CLK_IGNORE_UNUSE looks buggy

[Barry Song]

hi Stephen, Michael,

currently we can set a CLK_IGNORE_UNUSE flag to  a clock to stop
clk_disable_unused()  from disabling it at the boot stage:

static void clk_disable_unused_subtree(struct clk_core *core)
{
...
if (core->flags & CLK_IGNORE_UNUSED)
goto unlock_out;

...
}

static int clk_disable_unused(void)
{
...
clk_unprepare_unused_subtree(core);
...

return 0;
}
late_initcall_sync(clk_disable_unused);

so if there are two clocks A and B, A is the parent of B, and A is
marked as CLK_IGNORE_UNUSED.

in boot stage if there is nobody using A and B, Linux will disable B
due to clk_disable_unused() , but keep A being enabled since A has
CLK_IGNORE_UNUSED.

but in Linux runtime, we might frequently disable /enable B in runtime
power management, this will cause A disabled since Linux will not
check CLK_IGNORE_UNUSED for runtime disabling clk .

so this makes CLK_IGNORE_UNUSE only work if we don't disable its
sub-clock at runtime. this looks making no sense.

i am thinking whether we should do some changes to make it have side
affect for runtime clk disable. otherwise, why do we want to stop it
from being disabled during boot stage?

I am not sure whether i missed something in clk core level support.

-barry