linux-kernel - Re: [PATCH] reset: Make optional functions really optional.

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Date:   Fri, 23 Dec 2016 16:53:51 +0000
From:   Ramiro Oliveira <Ramiro.Oliveira@...opsys.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Philipp Zabel <p.zabel@...gutronix.de>
CC:     Ramiro Oliveira <Ramiro.Oliveira@...opsys.com>,
        <linux-kernel@...r.kernel.org>, <CARLOS.PALMINHA@...opsys.com>
Subject: Re: [PATCH] reset: Make optional functions really optional.

Hi Laurent and Philipp

On 12/23/2016 4:41 PM, Laurent Pinchart wrote:
> Hi Philipp,
> 
> On Friday 23 Dec 2016 13:08:54 Philipp Zabel wrote:
>> Am Freitag, den 23.12.2016, 13:23 +0200 schrieb Laurent Pinchart:
>>> On Friday 23 Dec 2016 11:58:57 Philipp Zabel wrote:
>>>> Am Donnerstag, den 15.12.2016, 18:05 +0000 schrieb Ramiro Oliveira:
>>>>> Up until now optional functions in the reset API were similar to the
>>>>> non optional.
>>>>>
>>>>> This patch corrects that, while maintaining compatibility with
>>>>> existing drivers.
>>>>>
>>>>> As suggested here: https://urldefense.proofpoint.com/v2/url?u=https-3A__lkml.org_lkml_2016_12_14_502&d=DgICAg&c=DPL6_X_6JkXFx7AXWqB0tg&r=BHEb-RADEOm-lgrwdN4zqtr2BWZMjeocyTkjphE6PrA&m=8s4unvlk7rXGYKdQcMBxpYLmdnROh5aQ_iHU03InFoM&s=oNBgTOo47LBs0JvtJ5Qd_6uVqrcMkWAq1PmNN4qt16g&e= 
>>>>>
>>>>> Signed-off-by: Ramiro Oliveira <Ramiro.Oliveira@...opsys.com>
>>>>> ---
>>>>>
>>>>>  drivers/reset/core.c  | 21 +++++++++++++++++++--
>>>>>  include/linux/reset.h | 46 ++++++++++++++++++++++++++++++++++++++----
>>>>>  2 files changed, 61 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/reset/core.c b/drivers/reset/core.c
>>>>> index 395dc9c..6150e7c 100644
>>>>> --- a/drivers/reset/core.c
>>>>> +++ b/drivers/reset/core.c
>>>>> @@ -135,9 +135,14 @@
>>>>> EXPORT_SYMBOL_GPL(devm_reset_controller_register);
>>>>>   * @rstc: reset controller
>>>>>   *
>>>>>   * Calling this on a shared reset controller is an error.
>>>>> + *
>>>>> + * If it's an optional reset it will return 0.
>>>>
>>>> I'd prefer this to explicitly mention that rstc==NULL means this is an
>>>> optional reset:
>>>>
>>>> "If rstc is NULL it is an optional reset and the function will just
>>>> return 0."
>>>
>>> Maybe we should document in a single place that NULL is a valid value for
>>> a reset_control pointer and will result in the API behaving as a no-op ?
>>> If you want to duplicate the information I'd still prefer talking about
>>> no-op than about "just returning 0".
>>
>> Does "no-op" implicate the return value 0? Maybe there is a better way
>> to express "no action, returns 0".
> 
> The important point in my opinion is that a NULL argument will result in the 
> function performing no operation and indicating success exactly like a call 
> with a non-NULL pointer would. The proposed text makes it sound like a 0 
> return value is specific to the NULL argument case. This is a detail though.
> 

"If rstc is NULL it is an optional reset and the function will just return 0
like any other successful call."

Do you guys think the above message is more explicit?

>> Currently there is no central place for this information, and as long as
>> the text not much longer than a reference to the central location would
>> be, I'm fine with duplication.
>>
>>>>>   */
>>>>>  int reset_control_reset(struct reset_control *rstc)
>>>>>  {
>>>>> +	if (!rstc)
>>>>> +		return 0;
>>>>> +
>>>>>  	if (WARN_ON(rstc->shared))
>>>>>  		return -EINVAL;
>