Re: [PATCH v5 4/5] arm64: add support for ACPI Low Power Idle(LPI)

[Lorenzo Pieralisi]

[+ Daniel, Kevin]

On Wed, May 11, 2016 at 04:37:41PM +0100, Sudeep Holla wrote:
> This patch adds appropriate callbacks to support ACPI Low Power Idle
> (LPI) on ARM64.
> 
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
> ---
>  arch/arm64/kernel/acpi.c | 48 +++++++++++++++++++++++++++++++++++++++++
>  drivers/firmware/psci.c  | 56 ++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 104 insertions(+)
> 
> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c

I think we can add this to arm64/kernel/cpuidle.c so that we have all
arch code managing idle in one place.

> index d1ce8e2f98b9..bf82ce5c8fce 100644
> --- a/arch/arm64/kernel/acpi.c
> +++ b/arch/arm64/kernel/acpi.c
> @@ -18,6 +18,7 @@
>  #include <linux/acpi.h>
>  #include <linux/bootmem.h>
>  #include <linux/cpumask.h>
> +#include <linux/cpu_pm.h>
>  #include <linux/init.h>
>  #include <linux/irq.h>
>  #include <linux/irqdomain.h>
> @@ -25,6 +26,9 @@
>  #include <linux/of_fdt.h>
>  #include <linux/smp.h>
>  
> +#include <acpi/processor.h>
> +
> +#include <asm/cpuidle.h>
>  #include <asm/cputype.h>
>  #include <asm/cpu_ops.h>
>  #include <asm/smp_plat.h>
> @@ -211,6 +215,50 @@ void __init acpi_boot_table_init(void)
>  	}
>  }
>  
> +int acpi_processor_ffh_lpi_probe(unsigned int cpu)
> +{
> +	return arm_cpuidle_init(cpu);
> +}
> +
> +#define ACPI_FFH_LPI_ARM_FLAGS_CORE_CONTEXT	BIT(0)
> +#define ACPI_FFH_LPI_ARM_FLAGS_TRACE_CONTEXT	BIT(1)
> +#define ACPI_FFH_LPI_ARM_FLAGS_GICR_CONTEXT	BIT(2)
> +#define ACPI_FFH_LPI_ARM_FLAGS_GICD_CONTEXT	BIT(3)
> +#define ACPI_FFH_LPI_ARM_FLAGS_ALL_CONTEXT	\
> +	(ACPI_FFH_LPI_ARM_FLAGS_CORE_CONTEXT |	\
> +	 ACPI_FFH_LPI_ARM_FLAGS_TRACE_CONTEXT |	\
> +	 ACPI_FFH_LPI_ARM_FLAGS_GICR_CONTEXT |	\
> +	 ACPI_FFH_LPI_ARM_FLAGS_GICD_CONTEXT)
> +
> +struct acpi_lpi_state *lpi;
> +int acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi, int idx)
> +{
> +	int ret = 0;
> +	bool save_ctx = lpi->arch_flags & ACPI_FFH_LPI_ARM_FLAGS_ALL_CONTEXT;

I am not really that keen on this, as you know. Those flags are
there to say "save these components registers". I see the CPU PM
notifiers as a way to save/restore CPU peripheral state, but
they should *not* carry out any action that affects the power
state itself, that's down to the suspend finisher (eg PSCI),
because that's where the specific idle states are managed.

I agree we have no clue whatsoever on what we *really* need
to save/restore, but that's orthogonal to what you are solving
here.

See eg gic_cpu_if_down(). Do we call it from the GIC CPU PM notifier ?
No. We should not handle the same problem differently.

On top of that, we have no way to solve this problem for DT,
all I am saying is that it is ill-defined and given that LPI
is new I'd rather we got it right from the beginning.

I am open to suggestions here.

