[PATCH] clk: disable unused clocks registered after boot

[PATCH] clk: disable unused clocks registered after boot

[alexandre.belloni]

From: Alexandre Belloni <alexandre.belloni@bootlin.com>

clk_disable_unused() only runs once as a late_initcall, so clocks
registered afterwards by loading a module are never checked and may be left
running needlessly.

So record when clk_disable_unused has run and afterwards, schedule a
delayed work to run the scan when new clocks are registered.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
---
 drivers/clk/clk.c | 50 +++++++++++++++++++++++++++++++++++------------
 1 file changed, 37 insertions(+), 13 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index fef87167a60b..f455d2482a5a 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -24,6 +24,7 @@
 #include <linux/spinlock.h>
 #include <linux/string.h>
 #include <linux/stringhash.h>
+#include <linux/workqueue.h>
 
 #include "clk.h"
 
@@ -47,6 +48,10 @@ static LIST_HEAD(clk_notifier_list);
 static HLIST_HEAD(clk_rpm_list);
 static DEFINE_MUTEX(clk_rpm_list_lock);
 
+static bool clk_disable_unused_done;
+
+#define CLK_DISABLE_UNUSED_DELAY	(HZ / 2)
+
 static const struct hlist_head *all_lists[] = {
 	&clk_root_list,
 	&clk_orphan_list,
@@ -1511,7 +1516,7 @@ 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 void clk_unprepare_unused_subtree(struct clk_core *core)
 {
 	struct clk_core *child;
 
@@ -1536,7 +1541,7 @@ static void __init clk_unprepare_unused_subtree(struct clk_core *core)
 	}
 }
 
-static void __init clk_disable_unused_subtree(struct clk_core *core)
+static void clk_disable_unused_subtree(struct clk_core *core)
 {
 	struct clk_core *child;
 	unsigned long flags;
@@ -1585,21 +1590,14 @@ static int __init clk_ignore_unused_setup(char *__unused)
 }
 __setup("clk_ignore_unused", clk_ignore_unused_setup);
 
-static int __init clk_disable_unused(void)
+static void clk_disable_unused(void)
 {
 	struct clk_core *core;
 	int ret;
 
-	if (clk_ignore_unused) {
-		pr_warn("clk: Not disabling unused clocks\n");
-		return 0;
-	}
-
-	pr_info("clk: Disabling unused clocks\n");
-
 	ret = clk_pm_runtime_get_all();
 	if (ret)
-		return ret;
+		return;
 	/*
 	 * Grab the prepare lock to keep the clk topology stable while iterating
 	 * over clks.
@@ -1621,10 +1619,31 @@ static int __init clk_disable_unused(void)
 	clk_prepare_unlock();
 
 	clk_pm_runtime_put_all();
+}
+
+static void clk_disable_unused_workfn(struct work_struct *work)
+{
+	clk_disable_unused();
+}
+
+static DECLARE_DELAYED_WORK(clk_disable_unused_work, clk_disable_unused_workfn);
+
+static int __init clk_disable_unused_init(void)
+{
+	if (clk_ignore_unused) {
+		pr_warn("clk: Not disabling unused clocks\n");
+		return 0;
+	}
+
+	pr_info("clk: Disabling unused clocks\n");
+
+	clk_disable_unused();
+
+	WRITE_ONCE(clk_disable_unused_done, true);
 
 	return 0;
 }
-late_initcall_sync(clk_disable_unused);
+late_initcall_sync(clk_disable_unused_init);
 
 static int clk_core_determine_round_nolock(struct clk_core *core,
 					   struct clk_rate_request *req)
@@ -4462,8 +4481,13 @@ __clk_register(struct device *dev, struct device_node *np, struct clk_hw *hw)
 	clk_core_link_consumer(core, hw->clk);
 
 	ret = __clk_core_init(core);
-	if (!ret)
+	if (!ret) {
+		if (READ_ONCE(clk_disable_unused_done))
+			mod_delayed_work(system_power_efficient_wq,
+					 &clk_disable_unused_work,
+					 CLK_DISABLE_UNUSED_DELAY);
 		return hw->clk;
+	}
 
 	clk_prepare_lock();
 	clk_core_unlink_consumer(hw->clk);
-- 
2.55.0

Re: [PATCH] clk: disable unused clocks registered after boot

[Brian Masney]

