Hello Billy,

On Fri, Jul 09, 2021 at 05:40:45AM +0000, Billy Tsai wrote:
> On 2021/7/2, 10:32 PM, "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de> wrote:
>     > The multiplication can be up to:
> 
>     >	100000000 * (1 << 31) * (31 + 1) * (255 + 1)
> 
>     > right? This needs 71 bits and so might overflow a u64.
> 
> No, the multiplication can be up to:
> 
> Max(div_h) = 15
> Max(div_l) = 255
> Max(clk_period) = 255
> 1000000000 * (1 << 15) * (255 + 1) * (255 + 1) < 2^64 - 1
> it doesn't overflow a u64.

Ah, you're right. Please note this in a comment (not that you were
right, but that it doesn't overflow :-)

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |