Re: [PATCH] clk: emit warning if fail to get parent clk

[Jun Nie <jun.nie@linaro.org>]

Stephen Boyd <sboyd@kernel.org> 于2020年10月8日周四 上午7:53写道：
>
> Quoting Jun Nie (2020-09-28 01:47:44)
> > Emit warning if fail to get parent clk to expose potential issue earlier.
> > For example, clk_hw_get_rate() will return 0 for a clock without parent core
> > while parent number is not zero. This cause opp always think it is switching
> > frequency from 0 to some other frequency. Crash may happen if we switch
> > from high frequency to low frequency and lower CPU voltage before clk rate
> > switching.
>
> Thanks for the background reasoning. It's good to know what the problem
> is. Is there any way to change OPP so it can handle this scenario
> better?

Maybe we can save latest CPU voltage and lower the voltage per opp voltage
requirement instead of clk rate requirement.
>
> >
> > Signed-off-by: Jun Nie <jun.nie@linaro.org>
> > ---
> >  drivers/clk/clk.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > index 1a27e99ccb17..78b21b888e56 100644
> > --- a/drivers/clk/clk.c
> > +++ b/drivers/clk/clk.c
> > @@ -424,6 +424,7 @@ static void clk_core_fill_parent_index(struct clk_core *core, u8 index)
> >  {
> >         struct clk_parent_map *entry = &core->parents[index];
> >         struct clk_core *parent = ERR_PTR(-ENOENT);
> > +       int emit_warn = 0;
> >
> >         if (entry->hw) {
> >                 parent = entry->hw->core;
> > @@ -443,6 +444,12 @@ static void clk_core_fill_parent_index(struct clk_core *core, u8 index)
> >         /* Only cache it if it's not an error */
> >         if (!IS_ERR(parent))
> >                 entry->core = parent;
> > +       else if (parent != ERR_PTR(-EPROBE_DEFER))
> > +               emit_warn = 1;
> > +
> > +       if (emit_warn || (!parent && core->num_parents))
> > +               pr_warn("Fail to get indexed %d parent for clk %s.",
> > +                       index, core->name);
>
> How do we know that this error isn't because the parent hasn't been
> probed yet?

Yes, this is chance that failure to probe parent also cause the error.
But I had thought there may
be unnecessary error message before the successful probing, though I
did not see it. If you think
it does not a matter, next version can emit warning on all error.

Jun