On 2023-09-01 13:06:40, Devi Priya wrote:
> If the parent clock rate is greater than unsigned long max/2 then
> integer overflow happens when calculating the clock rate on 32-bit systems.
> As RCG2 uses half integer dividers, the clock rate is first being
> multiplied by 2 which will overflow the unsigned long max value.
> Hence, replace the common pattern of doing 64-bit multiplication
Wasn't it doing 32-bit multiplication on 32-bit systems? Glad to see the u64
mul and div cleaned up in the if (mode) block either way though.
> and then a do_div() call with simpler mult_frac call.
mul_frac()
>
> Fixes: bcd61c0f535a ("clk: qcom: Add support for root clock generators (RCGs)")
> Signed-off-by: Devi Priya <quic_devipriy@xxxxxxxxxxx>
> ---
> Changes in V2:
> - Replaced 64-bit multiplication & a do_div call with mult_frac
> call as suggested by Marijn Suijten.
Don't forget to add reviewers to CC on followup revisions :)
Reviewed-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>
> - Updated the subject title
> - Added Fixes tag
> - Did not pick up the R-b tag due to the above changes.
>
> drivers/clk/qcom/clk-rcg2.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
> index a42f661550ca..f64d69164547 100644
> --- a/drivers/clk/qcom/clk-rcg2.c
> +++ b/drivers/clk/qcom/clk-rcg2.c
> @@ -159,15 +159,11 @@ static unsigned long
> calc_rate(unsigned long rate, u32 m, u32 n, u32 mode, u32 hid_div)
> {
> if (hid_div) {
> - rate *= 2;
> - rate /= hid_div + 1;
> + rate = mult_frac(rate, 2, hid_div + 1);
> }
>
> if (mode) {
> - u64 tmp = rate;
> - tmp *= m;
> - do_div(tmp, n);
> - rate = tmp;
> + rate = mult_frac(rate, m, n);
> }
>
> return rate;
> --
> 2.34.1
>
