Re: [RFC PATCH] clk: core: refine disable unused clocks

[Chuan Liu]

On 11/8/2024 5:59 PM, Jerome Brunet wrote:
> [ EXTERNAL EMAIL ]
>
> On Fri 08 Nov 2024 at 17:23, Chuan Liu <chuan.liu@xxxxxxxxxxx> wrote:
>
> > > > > -       if (core->flags & CLK_IGNORE_UNUSED)
> > > > > +       /*
> > > > > +        * If the parent is disabled but the gate is open, we should sanitize
> > > > > +        * the situation. This will avoid an unexpected enable of the clock as
> > > > > +        * soon as the parent is enabled, without control of CCF.
> > > > > +        *
> > > > > +        * Doing so is not possible with a CLK_OPS_PARENT_ENABLE clock without
> > > > > +        * forcefully enabling a whole part of the subtree.  Just let the
> > > > > +        * situation resolve it self on the first enable of the clock
> > > > > +        */
> > > > > +       if (!parent_enabled && (core->flags & CLK_OPS_PARENT_ENABLE))
> > At first, I couldn't grasp the logic behind the 'return' here. Now it's
> > clear. This approach is equivalent to completely giving up on
> > handling clocks with CLK_OPS_PARENT_ENABLE feature in
> > clk_disable_unused_subtree().
> No. It's handled correctly as long as the tree is in coherent state.
>
> What is not done anymore is fixing up an inconsistent tree, by this I
> mean: A clock with CLK_OPS_PARENT_ENABLE, which report enabled from its
> own registers but has its parent disabled.
>
> In that particular case, clk_disable_unused_subtree() won't be turning on
> everything to properly disable that one clock. That is the root cause of
> the problem you reported initially. The clock is disabled anyway.
>
> Every other case are properly handled (at least I think).

name              en_sts            flags
clk_a                1          CLK_IGNORE_UNUSED
    clk_b            0                0
        clk_c        1         CLK_OPS_PARENT_ENABLE

Based on the above case:
1. When 'clk_c' is configured with CLK_OPS_PARENT_ENABLE, disabling
'clk_c' requires enabling 'clk_b' first (disabling 'clk_c' before
disabling 'clk_b'). How can to ensure that during the period of
disabling 'clk_c', 'clk_b' remains enabled?

2. 'clk_c' is not configured with CLK_IGNORE_UNUSED, it should be
disabled later. However, here it goes to a 'goto' statement and then
return 'false', ultimately resulting in 'clk_c' not being disabled?

> > > > >                    goto unlock_out;
> > > > >
> > > > >            /*
> > > > > @@ -1516,8 +1545,7 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
> > > > >
> > > > >     unlock_out:
> > > > >            clk_enable_unlock(flags);
> > > > > -       if (core->flags & CLK_OPS_PARENT_ENABLE)
> > > > > -               clk_core_disable_unprepare(core->parent);
> > > > > +       return (core->flags & CLK_IGNORE_UNUSED) && enabled;
> > > > >     }
> > > > >
> > > > >     static bool clk_ignore_unused __initdata;
> > > > > @@ -1550,16 +1578,16 @@ static int __init clk_disable_unused(void)
> > > > >            clk_prepare_lock();
> > > > >
> > > > >            hlist_for_each_entry(core, &clk_root_list, child_node)
> > > > > -               clk_disable_unused_subtree(core);
> > > > > +               clk_disable_unused_subtree(core, true);
> > > > >
> > > > >            hlist_for_each_entry(core, &clk_orphan_list, child_node)
> > > > > -               clk_disable_unused_subtree(core);
> > > > > +               clk_disable_unused_subtree(core, true);
> > > > >
> > > > >            hlist_for_each_entry(core, &clk_root_list, child_node)
> > > > > -               clk_unprepare_unused_subtree(core);
> > > > > +               clk_unprepare_unused_subtree(core, true);
> > > > >
> > > > >            hlist_for_each_entry(core, &clk_orphan_list, child_node)
> > > > > -               clk_unprepare_unused_subtree(core);
> > > > > +               clk_unprepare_unused_subtree(core, true);
> > > > >
> > > > >            clk_prepare_unlock();
> > > > >
> > > > > --
> > > > > 2.45.2
> > > --
> > > Jerome
> --
> Jerome