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From:   Jani Nikula <jani.nikula@linux.intel.com>
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Lucas De Marchi <lucas.demarchi@intel.com>
Cc:     intel-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org,
        dri-devel@lists.freedesktop.org,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org,
        Masahiro Yamada <masahiroy@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Christian =?utf-8?Q?K=C3=B6nig?= <christian.koenig@amd.com>
Subject: Re: [PATCH 2/3] linux/bits.h: Add fixed-width GENMASK and BIT macros
In-Reply-To: <ZF4fi5B7PPlgZBOI@smile.fi.intel.com>
Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo
References: <20230509051403.2748545-1-lucas.demarchi@intel.com>
 <20230509051403.2748545-3-lucas.demarchi@intel.com>
 <ZF4fi5B7PPlgZBOI@smile.fi.intel.com>
Date:   Fri, 12 May 2023 14:25:18 +0300
Message-ID: <87pm75kd0h.fsf@intel.com>
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On Fri, 12 May 2023, Andy Shevchenko <andriy.shevchenko@linux.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