linux-kernel - Re: include/linux/compiler_types.h:597:38: error: call to '__compiletime_assert_495' declared with attribute error: FIELD

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Message-ID: <c2f6eb5f-0eb6-47c4-9627-d2a5dfd6abd4@mailbox.org>
Date: Fri, 23 Jan 2026 11:15:35 +0100
From: Marek Vasut <marek.vasut@...lbox.org>
To: kernel test robot <lkp@...el.com>,
 Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
 Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>
Cc: oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Subject: Re: include/linux/compiler_types.h:597:38: error: call to
 '__compiletime_assert_495' declared with attribute error: FIELD_PREP: value
 too large for the field

On 1/23/26 1:58 AM, kernel test robot wrote:
> Hi Marek,
> 
> FYI, the error/warning still remains.
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   a66191c590b3b58eaff05d2277971f854772bd5b
> commit: 4f716a1db661cfb31502a0a6d7e62c06daf2e603 drm/rcar-du: dsi: Convert register bitfields to GENMASK() macro
> date:   3 months ago
> config: arc-randconfig-r053-20260123 (https://download.01.org/0day-ci/archive/20260123/202601230809.FBjF6OrH-lkp@intel.com/config)
> compiler: arc-linux-gcc (GCC) 8.5.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260123/202601230809.FBjF6OrH-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202601230809.FBjF6OrH-lkp@intel.com/
> 
> All errors (new ones prefixed by >>):
> 
>     In file included from <command-line>:
>     drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c: In function 'rcar_mipi_dsi_startup.isra.6':
>>> include/linux/compiler_types.h:597:38: error: call to '__compiletime_assert_495' declared with attribute error: FIELD_PREP: value too large for the field
>       _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>                                           ^
>     include/linux/compiler_types.h:578:4: note: in definition of macro '__compiletime_assert'
>         prefix ## suffix();    \
>         ^~~~~~
>     include/linux/compiler_types.h:597:2: note: in expansion of macro '_compiletime_assert'
>       _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>       ^~~~~~~~~~~~~~~~~~~
>     include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
>      #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>                                          ^~~~~~~~~~~~~~~~~~
>     include/linux/bitfield.h:68:3: note: in expansion of macro 'BUILD_BUG_ON_MSG'
>        BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ?  \
>        ^~~~~~~~~~~~~~~~
>     include/linux/bitfield.h:115:3: note: in expansion of macro '__BF_FIELD_CHECK'
>        __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: "); \
>        ^~~~~~~~~~~~~~~~
>     drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi_regs.h:259:29: note: in expansion of macro 'FIELD_PREP'
>      #define VCLKSET_DIV_V4H(n)  FIELD_PREP(VCLKSET_DIV_V4H_MASK, (n))
>                                  ^~~~~~~~~~
>     drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c:660:14: note: in expansion of macro 'VCLKSET_DIV_V4H'
>        vclkset |= VCLKSET_DIV_V4H(__ffs(setup_info.vclk_divider) - 1);
>                   ^~~~~~~~~~~~~~~

Hello Tomi, Laurent,

maybe it would be good to pick:

drm/rcar-du: dsi: Clean up VCLK divider calculation

that was posted about a month ago and fixes this exact warning ?