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From:   Tim Gardner <tim.gardner@canonical.com>
To:     dri-devel@lists.freedesktop.org
Cc:     tim.gardner@canonical.com, Rob Clark <robdclark@gmail.com>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Abhinav Kumar <abhinavk@codeaurora.org>,
        linux-arm-msm@vger.kernel.org, freedreno@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] drm/msm/dsi: prevent unintentional integer overflow in dsi_pll_28nm_clk_recalc_rate()
Date:   Wed, 29 Sep 2021 11:51:34 -0600
Message-Id: <20210929175134.15808-1-tim.gardner@canonical.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Coverity warns of an unintentional integer overflow

CID 120715 (#1 of 1): Unintentional integer overflow (OVERFLOW_BEFORE_WIDEN)
overflow_before_widen: Potentially overflowing expression ref_clk * sdm_byp_div
  with type unsigned int (32 bits, unsigned) is evaluated using 32-bit arithmetic,
  and then used in a context that expects an expression of type unsigned long
  (64 bits, unsigned).
To avoid overflow, cast either ref_clk or sdm_byp_div to type unsigned long.
263                vco_rate = ref_clk * sdm_byp_div;

Fix this and another possible overflow by casting ref_clk to unsigned long.

Cc: Rob Clark <robdclark@gmail.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: Abhinav Kumar <abhinavk@codeaurora.org>
Cc: linux-arm-msm@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: freedreno@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---
 drivers/gpu/drm/msm/dsi/phy/dsi_phy_28nm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/msm/dsi/phy/dsi_phy_28nm.c b/drivers/gpu/drm/msm/dsi/phy/dsi_phy_28nm.c
index 2da673a2add6..cfe4b30eb96d 100644
--- a/drivers/gpu/drm/msm/dsi/phy/dsi_phy_28nm.c
+++ b/drivers/gpu/drm/msm/dsi/phy/dsi_phy_28nm.c
@@ -260,7 +260,7 @@ static unsigned long dsi_pll_28nm_clk_recalc_rate(struct clk_hw *hw,
 		sdm_byp_div = FIELD(
 				dsi_phy_read(base + REG_DSI_28nm_PHY_PLL_SDM_CFG0),
 				DSI_28nm_PHY_PLL_SDM_CFG0_BYP_DIV) + 1;
-		vco_rate = ref_clk * sdm_byp_div;
+		vco_rate = (unsigned long)ref_clk * sdm_byp_div;
 	} else {
 		/* sdm mode */
 		sdm_dc_off = FIELD(
@@ -274,7 +274,7 @@ static unsigned long dsi_pll_28nm_clk_recalc_rate(struct clk_hw *hw,
 		sdm_freq_seed = (sdm3 << 8) | sdm2;
 		DBG("sdm_freq_seed = %d", sdm_freq_seed);
 
-		vco_rate = (ref_clk * (sdm_dc_off + 1)) +
+		vco_rate = ((unsigned long)ref_clk * (sdm_dc_off + 1)) +
 			mult_frac(ref_clk, sdm_freq_seed, BIT(16));
 		DBG("vco rate = %lu", vco_rate);
 	}
-- 
2.33.0