Re: [lvc-project] [PATCH v3] clk: mvebu: Prevent division by zero in clk_double_div_recalc_rate()

[Fedor Pchelkin]

Hi Andrew,

On Tue, 08. Oct 23:58, Andrew Lunn wrote:
> On Mon, Oct 07, 2024 at 03:56:29PM -0700, Stephen Boyd wrote:
> > Quoting Alexandra Diupina (2024-09-24 06:14:44)
> > > >> diff --git a/drivers/clk/mvebu/armada-37xx-periph.c b/drivers/clk/mvebu/armada-37xx-periph.c
> > > >> index 8701a58a5804..b32c6d4d7ee5 100644
> > > >> --- a/drivers/clk/mvebu/armada-37xx-periph.c
> > > >> +++ b/drivers/clk/mvebu/armada-37xx-periph.c
> > > >> @@ -343,7 +343,12 @@ static unsigned long clk_double_div_recalc_rate(struct clk_hw *hw,
> > > >>          div = get_div(double_div->reg1, double_div->shift1);
> > > >>          div *= get_div(double_div->reg2, double_div->shift2);
> > > >>   
> > > >> -       return DIV_ROUND_UP_ULL((u64)parent_rate, div);
> > > >> +       if (!div) {
> > > >> +               pr_err("Can't recalculate the rate of clock %s\n", hw->init->name);
> > > > hw->init is set to NULL after registration (see clk_register() code). If
> > > > div is 0 what does the hardware do?
> > > 
> > > Thanks for noticing the error. Yes, hw->init is set to zero,
> > > I will replace that code with clk_hw_get_name(hw).
> > > If the value of div is 0, should I return 0 as stated in the
> > > comment for .recalc_rate (in struct clk_ops) or should I
> > > return parent_rate as in some other similar rate recalculation
> > > functions (in some other drivers)?
> > 
> > It depends on what the hardware does. Does the hardware pass on the
> > parent rate if the divider is zero? If so, then return parent_rate. Or
> > does it turn off completely? If so, return zero.
> 
> I don't think anybody knows what the hardware does in this
> condition. I also suspect it has never happened, or if it has, nobody
> has complained.
> 
> I would say, let is divide by 0, so there is an obvious kernel stack
> trace and hopefully a report of the issue. It can then be investigated
> in a way we can then find out what the hardware actually is doing.

Is it worth adding some kind of WARN assertions? Or actually just leave it
for now as is?