linux-kernel - [PATCH] drm/mediatek: mtk_hdmi_v2: Fix return type of mtk_hdmi_v2_tmds_char_rate

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Message-Id: <20251125-drm-mediatek-hdmi-v2-wifpts-v1-1-a6c7582cf69a@kernel.org>
Date: Tue, 25 Nov 2025 15:14:23 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Chun-Kuang Hu <chunkuang.hu@...nel.org>, 
 Philipp Zabel <p.zabel@...gutronix.de>
Cc: David Airlie <airlied@...il.com>, 
 Matthias Brugger <matthias.bgg@...il.com>, 
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
 Louis-Alexis Eyraud <louisalexis.eyraud@...labora.com>, 
 CK Hu <ck.hu@...iatek.com>, dri-devel@...ts.freedesktop.org, 
 linux-mediatek@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org, 
 llvm@...ts.linux.dev, patches@...ts.linux.dev, linux-kernel@...r.kernel.org, 
 Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] drm/mediatek: mtk_hdmi_v2: Fix return type of
 mtk_hdmi_v2_tmds_char_rate_valid()

When building with -Wincompatible-function-pointer-types-strict, a
warning designed to catch kernel control flow integrity (kCFI) issues at
build time, there is an instance in the new HDMI v2 drm/mediatek code:

  drivers/gpu/drm/mediatek/mtk_hdmi_v2.c:1331:31: error: incompatible function pointer types initializing 'enum drm_mode_status (*)(const struct drm_bridge *, const struct drm_display_mode *, unsigned long long)' with an expression of type 'int (const struct drm_bridge *, const struct drm_display_mode *, unsigned long long)' [-Werror,-Wincompatible-function-pointer-types-strict]
   1331 |         .hdmi_tmds_char_rate_valid = mtk_hdmi_v2_hdmi_tmds_char_rate_valid,
        |                                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

While 'int' and 'enum drm_mode_status' are ABI compatible, hence no
regular warning from -Wincompatible-function-pointer-types, the mismatch
will trigger a kCFI violation when mtk_hdmi_v2_tmds_char_rate_valid() is
called indirectly.

Update the return type of mtk_hdmi_v2_tmds_char_rate_valid() to be 'enum
drm_mode_status' to clear up the warning and kCFI violation.

Fixes: 8d0f79886273 ("drm/mediatek: Introduce HDMI/DDC v2 for MT8195/MT8188")
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 drivers/gpu/drm/mediatek/mtk_hdmi_v2.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_hdmi_v2.c b/drivers/gpu/drm/mediatek/mtk_hdmi_v2.c
index c272e1e74b7d..454b8b93b834 100644
--- a/drivers/gpu/drm/mediatek/mtk_hdmi_v2.c
+++ b/drivers/gpu/drm/mediatek/mtk_hdmi_v2.c
@@ -1120,9 +1120,10 @@ static void mtk_hdmi_v2_hpd_disable(struct drm_bridge *bridge)
 	mtk_hdmi_v2_disable(hdmi);
 }
 
-static int mtk_hdmi_v2_hdmi_tmds_char_rate_valid(const struct drm_bridge *bridge,
-						 const struct drm_display_mode *mode,
-						 unsigned long long tmds_rate)
+static enum drm_mode_status
+mtk_hdmi_v2_hdmi_tmds_char_rate_valid(const struct drm_bridge *bridge,
+				      const struct drm_display_mode *mode,
+				      unsigned long long tmds_rate)
 {
 	if (mode->clock < MTK_HDMI_V2_CLOCK_MIN)
 		return MODE_CLOCK_LOW;

---
base-commit: a846505a193d7492ad3531e33cacfca31e4bcdd1
change-id: 20251125-drm-mediatek-hdmi-v2-wifpts-d67b55175609

Best regards,
--  
Nathan Chancellor <nathan@...nel.org>