Re: [PATCH 5/5] clk: implement sync_state support

[Krzysztof Kozlowski]

On 30/06/2026 10:57, Xuyang Dong wrote:
>>>>
>>>> The existing support for disabling unused clks runs in the late initcall
>>>> stage, and it has been known for a long time that this is broken since
>>>> it runs too early in the boot up process. It doesn't work for kernel
>>>> modules, and it also doesn't work if all of the consumers haven't fully
>>>> probed yet. Folks have long recommended to boot certain platforms with
>>>> clk_ignore_unused to work around issues with disabling unused clks.
>>>>
>>>>
>>>> Let's go ahead and add a framework-level sync_state callback for the clk
>>>> subsystem. If a driver doesn't have a sync_state callback configured,
>>>> which is the 99+% use case today, then let's set it up to use the
>>>> clk_sync_state() introduced in this commit so that no driver changes
>>>> are needed.
>>>>
>>>>
>>>> At the time of this writing, there are currently only 7 clk drivers that
>>>> implement sync_state, and all are Qualcomm SoCs where they interact with
>>>> the interconnect framework via icc_sync_state(). A shared helper has
>>>> been created for this platform that calls clk_sync_state(). It is
>>>> expected that any new clk drivers that want to implement their own
>>>> sync_state will also need to call clk_sync_state() at the end of their
>>>> custom sync_state callback.
>>>>
>>>>
>>>> There will be several stages of disabling unused clks:
>>>>
>>>>
>>>> - The first phase will be executed at late_initcall and it will only
>>>>   disable unused clks that do not have a struct dev.
>>>> - The sync_state callback will be invoked for each clk driver once all
>>>>   consumers have probed.
>>>>
>>>>
>>>> This is based on previous attempts by Saravana Kannan and Abel Vesa
>>>> that are linked below.
>>>>
>>>>
>>>> This change was tested on a Thinkpad x13s laptop.
>>>>
>>>>
>>>>     [    0.308051] clk: Disabling unused clocks not associated with a device
>>>>     [    6.541069] qcom_aoss_qmp c300000.power-management: clk: Disabling unused clocks
>>>>     [    6.843310] qcom-qmp-pcie-phy 1c24000.phy: clk: Disabling unused clocks
>>>>     [    7.604556] qcom-qmp-pcie-phy 1c14000.phy: clk: Disabling unused clocks
>>>>     [    8.446161] qcom-qmp-usb-phy 88f1000.phy: clk: Disabling unused clocks
>>>>     [    8.446293] qcom-qmp-usb-phy 88ef000.phy: clk: Disabling unused clocks
>>>>     [    8.546067] qcom-qmp-combo-phy 88eb000.phy: clk: Disabling unused clocks
>>>>     [    8.546203] qcom-qmp-combo-phy 8903000.phy: clk: Disabling unused clocks
>>>>     [    8.546254] qcom-edp-phy aec5a00.phy: clk: Disabling unused clocks
>>>>     [   15.436834] qcom-cpufreq-hw 18591000.cpufreq: clk: Disabling unused clocks
>>>>     [   15.436953] clk-rpmh 18200000.rsc:clock-controller: clk: Disabling unused clocks
>>>>     [   15.723348] qcom-qmp-pcie-phy 1c06000.phy: clk: Disabling unused clocks
>>>>     [   21.063241] q6prm-lpass-clock 3000000.remoteproc:glink-edge:gpr:service@2:clock-controller: clk: Disabling unused clocks
>>>>     [   21.081996] va_macro 3370000.codec: clk: Disabling unused clocks
>>>>     [   21.092740] rx_macro 3200000.rxmacro: clk: Disabling unused clocks
>>>>     [   21.118261] wsa_macro 3240000.codec: clk: Disabling unused clocks
>>>>     [   21.128758] tx_macro 3220000.txmacro: clk: Disabling unused clocks
>>>>
>>>>
>>>> Tested-by: Jens Glathe <jens.glathe@xxxxxxxxxxxxxxxxxxxxxx>
>>>> Signed-off-by: Brian Masney <bmasney@xxxxxxxxxx>
>>>> Link: https://www.youtube.com/watch?v=tXYzM8yLIQA
>>>> Link: https://lore.kernel.org/all/20210407034456.516204-1-saravanak@xxxxxxxxxx/
>>>> Link: https://lore.kernel.org/all/20221227204528.1899863-1-abel.vesa@xxxxxxxxxx/
>>>> ---
>>>>  drivers/clk/clk.c | 72 ++++++++++++++++++++++++++++++++++++++---------
>>>>  1 file changed, 59 insertions(+), 13 deletions(-)
>>>>
>>>>
>>>> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
>>>> index 9cb2b42d1be4..7a15cceec620 100644
>>>> --- a/drivers/clk/clk.c
>>>> +++ b/drivers/clk/clk.c
>>>> @@ -1442,14 +1442,39 @@ 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)
>>>> +/*
>>>> + * Returns true if @core should be skipped during an unused-clock sweep for
>>>> + * @dev.  When @dev is NULL the sweep is the global late_initcall pass; when
>>>> + * @dev is non-NULL the sweep is a per-device sync_state pass.
