Re: [PATCH 5/8] iio: accel: kx022a: Switch to sparse friendly iio_device_claim/release_direct()

[Matti Vaittinen <mazziesaccount@gmail.com>]

On 18/02/2025 17:42, David Lechner wrote:
> On 2/18/25 1:39 AM, Matti Vaittinen wrote:
>> On 17/02/2025 16:01, Jonathan Cameron wrote:
>>> From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>>>
>>> These new functions allow sparse to find failures to release
>>> direct mode reducing chances of bugs over the claim_direct_mode()
>>> functions that are deprecated.
>>>
>>> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>>> Cc: Matti Vaittinen <mazziesaccount@gmail.com>
>>> ---
>>>    drivers/iio/accel/kionix-kx022a.c | 14 ++++++--------
>>>    1 file changed, 6 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/drivers/iio/accel/kionix-kx022a.c b/drivers/iio/accel/kionix-kx022a.c
>>> index 727e007c5fc1..07dcf5f0599f 100644
>>> --- a/drivers/iio/accel/kionix-kx022a.c
>>> +++ b/drivers/iio/accel/kionix-kx022a.c
>>> @@ -577,13 +577,12 @@ static int kx022a_write_raw(struct iio_dev *idev,
>>>         * issues if users trust the watermark to be reached within known
>>>         * time-limit).
>>>         */
>>> -    ret = iio_device_claim_direct_mode(idev);
>>> -    if (ret)
>>> -        return ret;
>>> +    if (!iio_device_claim_direct(idev))
>>> +        return -EBUSY;
>>
>> Not really in the scope of this review - but in my opinion the logic of this check is terribly counter intuitive. I mean,
>>
>>> +    if (iio_device_claim_direct(idev))
>>> +        return -EBUSY;
> 
> I'm curious how you read this then. I read this as:
> 
> "If claiming direct mode succeeded, then return an error!"

I am used to seeing a pattern where function returning zero indicates a 
success. I have no statistics but I believe this is true for a vast 
majority of functions in the kernel. I believe this was the case with 
the old 'iio_device_claim_direct_mode(idev)' too.

I am not saying this is 'absolutely' bad. I can only tell that _I_ 
really had to go and look up the implementation of the 
iio_device_claim_direct() in order to review this change to ensure the 
return value check was not inverted.

Yours,
	-- Matti