Re: include/linux/compiler_types.h:597:38: error: call to '__compiletime_assert_437' declared with attribute error: FIELD_PREP: value too large for the field
From: Marek Vasut
Date: Wed Dec 31 2025 - 10:06:49 EST
On 12/30/25 11:30 AM, Laurent Pinchart wrote:
On Tue, Dec 30, 2025 at 03:47:17AM +0100, Marek Vasut wrote:I believe the following rework should address the duplication concern too:
On 12/5/25 11:16 AM, kernel test robot wrote:
tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head: 2061f18ad76ecaddf8ed17df81b8611ea88dbddd
commit: 4f716a1db661cfb31502a0a6d7e62c06daf2e603 drm/rcar-du: dsi: Convert register bitfields to GENMASK() macro
date: 5 weeks ago
config: arc-randconfig-001-20251205 (https://download.01.org/0day-ci/archive/20251205/202512051834.bESvhDiG-lkp@xxxxxxxxx/config)
compiler: arc-linux-gcc (GCC) 8.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251205/202512051834.bESvhDiG-lkp@xxxxxxxxx/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@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512051834.bESvhDiG-lkp@xxxxxxxxx/
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.4':
include/linux/compiler_types.h:597:38: error: call to '__compiletime_assert_437' declared with attribute error: FIELD_PREP: value too large for the field
[...]
rcar_mipi_dsi.c:660:14: note: in expansion of macro 'VCLKSET_DIV_V4H'I don't think this condition can occur.
vclkset |= VCLKSET_DIV_V4H(__ffs(setup_info.vclk_divider) - 1);
^~~~~~~~~~~~~~~
In drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c :
- rcar_mipi_dsi_startup() calls rcar_mipi_dsi_parameters_calc() which is
the only site that assigns setup_info.vclk_divider this way:
415 switch (dsi->info->model) {
416 case RCAR_DSI_V3U:
417 default:
418 setup_info->vclk_divider = 1 << ((clk_cfg->vco_cntrl >> 4) & 0x3);
419 break;
420
421 case RCAR_DSI_V4H:
422 setup_info->vclk_divider = 1 << (((clk_cfg->vco_cntrl >> 3) & 0x7) + 1);
423 break;
424 }
In case of V3U, vclk_divider is 1 << (0..3) .
In case of V4H, vclk_divider is 1 << (1..8) .
In drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c :
- rcar_mipi_dsi_startup() later contains the offending code:
653 switch (dsi->info->model) {
654 case RCAR_DSI_V3U:
655 default:
656 vclkset |= VCLKSET_DIV_V3U(__ffs(setup_info.vclk_divider));
657 break;
658
659 case RCAR_DSI_V4H:
660 vclkset |= VCLKSET_DIV_V4H(__ffs(setup_info.vclk_divider) - 1);
661 break;
662 }
This does the reverse of the code that assigned the value above, so:
In case of V3U, field value is (0..3) .
In case of V4H, field value is (0..7) .
Finally in drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi_regs.h :
256 #define VCLKSET_DIV_V3U_MASK GENMASK_U32(5, 4)
257 #define VCLKSET_DIV_V3U(n)
FIELD_PREP(VCLKSET_DIV_V3U_MASK, (n))
258 #define VCLKSET_DIV_V4H_MASK GENMASK_U32(6, 4)
259 #define VCLKSET_DIV_V4H(n)
FIELD_PREP(VCLKSET_DIV_V4H_MASK, (n))
The masks fit exactly. For V3U the mask is 2-bit, or V4H the mask is 3-bit .
...
I can however rewrite the code in this way, which should also mitigate
this warning. Do you think this makes the code any better ?
The datasheet says that the VCLKSET.DIV field "should be same as the
CLOCKSET2.vco_cntrl[5:3]". The change below makes this explicit, which
may not be a bad thing, even if it duplicates the small calculation.
https://lore.kernel.org/dri-devel/20251231145712.60816-1-marek.vasut+renesas@xxxxxxxxxxx/