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

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Date:   Thu, 15 Jun 2023 18:58:33 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     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>,
        Jani Nikula <jani.nikula@...ux.intel.com>
Subject: Re: [PATCH 2/3] linux/bits.h: Add fixed-width GENMASK and BIT macros

On Fri, May 12, 2023 at 09:29:23AM -0700, Lucas De Marchi wrote:
> On Fri, May 12, 2023 at 02:14:19PM +0300, Andy Shevchenko 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?
> 
> to create the masks/values for device registers that are
> of a certain width, preventing mistakes like:
> 
> 	#define REG1		0x10
> 	#define REG1_ENABLE	BIT(17)
> 	#define REG1_FOO	GENMASK(16, 15);
> 
> 	register_write(REG1_ENABLE, REG1);
> 
> 
> ... if REG1 is a 16bit register for example. There were mistakes in the
> past in the i915 source leading to the creation of the REG_* variants on
> top of normal GENMASK/BIT (see last patch and commit 09b434d4f6d2
> ("drm/i915: introduce REG_BIT() and REG_GENMASK() to define register
> contents")

Doesn't it look like something for bitfield.h candidate?
If your definition doesn't fit the given mask, bail out.

-- 
With Best Regards,
Andy Shevchenko