linux-kernel - [PATCH v2] drm:sprd: Correct left shift operator evaluating constant expression

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Message-Id: <20241108-coverity1511468wrongoperator-v2-1-72bc73d8691f@gmail.com>
Date: Fri, 08 Nov 2024 17:11:25 +0000
From: Karan Sanghavi <karansanghvi98@...il.com>
To: 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>, 
 Orson Zhai <orsonzhai@...il.com>, 
 Baolin Wang <baolin.wang@...ux.alibaba.com>, 
 Chunyan Zhang <zhang.lyra@...il.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 Shuah Khan <skhan@...uxfoundation.org>, 
 Karan Sanghavi <karansanghvi98@...il.com>
Subject: [PATCH v2] drm:sprd: Correct left shift operator evaluating
 constant expression

The left shift operation followed by a mask with 0xf will
always result in 0. To correctly evaluate the expression for
the bitwise OR operation, use a right shift instead.

Reported by Coverity Scan CID: 1511468

Fixes: 1c66496b1391 ("drm/sprd: add Unisoc's drm mipi dsi&dphy driver")

Reviewed-by: Chunyan Zhang <zhang.lyra@...il.com>
Signed-off-by: Karan Sanghavi <karansanghvi98@...il.com>
---
Coverity Scan Message:
CID 1511468: (#1 of 1): Wrong operator used (CONSTANT_EXPRESSION_RESULT)
operator_confusion: (pll->kint << 4) & 15 is always 0 regardless of the 
values of its operands. This occurs as the bitwise second operand of "|"
---
Changes in v2:
- Added the fixes tag
- Link to v1: https://lore.kernel.org/r/20241105-coverity1511468wrongoperator-v1-1-06c7513c3efc@gmail.com
---
 drivers/gpu/drm/sprd/megacores_pll.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/sprd/megacores_pll.c b/drivers/gpu/drm/sprd/megacores_pll.c
index 3091dfdc11e3..43c10a5fc441 100644
--- a/drivers/gpu/drm/sprd/megacores_pll.c
+++ b/drivers/gpu/drm/sprd/megacores_pll.c
@@ -94,7 +94,7 @@ static void dphy_set_pll_reg(struct dphy_pll *pll, struct regmap *regmap)
 	reg_val[3] = pll->vco_band | (pll->sdm_en << 1) | (pll->refin << 2);
 	reg_val[4] = pll->kint >> 12;
 	reg_val[5] = pll->kint >> 4;
-	reg_val[6] = pll->out_sel | ((pll->kint << 4) & 0xf);
+	reg_val[6] = pll->out_sel | ((pll->kint >> 4) & 0xf);
 	reg_val[7] = 1 << 4;
 	reg_val[8] = pll->det_delay;
 

---
base-commit: 81983758430957d9a5cb3333fe324fd70cf63e7e
change-id: 20241105-coverity1511468wrongoperator-20130bcd4240

Best regards,
-- 
Karan Sanghavi <karansanghvi98@...il.com>