> +	ACQUIRE(__priv__iio_dev_mode_lock_try_direct, claim)(dev)
>> +
>> +/**
>> + * IIO_DEV_ACQUIRE_FAILED() - ACQUIRE_ERR() wrapper
>> + * @claim_ptr: Pointer to the claim variable passed to IIO_DEV_ACQUIRE_*_MODE()
>> + *
>> + * Return: true if acquired the mode failed, otherwise false.
>> + */
>> +#define IIO_DEV_ACQUIRE_FAILED(claim_ptr) \
>> +	ACQUIRE_ERR(__priv__iio_dev_mode_lock_try_direct, claim_ptr)
>> +
>
> If we always have to add the & at the call site, could we just
> put that in the macro instead? Then the parameter would just be
> claim instead of claim_ptr.

I'll add this in the next revision.

[1] https://docs.kernel.org/doc-guide/kernel-doc.html#function-documentation

-- 
Thanks,
 ~ Kurt