Re: [linux-next:master 2742/4710] drivers/clk/clk-versaclock3.c:404:2-8: WARNING: do_div() does a 64-by-32 division, please consider using div64_ul instead. (fwd)

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Biju,

On Thu, Jul 27, 2023 at 11:19 AM Biju Das <biju.das.jz@bp.renesas.com> wrote:
> > versaclock3.c:404:2-8: WARNING: do_div() does a 64-by-32 division, please
> > consider using div64_ul instead. (fwd)
> >
> > On Thu, 27 Jul 2023, Biju Das wrote:
> > > The reproduce link is not working for me.
> > >
> > > Can you please provide instruction to reproduce this issue?
> >
> > I don't think it's intended to be reproduced.  The issue is just that a
> > long value is being passed to an integer that is 32 bit.  If the long
> > value will never be very big, then you can just ignore the warning.
>
> The rate values are well below max 32 bit, 4294967296. So I guess, it is ok.

The type of the parent_rate in/output parameter of clk_ops.round_rate()
is unsigned long.  Hence you should use div64_ul().

> > > > versaclock3.c:404:2-8: WARNING: do_div() does a 64-by-32 division,
> > > > please consider using div64_ul instead. (fwd)
> > > >
> > > >
> > > >
> > > > ---------- Forwarded message ----------
> > > > Date: Thu, 27 Jul 2023 08:50:37 +0800
> > > > From: kernel test robot <lkp@intel.com>
> > > > To: oe-kbuild@lists.linux.dev
> > > > Cc: lkp@intel.com, Julia Lawall <julia.lawall@inria.fr>
> > > > Subject: [linux-next:master 2742/4710] drivers/clk/clk-
> > > > versaclock3.c:404:2-8:
> > > >     WARNING: do_div() does a 64-by-32 division,
> > > >     please consider using div64_ul instead.
> > > >
> > > > BCC: lkp@intel.com
> > > > CC: oe-kbuild-all@lists.linux.dev
> > > > CC: Linux Memory Management List <linux-mm@kvack.org>
> > > > TO: Biju Das <biju.das.jz@bp.renesas.com>
> > > > CC: Stephen Boyd <sboyd@kernel.org>
> > > >
> > > > tree:
> > > >
> > > > If you fix the issue in a separate patch/commit (i.e. not just a new
> > > > version of the same patch/commit), kindly add following tags
> > > > | Reported-by: kernel test robot <lkp@intel.com>
> > > > | Reported-by: Julia Lawall <julia.lawall@inria.fr>
> > > > | Closes:
> > > %2BsY49B78%3D&reserved=0
> > > >
> > > > cocci warnings: (new ones prefixed by >>)
> > > > >> drivers/clk/clk-versaclock3.c:404:2-8: WARNING: do_div() does a
> > > > >> 64-
> > > > by-32 division, please consider using div64_ul instead.
> > > >
> > > > vim +404 drivers/clk/clk-versaclock3.c
> > > >
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  382
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  383  static long
> > > > vc3_pll_round_rate(struct clk_hw *hw, unsigned long rate,
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  384
> > unsigned
> > > > long *parent_rate)
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  385  {
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  386   struct vc3_hw_data *vc3 =
> > > > container_of(hw, struct vc3_hw_data, hw);
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  387   const struct vc3_pll_data
> > *pll
> > > > = vc3->data;
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  388   u64 div_frc;
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  389
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  390   if (rate < pll->vco_min)
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  391           rate = pll->vco_min;
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  392   if (rate > pll->vco_max)
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  393           rate = pll->vco_max;
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  394
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  395   vc3->div_int = rate /
> > > > *parent_rate;
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  396
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  397   if (pll->num == VC3_PLL2)
> > {
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  398           if (vc3->div_int >
> > 0x7ff)
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  399                   rate =
> > *parent_rate
> > > > * 0x7ff;
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  400
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  401           /* Determine best
> > > > fractional part, which is 16 bit wide */
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  402           div_frc = rate %
> > > > *parent_rate;
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  403           div_frc *= BIT(16) -
> > 1;
> > > > 6e9aff555db7b6 Biju Das 2023-07-05 @404           do_div(div_frc,
> > > > *parent_rate);
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  405
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  406           vc3->div_frc =
> > > > (u32)div_frc;
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  407           rate = (*parent_rate
> > *
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  408                   (vc3->div_int
> > *
> > > > VC3_2_POW_16 + div_frc) / VC3_2_POW_16);
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  409   } else {
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  410           rate = *parent_rate
> > *
> > > > vc3->div_int;
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  411   }
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  412
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  413   return rate;
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  414  }
> > > > 6e9aff555db7b6 Biju Das 2023-07-05  415
> > > >
> > > > --
> > > > 0-DAY CI Kernel Test Service
> > >



-- 
Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds