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

[Jerome Brunet]

On 2026-11-04 17:07:10+08:00, Jian Hu wrote:
> On 10/29/2026 5:47 PM, sashiko-bot at kernel.org wrote:
> 
> > 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 at 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.
> >
> > [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.
> 
> In this patch, the dividers which set CLK_DIVIDER_INVALID_ZERO use 
> divider_determine_rate(),
> 
> not divider_ro_determine_rate().

Yet the point raised is valid. The change must work for everyone, not just you.

-- 
Jerome