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

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Message-Id: <20250408175116.1770876-1-arnd@kernel.org>
Date: Tue,  8 Apr 2025 19:51:06 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: 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>,
	David 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>
Cc: Arnd Bergmann <arnd@...db.de>,
	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>,
	Douglas Anderson <dianders@...omium.org>,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: [PATCH] drm/bridge/synopsys: avoid field overflow warning

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 could not figure out if that overflow is actually possible or not,
but truncating the range to the maximum value avoids the warning and
probably can't hurt.

Fixes: 0d6d86253fef ("drm/bridge/synopsys: Add MIPI DSI2 host controller bridge")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi2.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi2.c
index 5fd7a459efdd..440b9a71012f 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi2.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi2.c
@@ -342,7 +342,7 @@ static void dw_mipi_dsi2_phy_ratio_cfg(struct dw_mipi_dsi2 *dsi2)
 	/*
 	 * SYS_RATIO_MAN_CFG = MIPI_DCPHY_HSCLK_Freq / MIPI_DCPHY_HSCLK_Freq
 	 */
-	tmp = DIV_ROUND_CLOSEST_ULL(phy_hsclk << 16, sys_clk);
+	tmp = min(DIV_ROUND_CLOSEST_ULL(phy_hsclk << 16, sys_clk), GENMASK(16, 0));
 	regmap_write(dsi2->regmap, DSI2_PHY_SYS_RATIO_MAN_CFG,
 		     PHY_SYS_RATIO(tmp));
 }
-- 
2.39.5