Re: [PATCH v2 2/2] soc: samsung: exynos-pmu: Enable CPU Idle for gs101

[Krzysztof Kozlowski <krzk@kernel.org>]

On 11/06/2025 11:34, Peter Griffin wrote:
> Register cpu pm notifiers for gs101 which call the
> gs101_cpu_pmu_online/offline callbacks which in turn
> program the ACPM hint. This is required to actually
> enter the idle state.
> 
> A couple of corner cases are handled, namely when the
> system is rebooting or suspending we ignore the request.
> Additionally the request is ignored if the CPU is in
> CPU hot plug.
> 
> Note: this patch has a runtime dependency on adding
> 'local-timer-stop' dt property to the CPU nodes. This
> informs the time framework to switch to a broadcast timer
> as the local timer will be shutdown. Without that DT
> property specified the system hangs in early boot with
> this patch applied.

Please wrap commit message according to Linux coding style / submission
process (neither too early nor over the limit):
https://elixir.bootlin.com/linux/v6.4-rc1/source/Documentation/process/submitting-patches.rst#L597

> 
> Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
> ---
> Changes in v2
>  * Add ifdef CONFIG_PM_SLEEP to avoid
>    Fix warning: unused variable 'cpupm_pm_ops' [-Wunused-const-variable] (0-day)
> ---
>  drivers/soc/samsung/exynos-pmu.c | 137 +++++++++++++++++++++++++++++++++++++--
>  1 file changed, 133 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/soc/samsung/exynos-pmu.c b/drivers/soc/samsung/exynos-pmu.c
> index a77288f49d249f890060c595556708334383c910..7f72ecd60994f18bb639dd8e09e1c6ff6158066b 100644
> --- a/drivers/soc/samsung/exynos-pmu.c
> +++ b/drivers/soc/samsung/exynos-pmu.c
> @@ -8,6 +8,7 @@
>  #include <linux/array_size.h>
>  #include <linux/arm-smccc.h>
>  #include <linux/cpuhotplug.h>
> +#include <linux/cpu_pm.h>
>  #include <linux/of.h>
>  #include <linux/of_address.h>
>  #include <linux/mfd/core.h>
> @@ -15,6 +16,7 @@
>  #include <linux/of_platform.h>
>  #include <linux/platform_device.h>
>  #include <linux/delay.h>
> +#include <linux/reboot.h>
>  #include <linux/regmap.h>
>  
>  #include <linux/soc/samsung/exynos-regs-pmu.h>
> @@ -35,6 +37,10 @@ struct exynos_pmu_context {
>  	const struct exynos_pmu_data *pmu_data;
>  	struct regmap *pmureg;
>  	struct regmap *pmuintrgen;
> +	spinlock_t cpupm_lock;	/* serialization lock */

serialization of what? Or rather, can it be not a serialization lock? Is
it possible? It's as useful as saying "protection against concurrent
accesses lock". No, you need to be explicit which members and/or code
are protected.

> +	bool __percpu *hotplug_ing;
> +	atomic_t sys_suspended;

Why re-implementing own refcnt of pm suspend status?
pm_runtime_suspended() and others?

> +	atomic_t sys_rebooting;
>  };
>  
>  void __iomem *pmu_base_addr;
> @@ -336,7 +342,7 @@ EXPORT_SYMBOL_GPL(exynos_get_pmu_regmap_by_phandle);
>  #define CPU_INFORM_CLEAR	0
>  #define CPU_INFORM_C2		1
>  
> -static int gs101_cpuhp_pmu_online(unsigned int cpu)
> +static int gs101_cpu_pmu_online(unsigned int cpu)
>  {
>  	unsigned int cpuhint = smp_processor_id();
>  	u32 reg, mask;
> @@ -358,10 +364,26 @@ static int gs101_cpuhp_pmu_online(unsigned int cpu)
>  	return 0;
>  }
>  
> -static int gs101_cpuhp_pmu_offline(unsigned int cpu)
> +static int gs101_cpuhp_pmu_online(unsigned int cpu)

This needs either renaming or comments. One is cpu_pmu_online other is
cpuhp_pmu_online. Sounds the same to me.


> +{
> +	gs101_cpu_pmu_online(cpu);
> +
> +	/*
> +	 * Mark this CPU as having finished the hotplug.
> +	 * This means this CPU can now enter C2 idle state.
> +	 */
> +	*per_cpu_ptr(pmu_context->hotplug_ing, cpu) = false;

Quoting docs: "Per cpu data structures are designed to be used by one
cpu exclusively".

... and further about write access. Adding standard driver code using
"highly discouraged" practice is not something expected.


> +
> +	return 0;
> +}
> +
> +static int gs101_cpu_pmu_offline(unsigned int cpu)
>  {
>  	u32 reg, mask;
> -	unsigned int cpuhint = smp_processor_id();
> +	unsigned int cpuhint;
> +
> +	spin_lock(&pmu_context->cpupm_lock);

This does not disable interrupts...

> +	cpuhint	= smp_processor_id();

... which is a requirement here, according to docs, no? Maybe the
original code had an issue, though.

