Quoting Dong Aisheng (2016-04-20 02:34:35) > On Freescale i.MX7D platform, all clocks operations, including > enable/disable, rate change and re-parent, requires its parent > clock on. Current clock core can not support it well. > This patch introduce a new flag CLK_OPS_PARENT_ON to handle this > special case in clock core that enable its parent clock firstly for > each operation and disable it later after operation complete. > > The patch part 1 fixes the possible disabling clocks while its parent > is off during kernel booting phase in clk_disable_unused_subtree(). > > Before the completion of kernel booting, clock tree is still not built > completely, there may be a case that the child clock is on but its > parent is off which could be caused by either HW initial reset state > or bootloader initialization. > > Taking bootloader as an example, we may enable all clocks in HW by default. > And during kernel booting time, the parent clock could be disabled in its > driver probe due to calling clk_prepare_enable and clk_disable_unprepare. > Because it's child clock is only enabled in HW while its SW usecount > in clock tree is still 0, so clk_disable of parent clock will gate > the parent clock in both HW and SW usecount ultimately. Then there will > be a child clock is still on in HW but its parent is already off. > > Later in clk_disable_unused(), this clock disable accessing while its > parent off will cause system hang due to the limitation of HW which > must require its parent on. > > This patch simply enables the parent clock first before disabling > if flag CLK_OPS_PARENT_ON is set in clk_disable_unused_subtree(). > This is a simple solution and only affects booting time. > > After kernel booting up the clock tree is already created, there will > be no case that child is off but its parent is off. > So no need do this checking for normal clk_disable() later. > > Cc: Michael Turquette <mturque...@baylibre.com> > Cc: Stephen Boyd <sb...@codeaurora.org> > Cc: Shawn Guo <shawn...@kernel.org> > Signed-off-by: Dong Aisheng <aisheng.d...@nxp.com> > --- > drivers/clk/clk.c | 5 +++++ > include/linux/clk-provider.h | 2 ++ > 2 files changed, 7 insertions(+) > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c > index 9f944d4..1f054d1a 100644 > --- a/drivers/clk/clk.c > +++ b/drivers/clk/clk.c > @@ -765,6 +765,9 @@ static void clk_disable_unused_subtree(struct clk_core > *core) > hlist_for_each_entry(child, &core->children, child_node) > clk_disable_unused_subtree(child); > > + if (core->flags & CLK_OPS_PARENT_ON) > + clk_core_prepare_enable(core->parent); > + > flags = clk_enable_lock(); > > if (core->enable_count) > @@ -789,6 +792,8 @@ static void clk_disable_unused_subtree(struct clk_core > *core) > > unlock_out: > clk_enable_unlock(flags); > + if (core->flags & CLK_OPS_PARENT_ON) > + clk_core_disable_unprepare(core->parent); > } > > static bool clk_ignore_unused; > diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h > index 15628644..c878f9c 100644 > --- a/include/linux/clk-provider.h > +++ b/include/linux/clk-provider.h > @@ -33,6 +33,8 @@ > #define CLK_RECALC_NEW_RATES BIT(9) /* recalc rates after notifications */ > #define CLK_SET_RATE_UNGATE BIT(10) /* clock needs to run to set rate */ > #define CLK_IS_CRITICAL BIT(11) /* do not gate, ever */ > +/* parents need on during gate/ungate, set rate and re-parent */ > +#define CLK_OPS_PARENT_ON BIT(12)
Hi Dong, In the clk framework we use "enabled" instead of "on". How about changing the flag to CLK_OPS_PARENT_ENABLE? Regards, Mike > > struct clk; > struct clk_hw; > -- > 1.9.1 >
