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

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Date:   Tue, 20 Jun 2023 17:47:34 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Lucas De Marchi <lucas.demarchi@...el.com>,
        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 Thu, 15 Jun 2023, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> On Fri, May 12, 2023 at 02:45:19PM +0300, Jani Nikula wrote:
>> On Fri, 12 May 2023, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
>> > On Fri, May 12, 2023 at 02:25:18PM +0300, Jani Nikula wrote:
>> >> 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.
>> >
>> > When needed GENMASK_ULL() can be used (with respective castings perhaps)
>> > and BIT_ULL(), no?
>> 
>> How does that help with making them the same 32-bit size on both 32 and
>> 64 bit builds?
>
> 	u32 x = GENMASK();
> 	u64 y = GENMASK_ULL();
>
> No? Then use in your code either x or y. Note that I assume that the parameters
> to GENMASK*() are built-time constants. Is it the case for you?

What's wrong with wanting to define macros with specific size, depending
on e.g. hardware registers instead of build size?

What would you use for printk format if you wanted to to print
GENMASK()?


BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center