On 04/09/2024 20:21, Dmitry Torokhov wrote:
> Hi Javier,
>
> On Wed, Sep 04, 2024 at 03:53:40PM +0200, Javier Carrasco wrote:
>> On 04/09/2024 06:47, Dmitry Torokhov wrote:
>>> Using guard notation makes the code more compact and error handling
>>> more robust by ensuring that mutexes are released in all code paths
>>> when control leaves critical section.
>>>
>>> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
>>> ---
>>> drivers/input/misc/iqs269a.c | 46 +++++++++++++-----------------------
>>> 1 file changed, 16 insertions(+), 30 deletions(-)
>>>
>>> diff --git a/drivers/input/misc/iqs269a.c b/drivers/input/misc/iqs269a.c
>>> index 843f8a3f3410..c34d847fa4af 100644
>>> --- a/drivers/input/misc/iqs269a.c
>>> +++ b/drivers/input/misc/iqs269a.c
>>
>> ...
>>
>>> @@ -453,9 +449,9 @@ static int iqs269_ati_base_get(struct iqs269_private *iqs269,
>>> if (ch_num >= IQS269_NUM_CH)
>>> return -EINVAL;
>>>
>>> - mutex_lock(&iqs269->lock);
>>> + guard(mutex)(&iqs269->lock);
>>> +
>>> engine_b = be16_to_cpu(ch_reg[ch_num].engine_b);
>>
>> maybe scoped_guard() to keep the scope of the mutex as it used to be?
>
> Thank you for looking over patches.
>
> It is just a few computations extra, so I decided not to use
> scoped_guard(). Note that original code was forced to release mutex
> early to avoid having to unlock it in all switch branches.
>
>>
>>> - mutex_unlock(&iqs269->lock);
>>>
>>> switch (engine_b & IQS269_CHx_ENG_B_ATI_BASE_MASK) {
>>> case IQS269_CHx_ENG_B_ATI_BASE_75:
>>> @@ -491,7 +487,7 @@ static int iqs269_ati_target_set(struct iqs269_private *iqs269,
>>> if (target > IQS269_CHx_ENG_B_ATI_TARGET_MAX)
>>> return -EINVAL;
>>>
>>> - mutex_lock(&iqs269->lock);
>>> + guard(mutex)(&iqs269->lock);
>>>
>>> engine_b = be16_to_cpu(ch_reg[ch_num].engine_b);
>>>
>>> @@ -501,8 +497,6 @@ static int iqs269_ati_target_set(struct iqs269_private *iqs269,
>>> ch_reg[ch_num].engine_b = cpu_to_be16(engine_b);
>>> iqs269->ati_current = false;
>>>
>>> - mutex_unlock(&iqs269->lock);
>>> -
>>> return 0;
>>> }
>>>
>>> @@ -515,10 +509,9 @@ static int iqs269_ati_target_get(struct iqs269_private *iqs269,
>>> if (ch_num >= IQS269_NUM_CH)
>>> return -EINVAL;
>>>
>>> - mutex_lock(&iqs269->lock);
>>> - engine_b = be16_to_cpu(ch_reg[ch_num].engine_b);
>>> - mutex_unlock(&iqs269->lock);
>>> + guard(mutex)(&iqs269->lock);
>>
>> same here?
>>
>>>
>>> + engine_b = be16_to_cpu(ch_reg[ch_num].engine_b);
>>> *target = (engine_b & IQS269_CHx_ENG_B_ATI_TARGET_MASK) * 32;
>
> Same here, calculating the line above will take no time at all...
>
> Thanks.
>
As you pointed out, in reality the extra locked instructions will not
make any difference. But as the conversion added instructions to be
locked by the mutex without mentioning it, I thought it should be either
left as it used to be with scoped_guard(), or explicitly mentioned in
the description.
No strong feelings against it, but out of curiosity, why would you
rather use guard()? I think scoped_guard() is a better way to
self-document what has to be accessed via mutex, and what not.
Best regards,
Javier Carrasco