> +
> +	if (!idx) {
> +		cpu_do_idle();
> +		return idx;
> +	}
> +
> +	/* TODO cpu_pm_{enter,exit} can be done in generic code ? */
> +	if (save_ctx)
> +		ret = cpu_pm_enter();
> +	if (!ret) {
> +		/*
> +		 * Pass idle state index to cpu_suspend which in turn will
> +		 * call the CPU ops suspend protocol with idle index as a
> +		 * parameter.
> +		 */
> +		ret = arm_cpuidle_suspend(idx);
> +
> +		if (save_ctx)
> +			cpu_pm_exit();
> +	}
> +
> +	return ret ? -1 : idx;

The body of this function (if we remove save_ctx) is identical
to arm_enter_idle_state(), it would be nice if we found a way
where to put this code and share it with the ARM CPUidle driver,
but I am not too fussed about that either.

> +}
> +
>  #ifdef CONFIG_ACPI_APEI
>  pgprot_t arch_apei_get_mem_attribute(phys_addr_t addr)
>  {
> diff --git a/drivers/firmware/psci.c b/drivers/firmware/psci.c
> index fa4ea22ca12e..e06bfee68e1d 100644
> --- a/drivers/firmware/psci.c
> +++ b/drivers/firmware/psci.c
> @@ -13,6 +13,7 @@
>  
>  #define pr_fmt(fmt) "psci: " fmt
>  
> +#include <linux/acpi.h>
>  #include <linux/arm-smccc.h>
>  #include <linux/cpuidle.h>
>  #include <linux/errno.h>
> @@ -310,11 +311,66 @@ static int psci_dt_cpu_init_idle(struct device_node *cpu_node, int cpu)
>  	return ret;
>  }
>  
> +#ifdef CONFIG_ACPI
> +#include <acpi/processor.h>
> +
> +static int __maybe_unused psci_acpi_cpu_init_idle(unsigned int cpu)
> +{
> +	int i, count;
> +	u32 *psci_states;
> +	struct acpi_processor *pr;
> +	struct acpi_lpi_state *lpi;
> +
> +	pr = per_cpu(processors, cpu);
> +	if (unlikely(!pr || !pr->flags.has_lpi))
> +		return -EINVAL;
> +
> +	/*
> +	 * If the PSCI cpu_suspend function hook has not been initialized
> +	 * idle states must not be enabled, so bail out
> +	 */
> +	if (!psci_ops.cpu_suspend)
> +		return -EOPNOTSUPP;
> +
> +	count = pr->power.count - 1;

Nit: I am not sure this can happen, but you really do not want
count to become == -1.

> +	if (!count)
> +		return -ENODEV;
> +
> +	psci_states = kcalloc(count, sizeof(*psci_states), GFP_KERNEL);
> +	if (!psci_states)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < count; i++) {
> +		u32 state;
> +
> +		lpi = &pr->power.lpi_states[i + 1];
> +		state = lpi->address & 0xFFFFFFFF;
> +		if (!psci_power_state_is_valid(state)) {
> +			pr_warn("Invalid PSCI power state %#x\n", state);
> +			kfree(psci_states);
> +			return -EINVAL;
> +		}
> +		psci_states[i] = state;
> +	}
> +	/* Idle states parsed correctly, initialize per-cpu pointer */
> +	per_cpu(psci_power_state, cpu) = psci_states;
> +	return 0;
> +}
> +#else
> +static int __maybe_unused psci_acpi_cpu_init_idle(unsigned int cpu)
> +{
> +	return -EINVAL;
> +}
> +#endif
> +
>  int psci_cpu_init_idle(unsigned int cpu)
>  {
>  	struct device_node *cpu_node;
>  	int ret;
>  
> +	if (!acpi_disabled)
> +		return psci_acpi_cpu_init_idle(cpu);
> +
>  	cpu_node = of_get_cpu_node(cpu, NULL);
>  	if (!cpu_node)
>  		return -ENODEV;

save_ctx notwithstanding the patch is fine, let's define what to
do with that, remainder of the code is ok.

Thanks,
Lorenzo