linux-kernel - Re: [PATCH] drm/bridge/synopsys: avoid field overflow warning

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Message-ID: <20250507090650.GKaBsiqpQ9jMaWHgx1@fat_crate.local>
Date: Wed, 7 May 2025 11:06:50 +0200
From: Borislav Petkov <bp@...en8.de>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>, Andrzej Hajda <andrzej.hajda@...el.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Robert Foss <rfoss@...nel.org>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Dave Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Nathan Chancellor <nathan@...nel.org>,
	Heiko Stuebner <heiko.stuebner@...rry.de>,
	Andy Yan <andy.yan@...k-chips.com>,
	"laurent.pinchart" <Laurent.pinchart@...asonboard.com>,
	Jonas Karlman <jonas@...boo.se>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Dmitry Baryshkov <lumag@...nel.org>,
	Doug Anderson <dianders@...omium.org>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: Re: [PATCH] drm/bridge/synopsys: avoid field overflow warning

On Thu, Apr 10, 2025 at 02:36:45PM +0200, Arnd Bergmann wrote:
> On Wed, Apr 9, 2025, at 09:07, Arnd Bergmann wrote:
> > On Tue, Apr 8, 2025, at 19:51, Arnd Bergmann wrote:
> >> From: Arnd Bergmann <arnd@...db.de>
> >>
> >> clang-16 and earlier complain about what it thinks might be an out of
> >> range number:
> >>
> >> drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi2.c:348:8: error: call to 
> >> __compiletime_assert_579 declared with 'error' attribute: FIELD_PREP: 
> >> value too large for the field
> >>                      PHY_SYS_RATIO(tmp));
> >>                      ^
> >> drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi2.c:90:27: note: expanded 
> >> from macro 'PHY_SYS_RATIO'
> >>  #define PHY_SYS_RATIO(x)                FIELD_PREP(GENMASK(16, 0), x)
> >>
> >
> > I still see the same build failure in some other configurations even
> > with this patch. Please disregard this version, I'll try to come
> > up with a better one.
> 
> I couldn't come up with anything that actually worked, other than
> the hack below, which just works around the compiletime error
> in FIELD_PREP(), but doesn't look like a proper fix.
> 
> If anyone else has any ideas, I can test their patch.
> 
>        Arnd
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi2.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi2.c
> index c76f5f2e74d1..8ba528462ede 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi2.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi2.c
> @@ -344,7 +344,7 @@ static void dw_mipi_dsi2_phy_ratio_cfg(struct dw_mipi_dsi2 *dsi2)
>          */
>         tmp = DIV_ROUND_CLOSEST_ULL(phy_hsclk << 16, sys_clk);
>         regmap_write(dsi2->regmap, DSI2_PHY_SYS_RATIO_MAN_CFG,
> -                    PHY_SYS_RATIO(tmp));
> +                    PHY_SYS_RATIO(tmp & GENMASK(16, 0)));
>  }
>  
>  static void dw_mipi_dsi2_lp2hs_or_hs2lp_cfg(struct dw_mipi_dsi2 *dsi2)

I see this too in my randconfigs.

Attaching .config in case someone wants to repro and perhaps even fix it.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

View attachment "00-50-44-randconfig-x86_64-18371.cfg" of type "text/plain" (147178 bytes)