Quoting Doug Anderson (2014-11-07 17:06:58)
> With the existing code, if you find a parent for an orhpan that has
> already been prepared / enabled, you won't enable the parent. That
> can cause later problems since the clock tree isn't in a consistent
> state. Fix by propagating the prepare and enable.
>
> NOTE: this does bring up the question about whether the enable of the
> orphan actually made sense. If the orphan's parent wasn't enabled by
> default (by the bootloader or the default state of the hardware) then
> the original enable of the orphan probably didn't do what the caller
> though it would. Some users of the orphan might have preferred an
> EPROBE_DEFER be returned until we had a full path to a root clock.
> This patch doesn't address those concerns and really just syncs up the
> state.
-ECANOFWORMS
I'm thinking about this patch but I haven't quite made up my mind. It is
reasonable, but also some nice kind of error might be preferable when
preparing/enabling an orphaned clock.
Under what conditions might a clock be orphaned? An obvious example is
just bad luck during the thundering herd of clock registrations from a
driver. In this case deferring the probe might be a good idea.
However what about the case where a loadable module provides the parent
clock? It might be a long time before the orphan clocks gets picked up
from the orphanage. Is deferring probe the right thing here as well?
Regards,
Mike
>
> Tested on rk3288-evb-rk808 by temporarily considering "sclk_tsadc" as
> a critical clock (to simulate a driver enabling it at bootup).
>
> Before:
>
> clock enable_cnt prepare_cnt rate accuracy phase
> ----------------------------------------------------------------------------------------
> xin32k 0 0 32768 0 0
> sclk_hdmi_cec 0 0 32768 0 0
> sclk_otg_adp 0 0 32768 0 0
> sclk_tsadc 1 1 993 0 0
>
> After:
>
> clock enable_cnt prepare_cnt rate accuracy phase
> ----------------------------------------------------------------------------------------
> xin32k 1 1 32768 0 0
> sclk_hdmi_cec 0 0 32768 0 0
> sclk_otg_adp 0 0 32768 0 0
> sclk_tsadc 1 1 993 0 0
>
> Note that xin32k on rk808 is a clock that cannot be disabled in
> hardware (it's an always on clock), so really all we needed to do was
> to sync up the state.
>
> Signed-off-by: Doug Anderson <dianders at chromium.org>
> ---
> Changes in v2:
> - Only do the work for orphans, not for other users of __clk_reparent().
>
> drivers/clk/clk.c | 20 ++++++++++++++++++--
> 1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 4896ae9..0f04b7c 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -1652,6 +1652,22 @@ void __clk_reparent(struct clk *clk, struct clk *new_parent)
> __clk_recalc_rates(clk, POST_RATE_CHANGE);
> }
>
> +static void __clk_reparent_orphan(struct clk *clk, struct clk *new_parent)
> +{
> + __clk_reparent(clk, new_parent);
> +
> + if (clk->prepare_count) {
> + unsigned long flags;
> +
> + __clk_prepare(new_parent);
> +
> + flags = clk_enable_lock();
> + if (clk->enable_count)
> + __clk_enable(new_parent);
> + clk_enable_unlock(flags);
> + }
> +}
> +
> /**
> * clk_set_parent - switch the parent of a mux clk
> * @clk: the mux clk whose input we are switching
> @@ -1953,13 +1969,13 @@ int __clk_init(struct device *dev, struct clk *clk)
> if (orphan->num_parents && orphan->ops->get_parent) {
> i = orphan->ops->get_parent(orphan->hw);
> if (!strcmp(clk->name, orphan->parent_names[i]))
> - __clk_reparent(orphan, clk);
> + __clk_reparent_orphan(orphan, clk);
> continue;
> }
>
> for (i = 0; i < orphan->num_parents; i++)
> if (!strcmp(clk->name, orphan->parent_names[i])) {
> - __clk_reparent(orphan, clk);
> + __clk_reparent_orphan(orphan, clk);
> break;
> }
> }
> --
> 2.1.0.rc2.206.gedb03e5
>
