Why do we need reset_control_get_optional() ?

[Masahiro Yamada]

Hi Philipp, Arnd.



2016-08-09 1:39 GMT+09:00 Philipp Zabel <p.zabel at pengutronix.de>:
> Am Freitag, den 05.08.2016, 17:50 +0200 schrieb Arnd Bergmann:
>> On Thursday, July 28, 2016 1:00:49 PM CEST Philipp Zabel wrote:
>> > Am Donnerstag, den 28.07.2016, 19:52 +0900 schrieb Masahiro Yamada:
>>
>> > > > In my experimental patch, I make the _optional functions
>> > > > return NULL if no "resets" property is provided but return
>> > > > an error if there are reset lines but the subsystem is
>> > > > disabled, i.e. an optional reset must be used if it's in the
>> > > > DT, but can be ignored otherwise.
>> > >
>> > > I do not like this idea.
>> > >
>> > > reset_control_get() (or variants) should not return NULL, it is ambiguous.
>> > > It should return ERR_PTR(-ENOENT) if no "resets" property.
>> > >
>> > > I only want two types for functions that return a pointer.
>> > >
>> > > [1] return a valid pointer on success, or return NULL on failure
>> > >     (for example, kmalloc())
>> > > [2] return a valid pointer on success, or return error pointer on failure
>> > >    (many of _register() functions)
>> > >
>> > > Mixing [1] and [2] will be a mess.
>>
>> Ah, right. I was thinking only of the case where the reset subsystem
>> is completely disabled here, so returning NULL could be considered
>> a valid return code that can in turn be passed into the other
>> functions.
>>
>> However, I agree that returning NULL as a valid result from
>> ..._get_optional() would be bad style, so let's drop my idea
>> there.
>>
>> > I too would prefer to keep that as-is. The reset_control_get_optional
>> > stub could return -ENOENT if there is no resets device tree property.
>>
>> Now I'm also confused about what we really need
>> reset_control_get_optional() for, and which error codes the callers
>> are supposed to check.
>>
>> This is the matrix I think you mean for _get_optional:
>>
> [...]
>> CONFIG_RESET_CONTROLLER=n, dt entry present: -EOPNOTSUPP
>> CONFIG_RESET_CONTROLLER=n, dt entry missing: -ENOENT
>
> ^^ I didn't consider this distiction.
>
>> Is this what you had in mind? If so, what is the value of the
>> added runtime warning for reset_control_get? Any caller of that
>> function would already check for errors, the only difference
>> I see is that callers of _optional can ignore -ENOENT.
>
> My initial motivation was to make it as hard as possible to misconfigure
> the kernel, which is why I initially didn't want stubs for the
> non-optional variant. Of course that would cause build failures and/or
> reduced compile test coverage, so we added the stubs and the warning to
> make it obvious when a misconfigured kernel is running: on a kernel with
> RESET_CONTROLLER=n drivers that use reset_control_get are expected to
> build, but they are not expected to work. I suppose the same is the case
> for _optional, if the dt entry is present, so maybe we should drop
> reset_control_get_optional and add always a warning in case of
> -EOPNOTSUPP.
> I don't want all drivers to have to differentiate between -EOPNOTSUPP
> and -ENOENT error codes, only current reset_control_get_optional users
> have to do that.


I've posted a patch to drop reset_control_get_optional;
https://patchwork.kernel.org/patch/9284063/

Could you check if it works?

If we go this way, my patch
289363fd99a17d6249ee1373541f1da43cbb22c5
in your reset/next branch is completely useless.

As the commits in the reset-subsystem do not appear
even in linux-next until they are pulled into the ASOC tree,
how about dropping 289363fd and turning around?


-- 
Best Regards
Masahiro Yamada