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 17:55:19 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Jani Nikula <jani.nikula@...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 Tue, Jun 20, 2023 at 05:47:34PM +0300, Jani Nikula wrote:
> 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?

Nothing, but I think the problem is smaller than it's presented.
And there are already header for bitfields with a lot of helpers
for (similar) cases if not yours.

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

%lu, no?

-- 
With Best Regards,
Andy Shevchenko