linux-kernel - [PATCH v2] i2c: altera: Fix potential integer overflow

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Message-ID: <20200211144704.GA6461@embeddedor>
Date:   Tue, 11 Feb 2020 08:47:04 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Thor Thayer <thor.thayer@...ux.intel.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        David Laight <David.Laight@...LAB.COM>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH v2] i2c: altera: Fix potential integer overflow

Factor out 100 from the equation and do 32-bit arithmetic (3 * clk_mhz / 10)
instead of 64-bit.

Notice that clk_mhz is MHz, so the multiplication will never wrap 32 bits
and there is no need for div_u64().

Addresses-Coverity: 1458369 ("Unintentional integer overflow")
Fixes: 0560ad576268 ("i2c: altera: Add Altera I2C Controller driver")
Suggested-by: David Laight <David.Laight@...LAB.COM>
Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
Changes in v2:
 - Update subject and changelog text.
 - Avoid the need for 64-bit arithmetic at all.

 drivers/i2c/busses/i2c-altera.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-altera.c b/drivers/i2c/busses/i2c-altera.c
index 5255d3755411..1de23b4f3809 100644
--- a/drivers/i2c/busses/i2c-altera.c
+++ b/drivers/i2c/busses/i2c-altera.c
@@ -171,7 +171,7 @@ static void altr_i2c_init(struct altr_i2c_dev *idev)
 	/* SCL Low Time */
 	writel(t_low, idev->base + ALTR_I2C_SCL_LOW);
 	/* SDA Hold Time, 300ns */
-	writel(div_u64(300 * clk_mhz, 1000), idev->base + ALTR_I2C_SDA_HOLD);
+	writel(3 * clk_mhz / 10, idev->base + ALTR_I2C_SDA_HOLD);
 
 	/* Mask all master interrupt bits */
 	altr_i2c_int_enable(idev, ALTR_I2C_ALL_IRQ, false);
-- 
2.25.0