linux-kernel - Re: [PATCH v3 1/3] clk: k210: remove an implicit 64-bit division

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Date:   Mon, 06 Mar 2023 14:37:22 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Conor Dooley <conor@...nel.org>
Cc:     Jesse Taube <mr.bossman075@...il.com>,
        linux-riscv@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, Yimin Gu <ustcymgu@...il.com>,
        Damien Le Moal <damien.lemoal@....com>,
        Michael Turquette <mturquette@...libre.com>,
        Waldemar Brodkorb <wbx@...nadk.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v3 1/3] clk: k210: remove an implicit 64-bit division

Quoting Conor Dooley (2023-03-06 14:35:01)
> On Mon, Mar 06, 2023 at 02:31:00PM -0800, Stephen Boyd wrote:
> > Quoting Jesse Taube (2023-02-28 16:26:55)
> > > diff --git a/drivers/clk/clk-k210.c b/drivers/clk/clk-k210.c
> > > index 67a7cb3503c3..4eed667eddaf 100644
> > > --- a/drivers/clk/clk-k210.c
> > > +++ b/drivers/clk/clk-k210.c
> > > @@ -495,7 +495,7 @@ static unsigned long k210_pll_get_rate(struct clk_hw *hw,
> > >         f = FIELD_GET(K210_PLL_CLKF, reg) + 1;
> > >         od = FIELD_GET(K210_PLL_CLKOD, reg) + 1;
> > >  
> > > -       return (u64)parent_rate * f / (r * od);
> > > +       return div_u64((u64)parent_rate * f, r * od);
> > 
> > The equation 'r * od' can't overflow 32-bits, right?
> 
> Yah, I checked that when writing the patch. They're 4-bit fields:

Awesome