linux-kernel - Re: [PATCH 00/14] drm/tidss: dispc: Convert to FIELD

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Message-ID: <20250731-observant-fervent-heron-dbe833@houat>
Date: Thu, 31 Jul 2025 16:05:07 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Louis Chauvet <louis.chauvet@...tlin.com>
Cc: Jyri Sarha <jyri.sarha@....fi>, 
	Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/14] drm/tidss: dispc: Convert to FIELD_* API

On Thu, Jul 31, 2025 at 03:49:12PM +0200, Louis Chauvet wrote:
> 
> 
> Le 31/07/2025 à 15:26, Maxime Ripard a écrit :
> > Hi Louis,
> > 
> > On Thu, Jul 31, 2025 at 03:04:49PM +0200, Louis Chauvet wrote:
> > > Le 30/07/2025 à 10:57, Maxime Ripard a écrit :
> > > > Hi,
> > > > 
> > > > The tidss driver rolls its own API equivalent to the FIELD_* API already
> > > > provided the kernel.
> > > > 
> > > > Since it's an ad-hoc implementation, it also is less convenient and
> > > > doesn't provide some useful features like being able to share the field
> > > > definitions that will come handy in the future.
> > > > 
> > > > Thus, this series converts the driver to that API and drops its own
> > > > version.
> > > 
> > > I just saw your series after sending mine [2]. I checked, there is only one
> > > minor conflict that can be easly fixed.
> > > 
> > > But when applied on drm-misc/drm-misc-next, your series raises:
> > > 
> > > In file included from <command-line>:
> > > drivers/gpu/drm/tidss/tidss_dispc.c: In function 'FLD_MOD':
> > > ././include/linux/compiler_types.h:568:45: error: call to
> > > '__compiletime_assert_589' declared with attribute error: FIELD_PREP: mask
> > > is not constant
> > >    568 |         _compiletime_assert(condition, msg, __compiletime_assert_,
> > > __COUNTER__)
> > >        |                                             ^
> > > ././include/linux/compiler_types.h:549:25: note: in definition of macro
> > > '__compiletime_assert'
> > >    549 |                         prefix ## suffix();         \
> > >        |                         ^~~~~~
> > > ././include/linux/compiler_types.h:568:9: note: in expansion of macro
> > > '_compiletime_assert'
> > >    568 |         _compiletime_assert(condition, msg, __compiletime_assert_,
> > > __COUNTER__)
> > >        |         ^~~~~~~~~~~~~~~~~~~
> > > ./include/linux/build_bug.h:39:37: note: in expansion of macro
> > > 'compiletime_assert'
> > >     39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
> > >        |                                     ^~~~~~~~~~~~~~~~~~
> > > ./include/linux/bitfield.h:65:17: note: in expansion of macro
> > > 'BUILD_BUG_ON_MSG'
> > >     65 |                 BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask),
> > > \
> > >        |                 ^~~~~~~~~~~~~~~~
> > > ./include/linux/bitfield.h:115:17: note: in expansion of macro
> > > '__BF_FIELD_CHECK'
> > >    115 |                 __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: ");
> > > \
> > >        |                 ^~~~~~~~~~~~~~~~
> > > drivers/gpu/drm/tidss/tidss_dispc.c:599:33: note: in expansion of macro
> > > 'FIELD_PREP'
> > >    599 |         return (orig & ~mask) | FIELD_PREP(mask, val);
> > >        |                                 ^~~~~~~~~~
> > > 
> > > 
> > > This seems to be a limitation of FIELD_PREP [1].
> > > I think the only way to avoid this issue is to use macros and not functions.
> > > 
> > > [1]:https://elixir.bootlin.com/linux/v6.16/source/include/linux/bitfield.h#L65-L66
> > > [2]:https://lore.kernel.org/all/20250730-fix-edge-handling-v1-0-1bdfb3fe7922@bootlin.com/
> > 
> > Weird, it compiles without warning for me here. Which compiler do you use?
> 
> 
> I use this one:
> 
> aarch64-linux-gnu-gcc (GCC) 14.2.1 20240912 (Red Hat Cross 14.2.1-2)
> Copyright (C) 2024 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.  There is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

I was testing with clang, but I can indeed see it with gcc. I'll fix it. Thanks!

Maxime

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