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Message-ID: <1jed51tjhj.fsf@starbuckisacylon.baylibre.com>
Date: Mon, 30 Sep 2024 14:27:04 +0200
From: Jerome Brunet <jbrunet@...libre.com>
To: Chuan Liu via B4 Relay <devnull+chuan.liu.amlogic.com@...nel.org>
Cc: Michael Turquette <mturquette@...libre.com>, Stephen Boyd
<sboyd@...nel.org>, Neil Armstrong <neil.armstrong@...aro.org>, Kevin
Hilman <khilman@...libre.com>, Martin Blumenstingl
<martin.blumenstingl@...glemail.com>, chuan.liu@...ogic.com,
linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-amlogic@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] clk: Fix the CLK_IGNORE_UNUSED failure issue
On Sun 29 Sep 2024 at 14:10, Chuan Liu via B4 Relay <devnull+chuan.liu.amlogic.com@...nel.org> wrote:
> From: Chuan Liu <chuan.liu@...ogic.com>
>
> When the clk_disable_unused_subtree() function disables an unused clock,
> if CLK_OPS_PARENT_ENABLE is configured on the clock,
> clk_core_prepare_enable() and clk_core_disable_unprepare() are called
> directly, and these two functions do not determine CLK_IGNORE_UNUSED,
> This causes the clock to be disabled even if CLK_IGNORE_UNUSED is
> configured when clk_core_disable_unprepare() is called.
>
> Two new functions clk_disable_unprepare_unused() and
> clk_prepare_enable_unused() are added to resolve the preceding
> situation. The CLK_IGNORE_UNUSED judgment logic is added to these two
> functions. To prevent clock configuration CLK_IGNORE_UNUSED from
> possible failure.
>
> Change-Id: I56943e17b86436254f07d9b8cdbc35599328d519
> Signed-off-by: Chuan Liu <chuan.liu@...ogic.com>
> ---
> drivers/clk/clk.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 65 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 285ed1ad8a37..5d3316699b57 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -94,6 +94,7 @@ struct clk_core {
> struct hlist_node debug_node;
> #endif
> struct kref ref;
> + bool ignore_enabled;
> };
>
> #define CREATE_TRACE_POINTS
> @@ -1479,6 +1480,68 @@ static void __init clk_unprepare_unused_subtree(struct clk_core *core)
> }
> }
>
> +static void __init clk_disable_unprepare_unused(struct clk_core *core)
> +{
> + unsigned long flags;
> +
> + lockdep_assert_held(&prepare_lock);
> +
> + if (!core)
> + return;
> +
> + if ((core->enable_count == 0) && core->ops->disable &&
> + !core->ignore_enabled) {
> + flags = clk_enable_lock();
Used core->enable_count without taking the lock
> + core->ops->disable(core->hw);
If the there is any CLK_IS_CRITICAL in the path, it is game over.
You've basically disregarded all the other CCF flags which are equally
important to the ones you are dealing with.
> + clk_enable_unlock(flags);
> + }
> +
> + if ((core->prepare_count == 0) && core->ops->unprepare &&
> + !core->ignore_enabled)
> + core->ops->unprepare(core->hw);
> +
> + core->ignore_enabled = false;
> +
> + clk_disable_unprepare_unused(core->parent);
Here you are disabling the parent of any CLK_IGNORE_UNUSED clock.
IMO, the problem is not solved. It just shifted.
> +}
> +
> +static int __init clk_prepare_enable_unused(struct clk_core *core)
> +{
> + int ret = 0;
> + unsigned long flags;
> +
> + lockdep_assert_held(&prepare_lock);
> +
> + if (!core)
> + return 0;
> +
> + ret = clk_prepare_enable_unused(core->parent);
> + if (ret)
> + return ret;
That's adding another recursion in CCF, something Stephen would like to remove
> +
> + if ((core->flags & CLK_IGNORE_UNUSED) && clk_core_is_enabled(core))
> + core->ignore_enabled = true;
> +
> + if ((core->prepare_count == 0) && core->ops->prepare) {
> + ret = core->ops->prepare(core->hw);
> + if (ret)
> + goto disable_unprepare;
> + }
> +
> + if ((core->enable_count == 0) && core->ops->enable) {
> + flags = clk_enable_lock();
> + ret = core->ops->enable(core->hw);
> + clk_enable_unlock(flags);
> + if (ret)
> + goto disable_unprepare;
> + }
> +
> + return 0;
> +disable_unprepare:
> + clk_disable_unprepare_unused(core->parent);
> + return ret;
> +}
> +
> static void __init clk_disable_unused_subtree(struct clk_core *core)
> {
> struct clk_core *child;
> @@ -1490,7 +1553,7 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
> clk_disable_unused_subtree(child);
>
> if (core->flags & CLK_OPS_PARENT_ENABLE)
> - clk_core_prepare_enable(core->parent);
> + clk_prepare_enable_unused(core->parent);
>
> flags = clk_enable_lock();
>
> @@ -1517,7 +1580,7 @@ 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);
> + clk_disable_unprepare_unused(core->parent);
> }
>
> static bool clk_ignore_unused __initdata;
--
Jerome
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