linux-kernel - Re: [PATCH v3] clk: mvebu: Prevent division by zero in clk_double_div_recalc

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Message-ID: <c2250a7cd0e2af5077ade91279567c3b.sboyd@kernel.org>
Date: Mon, 07 Oct 2024 15:56:29 -0700
From: Stephen Boyd <sboyd@...nel.org>
To: Alexandra Diupina <adiupina@...ralinux.ru>, Andrew Lunn <andrew@...n.ch>
Cc: Gregory Clement <gregory.clement@...tlin.com>, Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>, Michael Turquette <mturquette@...libre.com>, linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org
Subject: Re: [PATCH v3] clk: mvebu: Prevent division by zero in clk_double_div_recalc_rate()

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.