linux-kernel - Re: [PATCH RFC 5/6] iio: health: max30102: Use cleanup.h for IIO locks

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Message-Id: <DEPLIJFBZQ36.20XX5DCMCJVB3@gmail.com>
Date: Thu, 04 Dec 2025 12:07:43 -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 RFC 5/6] iio: health: max30102: Use cleanup.h for IIO
 locks

On Wed Dec 3, 2025 at 4:52 PM -05, David Lechner wrote:
> On 12/3/25 1:18 PM, Kurt Borja wrote:
>> Simplify and drop "hacky" busy-waiting code in max30102_read_raw() by
>> using scoped_guard().
>> 
>> Signed-off-by: Kurt Borja <kuurtb@...il.com>
>> ---
>>  drivers/iio/health/max30102.c | 24 +++++++-----------------
>>  1 file changed, 7 insertions(+), 17 deletions(-)
>> 
>> diff --git a/drivers/iio/health/max30102.c b/drivers/iio/health/max30102.c
>> index 678720102f2b..c642842cb5fb 100644
>> --- a/drivers/iio/health/max30102.c
>> +++ b/drivers/iio/health/max30102.c
>> @@ -24,6 +24,7 @@
>>  #include <linux/iio/iio.h>
>>  #include <linux/iio/buffer.h>
>>  #include <linux/iio/kfifo_buf.h>
>> +#include <linux/cleanup.h>
>>  
>>  #define MAX30102_DRV_NAME	"max30102"
>>  #define MAX30102_PART_NUMBER	0x15
>> @@ -468,6 +469,7 @@ static int max30102_read_raw(struct iio_dev *indio_dev,
>>  {
>>  	struct max30102_data *data = iio_priv(indio_dev);
>>  	int ret = -EINVAL;
>> +	bool direct_en;
>>  
>>  	switch (mask) {
>>  	case IIO_CHAN_INFO_RAW:
>> @@ -475,25 +477,13 @@ static int max30102_read_raw(struct iio_dev *indio_dev,
>>  		 * Temperature reading can only be acquired when not in
>>  		 * shutdown; leave shutdown briefly when buffer not running
>>  		 */
>> -any_mode_retry:
>> -		if (!iio_device_claim_buffer(indio_dev)) {
>> -			/*
>> -			 * This one is a *bit* hacky. If we cannot claim buffer
>> -			 * mode, then try direct mode so that we make sure
>> -			 * things cannot concurrently change. And we just keep
>> -			 * trying until we get one of the modes...
>> -			 */
>> -			if (!iio_device_claim_direct(indio_dev))
>> -				goto any_mode_retry;
>> +		scoped_guard(iio_device_claim, indio_dev) {
>
> scoped_guard() is sketchy in switch statements because there is
> a hidden for loop. If someone came along later and put a break;
> inside of the scope, it would break out of the hidden for loop
> rather than the apparent switch case!
>
> Besides that, it adds extra indent that we could avoid.
>
>> +			direct_en = !iio_buffer_enabled(indio_dev);
>>  
>> -			ret = max30102_get_temp(data, val, true);
>> -			iio_device_release_direct(indio_dev);
>> -		} else {
>> -			ret = max30102_get_temp(data, val, false);
>> -			iio_device_release_buffer(indio_dev);
>> +			ret = max30102_get_temp(data, val, direct_en);
>> +			if (ret)
>> +				return ret;
>>  		}
>> -		if (ret)
>> -			return ret;
>>  
>>  		ret = IIO_VAL_INT;
>>  		break;
>> 
>
> I would write the whole function like this:
>
> static int max30102_read_raw(struct iio_dev *indio_dev,
> 			     struct iio_chan_spec const *chan,
> 			     int *val, int *val2, long mask)
> {
> 	struct max30102_data *data = iio_priv(indio_dev);
> 	int ret;
>
> 	switch (mask) {
> 	case IIO_CHAN_INFO_RAW: {
> 		/*
> 		 * Temperature reading can only be acquired when not in
> 		 * shutdown; leave shutdown briefly when buffer not running
> 		 */
> 		guard(iio_device_claim)(indio_dev);

AFAIK you can't guard() inside switch-case blocks. I don't know the
exact reason, but it has to be scoped_guard().

> 		ret = max30102_get_temp(data, val, !iio_buffer_enabled(indio_dev));
> 		if (ret)
> 			return ret;
>
> 		return IIO_VAL_INT;
> 	}
> 	case IIO_CHAN_INFO_SCALE:
> 		*val = 1000;  /* 62.5 */
> 		*val2 = 16;
> 		return IIO_VAL_FRACTIONAL;
> 	default:
> 		return -EINVAL;
> 	}
> }
>
> Could also simplify things further by moving the call to iio_buffer_enabled()
> into max30102_get_temp().

I'll do it like this if this survives v2.


-- 
 ~ Kurt