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Subject: Re: [PATCH v2 3/9] soc: samsung: Add Exynos Adaptive Supply Voltage
 driver
To:     Krzysztof Kozlowski <krzk@kernel.org>,
        Sylwester Nawrocki <s.nawrocki@samsung.com>
Cc:     devicetree@vger.kernel.org,
        "linux-samsung-soc@vger.kernel.org" 
        <linux-samsung-soc@vger.kernel.org>, linux-pm@vger.kernel.org,
        pankaj.dubey@samsung.com,
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        <b.zolnierkie@samsung.com>,
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        robh+dt@kernel.org, kgene@kernel.org, vireshk@kernel.org,
        linux-arm-kernel@lists.infradead.org,
        Marek Szyprowski <m.szyprowski@samsung.com>
References: <CGME20190718143130eucas1p26f2058f47eb2f4020e1ddbf1619d1ac8@eucas1p2.samsung.com>
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From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <669c6b25-eb7e-ed3a-72a2-ee155a568363@arm.com>
Date:   Thu, 8 Aug 2019 13:48:24 +0100
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On 08/08/2019 13:31, Krzysztof Kozlowski wrote:
> On Thu, 8 Aug 2019 at 14:07, Sylwester Nawrocki <s.nawrocki@samsung.com> 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.