>>>> + */
>>>> +static bool clk_core_skip_unused(struct clk_core *core, struct device *dev)
>>>> +{
>>>> +	/*
>>>> +	 * At late_initcall, skip clocks that belong to a device — they will be
>>>> +	 * handled at sync_state time.
>>>> +	 */
>>>> +	if (!dev && core->dev)
>>>> +		return true;
>>>> +
>>>> +	/* When called from sync_state, only process clocks for this device. */
>>>> +	if (dev && core->dev != dev)
>>>> +		return true;
>>>> +
>>>> +	return false;
>>>> +}
>>>> +
>>>> +static void clk_unprepare_unused_subtree(struct clk_core *core,
>>>> +					 struct device *dev)
>>>>  {
>>>>  	struct clk_core *child;
>>>>  
>>>>  	lockdep_assert_held(&prepare_lock);
>>>>  
>>>>  	hlist_for_each_entry(child, &core->children, child_node)
>>>> -		clk_unprepare_unused_subtree(child);
>>>> +		clk_unprepare_unused_subtree(child, dev);
>>>> +
>>>> +	if (clk_core_skip_unused(core, dev))
>>>> +		return;
>>>>  
>>>>  	if (core->prepare_count)
>>>>  		return;
>>>> @@ -1467,7 +1492,8 @@ 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 device *dev)
>>>>  {
>>>>  	struct clk_core *child;
>>>>  	unsigned long flags;
>>>> @@ -1475,7 +1501,10 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
>>>>  	lockdep_assert_held(&prepare_lock);
>>>>  
>>>>  	hlist_for_each_entry(child, &core->children, child_node)
>>>> -		clk_disable_unused_subtree(child);
>>>> +		clk_disable_unused_subtree(child, dev);
>>>> +
>>>> +	if (clk_core_skip_unused(core, dev))
>>>> +		return;
>>>>  
>>>>  	if (core->flags & CLK_OPS_PARENT_ENABLE)
>>>>  		clk_core_prepare_enable(core->parent);
>>>> @@ -1508,7 +1537,7 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
>>>>  		clk_core_disable_unprepare(core->parent);
>>>>  }
>>>>  
>>>> -static bool clk_ignore_unused __initdata;
>>>> +static bool clk_ignore_unused;
>>>>  static int __init clk_ignore_unused_setup(char *__unused)
>>>>  {
>>>>  	clk_ignore_unused = true;
>>>> @@ -1516,7 +1545,7 @@ 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 int __clk_disable_unused(struct device *dev)
>>>>  {
>>>>  	struct clk_core *core;
>>>>  	int ret;
>>>> @@ -1526,7 +1555,10 @@ static int __init clk_disable_unused(void)
>>>>  		return 0;
>>>>  	}
>>>>  
>>>> -	pr_info("clk: Disabling unused clocks\n");
>>>> +	if (dev)
>>>> +		dev_info(dev, "clk: Disabling unused clocks\n");
>>>> +	else
>>>> +		pr_info("clk: Disabling unused clocks not associated with a device\n");
>>>>  
>>>>  	ret = clk_pm_runtime_get_all();
>>>>  	if (ret)
>>>> @@ -1538,16 +1570,16 @@ 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, dev);
>>>>  
>>>>  	hlist_for_each_entry(core, &clk_orphan_list, child_node)
>>>> -		clk_disable_unused_subtree(core);
>>>> +		clk_disable_unused_subtree(core, dev);
>>>>  
>>>>  	hlist_for_each_entry(core, &clk_root_list, child_node)
