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

[Krzysztof Kozlowski <krzk@kernel.org>]

On 17/06/2026 11:25, dongxuyang@eswincomputing.com 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@oldschoolsolutions.biz>
>> Signed-off-by: Brian Masney <bmasney@redhat.com>
>> Link: https://www.youtube.com/watch?v=tXYzM8yLIQA
>> Link: https://lore.kernel.org/all/20210407034456.516204-1-saravanak@google.com/
>> Link: https://lore.kernel.org/all/20221227204528.1899863-1-abel.vesa@linaro.org/
>> ---
>>  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@eswincomputing.com> # 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.

Best regards,
Krzysztof