Messages in this thread | | | From | Heiko Stübner <> | Subject | Re: [PATCH] clk: fractional-divider: cast parent_rate to u64 before multiplying | Date | Wed, 10 Sep 2014 17:54:16 +0200 |
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Hi Mike,
Am Dienstag, 2. September 2014, 09:33:21 schrieb Heiko Stübner: > Am Montag, 1. September 2014, 17:26:29 schrieb Mike Turquette: > > Quoting Heiko Stübner (2014-08-28 03:46:10) > > > > > On 32bit architectures, like ARM calculating the fractional rate will > > > do the multiplication before converting the value to u64 when it gets > > > assigned to ret, which can produce overflows. > > > > > > The error in question happened with a parent_rate of 386MHz, m = 3000, > > > n = 60000, which resulted in a wrong rate value of 15812Hz. > > > > > > Therefore cast parent_rate to u64 to make sure the multiplication > > > happens in a 64bit space and produces the correct 192MHz in the example. > > > > > > Signed-off-by: Heiko Stuebner <heiko@sntech.de> > > > > Looks good to me. Have you observed this issue using the vanilla > > kernel.org sources or on a downstream tree? I'm trying to decide if I > > should take this into clk-fixes or clk-next. > > > > If this doesn't happen in practice on any merged platform then I'll take > > it for 3.18. > > It happens on the Rockchip platform with the newly added fractional branches > you just applied ... so it doesn't look like anybody else is affected right > now.
will you take this one into clk-next?
Thanks Heiko
> > > Heiko > > > Regards, > > Mike > > > > > --- > > > > > > drivers/clk/clk-fractional-divider.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/drivers/clk/clk-fractional-divider.c > > > b/drivers/clk/clk-fractional-divider.c index ede685c..82a59d0 100644 > > > --- a/drivers/clk/clk-fractional-divider.c > > > +++ b/drivers/clk/clk-fractional-divider.c > > > @@ -36,7 +36,7 @@ static unsigned long clk_fd_recalc_rate(struct clk_hw > > > *hw,> > > > > > > m = (val & fd->mmask) >> fd->mshift; > > > n = (val & fd->nmask) >> fd->nshift; > > > > > > - ret = parent_rate * m; > > > + ret = (u64)parent_rate * m; > > > > > > do_div(ret, n); > > > > > > return ret;
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