linux-kernel - Re: [PATCH 2/3] linux/bits.h: Add fixed-width GENMASK and BIT macros

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Date:   Fri, 12 May 2023 14:25:18 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Lucas De Marchi <lucas.demarchi@...el.com>
Cc:     intel-gfx@...ts.freedesktop.org, intel-xe@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH 2/3] linux/bits.h: Add fixed-width GENMASK and BIT macros

On Fri, 12 May 2023, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> On Mon, May 08, 2023 at 10:14:02PM -0700, Lucas De Marchi wrote:
>> Add GENMASK_U32(), GENMASK_U16() and GENMASK_U8()  macros to create
>> masks for fixed-width types and also the corresponding BIT_U32(),
>> BIT_U16() and BIT_U8().
>
> Why?

The main reason is that GENMASK() and BIT() size varies for 32/64 bit
builds.


BR,
Jani.

>
>> All of those depend on a new "U" suffix added to the integer constant.
>> Due to naming clashes it's better to call the macro U32. Since C doesn't
>> have a proper suffix for short and char types, the U16 and U18 variants
>> just use U32 with one additional check in the BIT_* macros to make
>> sure the compiler gives an error when the those types overflow.
>> The BIT_U16() and BIT_U8() need the help of GENMASK_INPUT_CHECK(),
>> as otherwise they would allow an invalid bit to be passed. Hence
>> implement them in include/linux/bits.h rather than together with
>> the other BIT* variants.
>
> So, we have _Generic() in case you still wish to implement this.

-- 
Jani Nikula, Intel Open Source Graphics Center