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Message-ID: <07594a59-c999-4592-84b8-4e163d3edba4@amlogic.com>
Date: Fri, 8 Nov 2024 15:59:44 +0800
From: Chuan Liu <chuan.liu@...ogic.com>
To: Jerome Brunet <jbrunet@...libre.com>, Stephen Boyd <sboyd@...nel.org>
Cc: Neil Armstrong <neil.armstrong@...aro.org>,
Kevin Hilman <khilman@...libre.com>,
Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-amlogic@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH] clk: core: refine disable unused clocks
hi Jerome:
Tranks for your REF. I looked at your patch and there are some
parts that I don't quite understand: The original intention of
CLK_OPS_PARENT_ENABLE was to solve the issue of "parents need enable
_during _gate/ungate, set rate and re-parent" when setting a clock. After setting
the clock, it can still be disabled. However, from what I see in your
patch, the handling logic seems more like "parents need _always _ gate
during clock gate period"?
On 10/4/2024 9:39 PM, Jerome Brunet wrote:
> [ EXTERNAL EMAIL ]
>
> As it as been pointed out numerous times, flagging a clock with
> CLK_IGNORE_UNUSED does _not_ guarantee that clock left enabled will stay
> on. The clock will get disabled if any enable/disable cycle happens on it
> or its parent clocks.
>
> Because enable/disable cycles will disable unused clocks,
> clk_disable_unused() should not trigger such cycle. Doing so disregard
> the flag if set for any parent clocks. This is problematic with
> CLK_OPS_PARENT_ENABLE handling.
>
> To solve this, and a couple other issues, pass the parent status to the
> child while walking the subtree, and return whether child ignored disable,
> or not.
>
> * Knowing the parent status allows to safely disable clocks with
> CLK_OPS_PARENT_ENABLE when the parent is enabled. Otherwise it means
> that, while the clock is not gated it is effectively disabled. Turning on
> the parents to sanitize the sitation would bring back our initial
> problem, so just let it sanitize itself when the clock gets used.
>
> * If a clock is not actively used (enabled_count == 0), does not have
> CLK_IGNORE_UNUSED but the hw enabled all the way to the root clock, and a
> child ignored the disable, it should ignore the disable too. Doing so
> avoids disabling what is feading the children. Let the flag trickle down
> the tree. This has the added benefit to transfer the information to the
> unprepare path, so we don't unprepare the parent of a clock that ignored
> a disable.
>
> * An enabled clock must be prepared in CCF but we can't rely solely on
> counts at clk_disable_unused() stage. Make sure an enabled clock is
> considered prepared too, even if does not implement the related callback.
> Also make sure only disabled clocks get unprepared.
>
> Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
> ---
>
> This is sent as an RFC to continue the discussion started by Chuan.
> It is not meant to be applied as it is.
>
>
> drivers/clk/clk.c | 92 ++++++++++++++++++++++++++++++-----------------
> 1 file changed, 60 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index d02451f951cf..41c4504a41f1 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -332,17 +332,6 @@ static bool clk_core_is_enabled(struct clk_core *core)
> }
> }
>
> - /*
> - * This could be called with the enable lock held, or from atomic
> - * context. If the parent isn't enabled already, we can't do
> - * anything here. We can also assume this clock isn't enabled.
> - */
> - if ((core->flags & CLK_OPS_PARENT_ENABLE) && core->parent)
This judgment of CLK_OPS_PARENT_ENABLE seems redundant. According to
normal logic, if the parent is disabled, its children will also be
forced to disable. This seems unrelated to whether CLK_OPS_PARENT_ENABLE
is configured.😳
> - if (!clk_core_is_enabled(core->parent)) {
> - ret = false;
> - goto done;
> - }
> -
> ret = core->ops->is_enabled(core->hw);
> done:
> if (core->rpm_enabled)
> @@ -1454,22 +1443,39 @@ static void clk_core_disable_unprepare(struct clk_core *core)
> clk_core_unprepare_lock(core);
> }
>
> -static void __init clk_unprepare_unused_subtree(struct clk_core *core)
> +static bool __init clk_unprepare_unused_subtree(struct clk_core *core,
> + bool parent_prepared)
> {
> struct clk_core *child;
> + bool prepared;
>
> lockdep_assert_held(&prepare_lock);
>
> + /*
> + * Relying on count is not possible at this stage, so consider
> + * prepared an enabled clock, in case only .is_enabled() is
> + * implemented
> + */
> + if (parent_prepared)
> + prepared = (clk_core_is_prepared(core) ||
> + clk_core_is_enabled(core));
> + else
> + prepared = false;
> +
> hlist_for_each_entry(child, &core->children, child_node)
> - clk_unprepare_unused_subtree(child);
> + if (clk_unprepare_unused_subtree(child, prepared) &&
> + prepared && !core->prepare_count)
> + core->flags |= CLK_IGNORE_UNUSED;
>
> - if (core->prepare_count)
> - return;
> + if (core->flags & CLK_IGNORE_UNUSED || core->prepare_count)
> + goto out;
>
> - if (core->flags & CLK_IGNORE_UNUSED)
> - return;
> + if (!parent_prepared && (core->flags & CLK_OPS_PARENT_ENABLE))
> + goto out;
>
> - if (clk_core_is_prepared(core)) {
> + /* Do not unprepare an enabled clock */
> + if (clk_core_is_prepared(core) &&
> + !clk_core_is_enabled(core)) {
> trace_clk_unprepare(core);
> if (core->ops->unprepare_unused)
> core->ops->unprepare_unused(core->hw);
> @@ -1477,27 +1483,50 @@ static void __init clk_unprepare_unused_subtree(struct clk_core *core)
> core->ops->unprepare(core->hw);
> trace_clk_unprepare_complete(core);
> }
> +
> +out:
> + return (core->flags & CLK_IGNORE_UNUSED) && prepared;
> }
>
> -static void __init clk_disable_unused_subtree(struct clk_core *core)
> +static bool __init clk_disable_unused_subtree(struct clk_core *core,
> + bool parent_enabled)
> {
> struct clk_core *child;
> unsigned long flags;
> + bool enabled;
>
> lockdep_assert_held(&prepare_lock);
>
> - hlist_for_each_entry(child, &core->children, child_node)
> - clk_disable_unused_subtree(child);
> + flags = clk_enable_lock();
>
> - if (core->flags & CLK_OPS_PARENT_ENABLE)
> - clk_core_prepare_enable(core->parent);
> + /* Check if the clock is enabled from root to this clock */
> + if (parent_enabled)
> + enabled = clk_core_is_enabled(core);
> + else
> + enabled = false;
>
> - flags = clk_enable_lock();
> + hlist_for_each_entry(child, &core->children, child_node)
> + /*
> + * If any child ignored disable, this clock should too,
> + * unless there is, valid reason for the clock to be enabled
> + */
> + if (clk_disable_unused_subtree(child, enabled) &&
> + enabled && !core->enable_count)
> + core->flags |= CLK_IGNORE_UNUSED;
>
> - if (core->enable_count)
> + if (core->flags & CLK_IGNORE_UNUSED || core->enable_count)
> goto unlock_out;
>
> - 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))
> 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
>
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