Re: [PATCH RFC RFT v2 2/3] clk: divider: add CLK_DIVIDER_INVALID_ZERO flag

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] clk: divider: unhandled zero divisor in divider_ro_determine_rate()
--

commit 5ec3118aee2f03855552c58a4a8533e035b565bc
Author: Jian Hu <jian.hu@amlogic.com>

clk: divider: add CLK_DIVIDER_INVALID_ZERO flag

This commit introduces the CLK_DIVIDER_INVALID_ZERO flag for dividers where
a zero divisor value represents an invalid hardware state rather than a
pass-through. When this flag is set and the divisor evaluates to zero,
divider_recalc_rate() returns 0 without emitting a warning.

> diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
> index f68216c65d3df..6c1523d22477c 100644
> --- a/drivers/clk/clk-divider.c
> +++ b/drivers/clk/clk-divider.c
> @@ -143,6 +143,9 @@ unsigned long divider_recalc_rate(struct clk_hw *hw, unsigned long parent_rate,
>  
>  	div = _get_div(table, val, flags, width);
>  	if (!div) {
> +		if (flags & CLK_DIVIDER_INVALID_ZERO)
> +			return 0;

[Severity: High]
Should divider_ro_determine_rate() in drivers/clk/clk-divider.c also handle
a zero divisor when CLK_DIVIDER_INVALID_ZERO or CLK_DIVIDER_ALLOW_ZERO is
set?

When a read-only divider has a register value val that maps to div == 0 via
_get_div() (for example, when CLK_DIVIDER_INVALID_ZERO is combined with
CLK_DIVIDER_ONE_BASED or an unmapped table entry alongside
CLK_DIVIDER_READ_ONLY), calling clk_round_rate() or clk_set_rate() invokes
clk_divider_determine_rate()->divider_ro_determine_rate():

drivers/clk/clk-divider.c:divider_ro_determine_rate() {
	int div;

	div = _get_div(table, val, flags, width);

	/* Even a read-only clock can propagate a rate change */
	if (clk_hw_get_flags(hw) & CLK_SET_RATE_PARENT) {
		if (!req->best_parent_hw)
			return -EINVAL;

		req->best_parent_rate = clk_hw_round_rate(req->best_parent_hw,
							  req->rate * div);
	}

	req->rate = DIV_ROUND_UP_ULL((u64)req->best_parent_rate, div);

	return 0;
}

Unlike divider_recalc_rate(), divider_ro_determine_rate() does not check for
!div before calling DIV_ROUND_UP_ULL(), which will trigger a division by zero
in the kernel when div is 0.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261029-meson_refactor_n-v2-0-ff4ac74e527b@amlogic.com?part=2

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