From: Gustavo A. R. Silva
> Sent: 10 February 2020 19:27
>
> Add suffix ULL to constant 300 in order to avoid a potential integer
> overflow and give the compiler complete information about the proper
> arithmetic to use. Notice that this constant is being used in a context
> that expects an expression of type u64, but it's currently evaluated
> using 32-bit arithmetic.
>
> Addresses-Coverity: 1458369 ("Unintentional integer overflow")
> Fixes: 0560ad576268 ("i2c: altera: Add Altera I2C Controller driver")
> Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> ---
> drivers/i2c/busses/i2c-altera.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/i2c/busses/i2c-altera.c b/drivers/i2c/busses/i2c-altera.c
> index 5255d3755411..526f453f0ff7 100644
> --- a/drivers/i2c/busses/i2c-altera.c
> +++ b/drivers/i2c/busses/i2c-altera.c
> @@ -171,7 +171,8 @@ 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(div_u64(300ULL * clk_mhz, 1000),
> + idev->base + ALTR_I2C_SDA_HOLD);
Why not factor out the 100?
It may then be you can do 32bit arithmetic (3 * clk_mhz / 10).
If clk_mhz is MHz (not mHz) then the sum will never wrap 32 bits.
David
-
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