From a4b3518d146f150d633f7dc815bb8ee2fbc162e9 Mon Sep 17 00:00:00 2001 From: Dong Aisheng Date: Thu, 30 Jun 2016 17:31:13 +0800 Subject: clk: core: support clocks which requires parents enable (part 1) On Freescale i.MX7D platform, all clocks operations, including enable/disable, rate change and re-parent, requires its parent clock enable. Current clock core can not support it well. This patch introduce a new flag CLK_OPS_PARENT_ENABLE 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_ENABLE 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 Cc: Stephen Boyd Cc: Shawn Guo Signed-off-by: Dong Aisheng Signed-off-by: Stephen Boyd --- 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 e2e8f0c..e3bd28c 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_ENABLE) + 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_ENABLE) + 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 eeb2e69..a39c0c5 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 enable during gate/ungate, set rate and re-parent */ +#define CLK_OPS_PARENT_ENABLE BIT(12) struct clk; struct clk_hw; -- cgit v1.1