linux-kernel - Re: [PATCH v3 1/3] bits: introduce fixed-type genmasks

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Message-ID: <ZeBhVb__VNQCgTQk@smile.fi.intel.com>
Date: Thu, 29 Feb 2024 12:49:57 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Lucas De Marchi <lucas.demarchi@...el.com>
Cc: Yury Norov <yury.norov@...il.com>,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	intel-xe@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
	Jani Nikula <jani.nikula@...el.com>
Subject: Re: [PATCH v3 1/3] bits: introduce fixed-type genmasks

On Wed, Feb 28, 2024 at 05:39:21PM -0600, Lucas De Marchi wrote:
> On Thu, Feb 22, 2024 at 06:49:59AM -0800, Yury Norov wrote:
> > On Wed, Feb 21, 2024 at 03:59:06PM -0600, Lucas De Marchi wrote:
> > > On Wed, Feb 21, 2024 at 11:04:22PM +0200, Andy Shevchenko wrote:
> > > > On Wed, Feb 21, 2024 at 10:30:02PM +0200, Dmitry Baryshkov wrote:
> > > > > On Thu, 8 Feb 2024 at 09:45, Lucas De Marchi <lucas.demarchi@...el.com> wrote:

..

> I build-tested this in x86-64, x86-32 and arm64. I didn't like much the
> need to fork the __GENMASK() implementation on the 2 sides of the ifdef
> since I think the GENMASK_INPUT_CHECK() should be the one covering the
> input checks. However to make it common we'd need to solve 2 problems:
> the casts and the sizeof. The sizeof can be passed as arg to
> __GENMASK(), however the casts I think would need a __CAST_U8(x)
> or the like and sprinkle it everywhere, which would hurt readability.
> Not pretty. Or go back to the original submission and make it less
> horrible :-/

I'm wondering if we can use _Generic() approach here.

..

> > #define GENMASK_INPUT_CHECK(h, l) 0
> > +#define __GENMASK(t, h, l) \
> > +	((~0 - (1 << (l)) + 1) & (~0 >> (BITS_PER_LONG - 1 - (h))))
> 
> humn... this builds, but does it work if GENMASK_ULL() is used in
> assembly? That BITS_PER_LONG does not match the type width.

UL()/ULL() macros are not just for fun.

-- 
With Best Regards,
Andy Shevchenko