>>>> -		clk_unprepare_unused_subtree(core);
>>>> +		clk_unprepare_unused_subtree(core, dev);
>>>>  
>>>>  	hlist_for_each_entry(core, &clk_orphan_list, child_node)
>>>> -		clk_unprepare_unused_subtree(core);
>>>> +		clk_unprepare_unused_subtree(core, dev);
>>>>  
>>>>  	clk_prepare_unlock();
>>>>  
>>>> @@ -1555,11 +1587,16 @@ static int __init clk_disable_unused(void)
>>>>  
>>>>  	return 0;
>>>>  }
>>>> +
>>>> +static int __init clk_disable_unused(void)
>>>> +{
>>>> +	return __clk_disable_unused(NULL);
>>>> +}
>>>>  late_initcall_sync(clk_disable_unused);
>>>>  
>>>>  void clk_sync_state(struct device *dev)
>>>>  {
>>>> -	/* Will fill in */
>>>> +	__clk_disable_unused(dev);
>>>>  }
>>>>  EXPORT_SYMBOL_GPL(clk_sync_state);
>>>>  
>>>> @@ -4345,8 +4382,17 @@ __clk_register(struct device *dev, struct device_node *np, struct clk_hw *hw)
>>>>  	core->dev = dev;
>>>>  	clk_pm_runtime_init(core);
>>>>  	core->of_node = np;
>>>> -	if (dev && dev->driver)
>>>> +	if (dev && dev->driver) {
>>>>  		core->owner = dev->driver->owner;
>>>> +
>>>> +		/*
>>>> +		 * If a clk provider sets their own sync_state, then it needs to
>>>> +		 * also call clk_sync_state(). dev_set_drv_sync_state() won't
>>>> +		 * overwrite the sync_state callback, and this call will fail
>>>> +		 * with -EBUSY.
>>>> +		 */
>>>> +		dev_set_drv_sync_state(dev, clk_sync_state);
>>>> +	}
>>>>  	core->hw = hw;
>>>>  	core->flags = init->flags;
>>>>  	core->num_parents = init->num_parents;
>>>
>>> Hi Brian,
>>>
>>> Thank you for the patch set. I tested this in my tree on Sifive HiFive 
>>> Premier P550, and it behaved correctly.
>>>
>>> Tested-by: Xuyang Dong <dongxuyang@xxxxxxxxxxxxxxxxxx> # hfp550
>>
>> If I understand correctly your platform, you tested nothing. You
>> executed no code from common part and no code from the drivers listed
>> here. This is not a real test in such case.
>>
>> When you test code, please actually be sure you execute the tested code.
>>
>> I am afraid the tag is not applicable.
>>
> 
> Hi Krzysztof and Brian,
> 
> I applied this series via b4 shazam 
> https://lore.kernel.org/all/20260616-clk-sync-state-v2-0-15f82c64d95c@xxxxxxxxxx/.
> 
> I dropped 'clk_ignore_unused' at compile time. After booting the system, 
> I ran dmesg | grep "unused clock" and observed the following output:
> 
> [root@eswin-os:~]$ dmesg | grep "unused clock"
> [    6.388986] clk: Disabling unused clocks not associated with a device
> [    6.395585] eic7700-clock 51828000.clock-controller: clk: Disabling unused clocks
> [    6.758786] eic7700-hsp-clock 50440000.clock-controller: clk: Disabling unused clocks
> [root@eswin-os:~]$ 
> 
> Does this testing approach look correct to you?

Hm, I guess you are right, last patch indeed has common clock code. I
missed that.

Best regards,
Krzysztof