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Message-ID: <20251230103058.GE6598@pendragon.ideasonboard.com>
Date: Tue, 30 Dec 2025 12:30:58 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Marek Vasut <marek.vasut@...lbox.org>
Cc: kernel test robot <lkp@...el.com>,
Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
"open list:MEDIA DRIVERS FOR RENESAS - FCP" <linux-renesas-soc@...r.kernel.org>
Subject: 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
On Tue, Dec 30, 2025 at 03:47:17AM +0100, Marek Vasut wrote:
> 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@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/20251205/202512051834.bESvhDiG-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/202512051834.bESvhDiG-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.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'
> > vclkset |= VCLKSET_DIV_V4H(__ffs(setup_info.vclk_divider) - 1);
> > ^~~~~~~~~~~~~~~
> I don't think this condition can occur.
>
> 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.
> diff --git a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
> b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
> index 4ef2e3c129ed7..20e2a4cae5b86 100644
> --- a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
> +++ b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
> @@ -84,7 +84,6 @@ struct dsi_setup_info {
> unsigned long fout;
> u16 m;
> u16 n;
> - u16 vclk_divider;
> const struct dsi_clk_config *clkset;
> };
>
> @@ -338,7 +337,8 @@ rcar_mipi_dsi_post_init_phtw_v4h(struct
> rcar_mipi_dsi *dsi,
> static void rcar_mipi_dsi_pll_calc(struct rcar_mipi_dsi *dsi,
> unsigned long fin_rate,
> unsigned long fout_target,
> - struct dsi_setup_info *setup_info)
> + struct dsi_setup_info *setup_info,
> + u16 vclk_divider)
> {
> unsigned int best_err = -1;
> const struct rcar_mipi_dsi_device_info *info = dsi->info;
> @@ -391,6 +391,7 @@ static void rcar_mipi_dsi_parameters_calc(struct
> rcar_mipi_dsi *dsi,
> unsigned long fin_rate;
> unsigned int i;
> unsigned int err;
> + u16 vclk_divider;
>
> /*
> * Calculate Fout = dot clock * ColorDepth / (2 * Lane Count)
> @@ -415,15 +416,15 @@ static void rcar_mipi_dsi_parameters_calc(struct
> rcar_mipi_dsi *dsi,
> switch (dsi->info->model) {
> case RCAR_DSI_V3U:
> default:
> - setup_info->vclk_divider = 1 << ((clk_cfg->vco_cntrl >> 4) & 0x3);
> + vclk_divider = 1 << ((clk_cfg->vco_cntrl >> 4) & 0x3);
> break;
>
> case RCAR_DSI_V4H:
> - setup_info->vclk_divider = 1 << (((clk_cfg->vco_cntrl >> 3) & 0x7) + 1);
> + vclk_divider = 1 << (((clk_cfg->vco_cntrl >> 3) & 0x7) + 1);
> break;
> }
>
> - rcar_mipi_dsi_pll_calc(dsi, fin_rate, fout_target, setup_info);
> + rcar_mipi_dsi_pll_calc(dsi, fin_rate, fout_target, setup_info, vclk_divider);
>
> /* Find hsfreqrange */
> setup_info->hsfreq = setup_info->fout * 2;
> @@ -439,7 +440,7 @@ static void rcar_mipi_dsi_parameters_calc(struct rcar_mipi_dsi *dsi,
> dev_dbg(dsi->dev,
> "Fout = %u * %lu / (%u * %u * %u) = %lu (target %lu Hz, error %d.%02u%%)\n",
> setup_info->m, fin_rate, dsi->info->n_mul, setup_info->n,
> - setup_info->vclk_divider, setup_info->fout, fout_target,
> + vclk_divider, setup_info->fout, fout_target,
> err / 100, err % 100);
>
> dev_dbg(dsi->dev,
> @@ -653,11 +654,11 @@ static int rcar_mipi_dsi_startup(struct rcar_mipi_dsi *dsi,
> switch (dsi->info->model) {
> case RCAR_DSI_V3U:
> default:
> - vclkset |= VCLKSET_DIV_V3U(__ffs(setup_info.vclk_divider));
> + vclkset |= VCLKSET_DIV_V3U((clk_cfg->vco_cntrl >> 4) & 0x3);
> break;
>
> case RCAR_DSI_V4H:
> - vclkset |= VCLKSET_DIV_V4H(__ffs(setup_info.vclk_divider) - 1);
> + vclkset |= VCLKSET_DIV_V4H((clk_cfg->vco_cntrl >> 3) & 0x7);
> break;
> }
Laurent Pinchart
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