linux-kernel - [PATCH v3] drm/mediatek: Fix unused-but-set variable warning

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Date:   Thu, 30 Dec 2021 17:36:05 +0800
From:   Miles Chen <miles.chen@...iatek.com>
To:     Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Jie Qiu <jie.qiu@...iatek.com>,
        Junzhi Zhao <junzhi.zhao@...iatek.com>
CC:     Miles Chen <miles.chen@...iatek.com>,
        Zhiqiang Lin <zhiqiang.lin@...iatek.com>,
        CK Hu <ck.hu@...iatek.com>, <dri-devel@...ts.freedesktop.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <llvm@...ts.linux.dev>
Subject: [PATCH v3] drm/mediatek: Fix unused-but-set variable warning

clang reports a unused-but-set variable warning:
drivers/gpu/drm/mediatek/mtk_cec.c:85:6: warning: variable 'tmp' set but not used [-Wunused-but-set-variable]

In current implementation, mtk_cec_mask() writes val into target register
and ignores the mask. After talking to our hdmi experts, mtk_cec_mask()
should read a register, clean only mask bits, and update (val | mask) bits
to the register.

Fixes: 8f83f26891e1 ("drm/mediatek: Add HDMI support")

Cc: Zhiqiang Lin <zhiqiang.lin@...iatek.com>
Cc: CK Hu <ck.hu@...iatek.com>
Cc: Matthias Brugger <matthias.bgg@...il.com>

Signed-off-by: Miles Chen <miles.chen@...iatek.com>

---

Change since v1:
add Fixes tag

Change since v2:
add explanation of mtk_cec_mask()

Change-Id: Iec6402b0532942f4d0e8bc56817eb87b95c03fad
---
 drivers/gpu/drm/mediatek/mtk_cec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_cec.c b/drivers/gpu/drm/mediatek/mtk_cec.c
index e9cef5c0c8f7..cdfa648910b2 100644
--- a/drivers/gpu/drm/mediatek/mtk_cec.c
+++ b/drivers/gpu/drm/mediatek/mtk_cec.c
@@ -85,7 +85,7 @@ static void mtk_cec_mask(struct mtk_cec *cec, unsigned int offset,
 	u32 tmp = readl(cec->regs + offset) & ~mask;
 
 	tmp |= val & mask;
-	writel(val, cec->regs + offset);
+	writel(tmp, cec->regs + offset);
 }
 
 void mtk_cec_set_hpd_event(struct device *dev,
-- 
2.18.0