Re: [PATCH][next] clk: imx: pll14xx: Fix potential integer overflow on multiplication

[Dan Carpenter]

On Mon, Oct 07, 2024 at 09:48:40AM +0100, Colin Ian King wrote:
> The calculation of fout is using int multiplication and assigning
> the result to a u64, this can potentially overflow if the int variable
> mdiv is too large. Fix this by making the 65536 a u64 value to ensure a
> u64 multiplication is being performed to avoid the overflow.
> 
> Fixes: 53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation")
> Signed-off-by: Colin Ian King <colin.i.king@xxxxxxxxx>

mdiv is always clamped in then 0-1023 range by one of these:

	mdiv = FIELD_GET(MDIV_MASK, pll_div_ctl0);
	mdiv = clamp(mdiv, 64, 1023);

so it can't overflow and the Fixes tag is unnecessary.

I think the reason why "fout" is declared as a u64 is because we were worried
that on 32 bit systems the "fout *=" operation could overflow.  That looks
reasonable to me.

regards,
dan carpenter