Re: [PATCH v2 3/9] soc: samsung: Add Exynos Adaptive Supply Voltage driver

[Robin Murphy]

On 08/08/2019 13:31, Krzysztof Kozlowski wrote:
> On Thu, 8 Aug 2019 at 14:07, Sylwester Nawrocki <s.nawrocki@xxxxxxxxxxx> wrote:
> > > > +static unsigned int exynos5422_asv_parse_table(struct exynos_asv *asv,
> > > > +                                     unsigned int pkg_id)
> > > > +{
> > > > +       return (pkg_id >> EXYNOS5422_TABLE_OFFSET) & EXYNOS5422_TABLE_MASK;
> > > > +}
> > > > +
> > > > +static bool exynos5422_asv_parse_bin2(struct exynos_asv *asv,
> > > > +                                    unsigned int pkg_id)
> > > > +{
> > > > +       return (pkg_id >> EXYNOS5422_BIN2_OFFSET) & EXYNOS5422_BIN2_MASK;
> > >
> > > return !!() for converting to boolean.
> >
> > I'm not convinced it is needed, the return type of the function is bool
> > and value of the expression will be implicitly converted to that type.
> > Is there any compiler warning related to that?
>
> Yeah, but bool is int so there will be no implicit conversion... I
> guess it is a convention. In theory !! is the proper conversion to
> bool but if bool==int then it's essentially conversion to 1. I am not
> sure what's the benefit, maybe for some wrong code which would do
> comparisons on result like if (exynos5422_asv_parse_bin2() == TRUE)...

Not so - since we use "-std=gnu89", we have C99-like _Bool, which our 
bool is a typedef of. Conversions, either implicit or explicit, are 
well-defined:

"6.3.1.2 Boolean type

When any scalar value is converted to _Bool, the result is 0 if the 
value compares equal
to 0; otherwise, the result is 1."

This is even called out in Documentation/process/coding-style.rst:

"When using bool types the !! construction is not needed, which 
eliminates a class of bugs."

Robin.