Hi Alexandre,

On Thu, Sep 17, 2026 at 04:40:10PM +0200, alexandre.belloni@bootlin.com wrote:
> From: Alexandre Belloni <alexandre.belloni@bootlin.com>
> 
> clk_disable_unused() only runs once as a late_initcall, so clocks
> registered afterwards by loading a module are never checked and may be left
> running needlessly.
> 
> So record when clk_disable_unused has run and afterwards, schedule a
> delayed work to run the scan when new clocks are registered.
> 
> Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

We're actually in the process of redoing the way clk_disable_unused is
handled. I posted a series to add sync_state support to the clk
framework:

https://lore.kernel.org/linux-clk/20260626-clk-sync-state-v1-0-4156d8196dc8@redhat.com/

Will you be at Linux Plumbers in Prague in 2.5 weeks? If so, come to
this talk where we will talk about the clk subsystem.

    Evolving support for sync_state to subsystems beyond genpd 
    https://lpc.events/event/20/contributions/2504/

Brian

Re: [PATCH] clk: disable unused clocks registered after boot

[Alexandre Belloni]

Hello,

On 17/09/2026 12:01:42-0400, Brian Masney wrote:
> Hi Alexandre,
> 
> On Thu, Sep 17, 2026 at 04:40:10PM +0200, alexandre.belloni@bootlin.com wrote:
> > From: Alexandre Belloni <alexandre.belloni@bootlin.com>
> > 
> > clk_disable_unused() only runs once as a late_initcall, so clocks
> > registered afterwards by loading a module are never checked and may be left
> > running needlessly.
> > 
> > So record when clk_disable_unused has run and afterwards, schedule a
> > delayed work to run the scan when new clocks are registered.
> > 
> > Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
> 
> We're actually in the process of redoing the way clk_disable_unused is
> handled. I posted a series to add sync_state support to the clk
> framework:
> 
> https://lore.kernel.org/linux-clk/20260626-clk-sync-state-v1-0-4156d8196dc8@redhat.com/
> 
> Will you be at Linux Plumbers in Prague in 2.5 weeks? If so, come to
> this talk where we will talk about the clk subsystem.
> 
>     Evolving support for sync_state to subsystems beyond genpd 
>     https://lpc.events/event/20/contributions/2504/
> 

I will be at plumbers and I'll try to attend, thanks!

For reference, this is the reason for the patch:
https://lore.kernel.org/all/2ce03d3b4cd9cce8e32fe1fe1ffbea5760bf9ef3.camel@siemens.com/

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

Re: [PATCH] clk: disable unused clocks registered after boot

[Brian Masney]

Hi Alexandre,

On Thu, Sep 17, 2026 at 07:23:36PM +0200, Alexandre Belloni wrote:
> On 17/09/2026 12:01:42-0400, Brian Masney wrote:
> > On Thu, Sep 17, 2026 at 04:40:10PM +0200, alexandre.belloni@bootlin.com wrote:
> > > From: Alexandre Belloni <alexandre.belloni@bootlin.com>
> > > 
> > > clk_disable_unused() only runs once as a late_initcall, so clocks
> > > registered afterwards by loading a module are never checked and may be left
> > > running needlessly.
> > > 
> > > So record when clk_disable_unused has run and afterwards, schedule a
> > > delayed work to run the scan when new clocks are registered.
> > > 
> > > Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
> > 
> > We're actually in the process of redoing the way clk_disable_unused is
> > handled. I posted a series to add sync_state support to the clk
> > framework:
> > 
> > https://lore.kernel.org/linux-clk/20260626-clk-sync-state-v1-0-4156d8196dc8@redhat.com/
> > 
> > Will you be at Linux Plumbers in Prague in 2.5 weeks? If so, come to
> > this talk where we will talk about the clk subsystem.
> > 
> >     Evolving support for sync_state to subsystems beyond genpd 
> >     https://lpc.events/event/20/contributions/2504/
> > 
> 
> I will be at plumbers and I'll try to attend, thanks!
> 
> For reference, this is the reason for the patch:
> https://lore.kernel.org/all/2ce03d3b4cd9cce8e32fe1fe1ffbea5760bf9ef3.camel@siemens.com/

Can you try running with my sync_state patch set before LPC and see if
it works as expected for you? Be sure to leave clk_ignore_unused off the
kernel command line.

https://lore.kernel.org/linux-clk/20260626-clk-sync-state-v1-0-4156d8196dc8@redhat.com/

Brian