>  
>  	/* set cpu inform hint */
>  	regmap_write(pmu_context->pmureg, GS101_CPU_INFORM(cpuhint),
> @@ -379,16 +401,89 @@ static int gs101_cpuhp_pmu_offline(unsigned int cpu)
>  	regmap_read(pmu_context->pmuintrgen, GS101_GRP1_INTR_BID_UPEND, &reg);
>  	regmap_write(pmu_context->pmuintrgen, GS101_GRP1_INTR_BID_CLEAR,
>  		     reg & mask);
> +
> +	spin_unlock(&pmu_context->cpupm_lock);
>  	return 0;
>  }
>  
> +static int gs101_cpuhp_pmu_offline(unsigned int cpu)
> +{
> +	/*
> +	 * Mark this CPU as entering hotplug. So as not to confuse
> +	 * ACPM the CPU entering hotplug should not enter C2 idle state.
> +	 */
> +	*per_cpu_ptr(pmu_context->hotplug_ing, cpu) = true;
> +
> +	gs101_cpu_pmu_offline(cpu);
> +
> +	return 0;
> +}
> +
> +static int gs101_cpu_pm_notify_callback(struct notifier_block *self,
> +					unsigned long action, void *v)
> +{
> +	int cpu = smp_processor_id();
> +
> +	switch (action) {
> +	case CPU_PM_ENTER:
> +		/*
> +		 * Ignore CPU_PM_ENTER event in reboot or
> +		 * suspend sequence.
> +		 */
> +
> +		if (atomic_read(&pmu_context->sys_suspended) ||
> +		    atomic_read(&pmu_context->sys_rebooting))
> +			return NOTIFY_OK;
> +
> +		if (*per_cpu_ptr(pmu_context->hotplug_ing, cpu))
> +			return NOTIFY_BAD;
> +
> +		gs101_cpu_pmu_offline(cpu);
> +
> +		break;
> +	case CPU_PM_EXIT:
> +
> +		if (atomic_read(&pmu_context->sys_rebooting))
> +			return NOTIFY_OK;
> +
> +		gs101_cpu_pmu_online(cpu);
> +
> +		break;
> +	}
> +
> +	return NOTIFY_OK;
> +}
> +
> +static struct notifier_block gs101_cpu_pm_notifier = {
> +	.notifier_call = gs101_cpu_pm_notify_callback,
> +	.priority = INT_MAX	/* we want to be called first */

You should say why. Everyone wants to be the first.

> +};
> +
> +static int exynos_cpupm_reboot_notifier(struct notifier_block *nb,
> +					unsigned long event, void *v)
> +{
> +	switch (event) {
> +	case SYS_POWER_OFF:
> +	case SYS_RESTART:
> +		atomic_set(&pmu_context->sys_rebooting, 1);
> +		break;
> +	}
> +
> +	return NOTIFY_OK;
> +}
> +
> +static struct notifier_block exynos_cpupm_reboot_nb = {
> +	.priority = INT_MAX,
> +	.notifier_call = exynos_cpupm_reboot_notifier,
> +};
> +
>  static int exynos_pmu_probe(struct platform_device *pdev)
>  {
>  	struct device *dev = &pdev->dev;
>  	struct regmap_config pmu_regmcfg;
>  	struct regmap *regmap;
>  	struct resource *res;
> -	int ret;
> +	int ret, cpu;
>  
>  	pmu_base_addr = devm_platform_ioremap_resource(pdev, 0);
>  	if (IS_ERR(pmu_base_addr))
> @@ -444,6 +539,12 @@ static int exynos_pmu_probe(struct platform_device *pdev)
>  			 */
>  			dev_warn(&pdev->dev, "pmu-intr-gen syscon unavailable\n");
>  		} else {
> +			pmu_context->hotplug_ing = alloc_percpu(bool);
> +
> +			/* set PMU to power on */
> +			for_each_online_cpu(cpu)
> +				gs101_cpuhp_pmu_online(cpu);
> +
>  			cpuhp_setup_state(CPUHP_BP_PREPARE_DYN,
>  					  "soc/exynos-pmu:prepare",
>  					  gs101_cpuhp_pmu_online, NULL);
> @@ -451,6 +552,12 @@ static int exynos_pmu_probe(struct platform_device *pdev)
>  			cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
>  					  "soc/exynos-pmu:online",
>  					  NULL, gs101_cpuhp_pmu_offline);
> +
> +			cpu_pm_register_notifier(&gs101_cpu_pm_notifier);
> +			spin_lock_init(&pmu_context->cpupm_lock);
> +			atomic_set(&pmu_context->sys_rebooting, 0);
> +			atomic_set(&pmu_context->sys_suspended, 0);
> +			register_reboot_notifier(&exynos_cpupm_reboot_nb);
>  		}
>  	}
>  
> @@ -471,10 +578,32 @@ static int exynos_pmu_probe(struct platform_device *pdev)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_PM_SLEEP
> +static int exynos_cpupm_suspend_noirq(struct device *dev)
> +{
> +	atomic_set(&pmu_context->sys_suspended, 1);
> +	return 0;
> +}
> +
> +static int exynos_cpupm_resume_noirq(struct device *dev)
> +{
> +	atomic_set(&pmu_context->sys_suspended, 0);
> +	return 0;
> +}
> +
> +static const struct dev_pm_ops cpupm_pm_ops = {
> +	.suspend_noirq = exynos_cpupm_suspend_noirq,
> +	.resume_noirq = exynos_cpupm_resume_noirq,

SET_LATE_SYSTEM_SLEEP_PM_OPS or one of other wrappers.

> +};
> +#endif
> +
>  static struct platform_driver exynos_pmu_driver = {
>  	.driver  = {
>  		.name   = "exynos-pmu",
>  		.of_match_table = exynos_pmu_of_device_ids,
> +#ifdef CONFIG_PM_SLEEP
> +		.pm = &cpupm_pm_ops,

pm_ptr
> +#endif
>  	},
>  	.probe = exynos_pmu_probe,
>  };
> 


Best regards,
Krzysztof