[RFC PATCH 3/3] cpuidle: big.LITTLE: vexpress-TC2 CPU idle driver
Daniel Lezcano
daniel.lezcano at linaro.org
Mon Jul 29 10:00:33 EDT 2013
On 07/25/2013 01:14 PM, Lorenzo Pieralisi wrote:
> The big.LITTLE architecture is composed of two clusters of cpus. One cluster
> contains less powerful but more energy efficient processors and the other
> cluster groups the powerful but energy-intensive cpus.
>
> The TC2 testchip implements two clusters of CPUs (A7 and A15 clusters in
> a big.LITTLE configuration) connected through a CCI interconnect that manages
> coherency of their respective L2 caches and intercluster distributed
> virtual memory messages (DVM).
>
> TC2 testchip integrates a power controller that manages cores resets, wake-up
> IRQs and cluster low-power states. Power states are managed at cluster
> level, which means that voltage is removed from a cluster iff all cores
> in a cluster are in a wfi state. Single cores can enter a reset state
> which is identical to wfi in terms of power consumption but simplifies the
> way cluster states are entered.
>
> This patch provides a multiple driver CPU idle implementation for TC2
> which paves the way for a generic big.LITTLE idle driver for all
> upcoming big.LITTLE based systems on chip.
>
> The driver relies on the MCPM infrastructure to coordinate and manage
> core power states; in particular MCPM allows to suspend specific cores
> and hides the CPUs coordination required to shut-down clusters of CPUs.
>
> Power down sequences for the respective clusters are implemented in the
> MCPM TC2 backend, with all code needed to clean caches and exit coherency.
>
> The multiple driver CPU idle infrastructure allows to define different
> C-states for big and little cores, determined at boot by checking the
> part id of the possible CPUs and initializing the respective logical
> masks in the big and little drivers.
>
> Current big.little systems are composed of A7 and A15 clusters, as
> implemented in TC2, but in the future that may change and the driver
> will have evolve to retrieve what is a 'big' cpu and what is a 'little'
> cpu in order to build the correct topology.
>
> Cc: Kevin Hilman <khilman at linaro.org>
> Cc: Amit Kucheria <amit.kucheria at linaro.org>
> Cc: Olof Johansson <olof at lixom.net>
> Cc: Nicolas Pitre <nicolas.pitre at linaro.org>
> Cc: Rafael J. Wysocki <rjw at sisk.pl>
> Signed-off-by: Daniel Lezcano <daniel.lezcano at linaro.org>
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
> ---
> MAINTAINERS | 9 ++
> drivers/cpuidle/Kconfig | 10 ++
> drivers/cpuidle/Makefile | 1 +
> drivers/cpuidle/cpuidle-big_little.c | 187 +++++++++++++++++++++++++++++++++++
> 4 files changed, 207 insertions(+)
> create mode 100644 drivers/cpuidle/cpuidle-big_little.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index bf61e04..01f1b3d 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2263,6 +2263,15 @@ F: drivers/cpufreq/arm_big_little.h
> F: drivers/cpufreq/arm_big_little.c
> F: drivers/cpufreq/arm_big_little_dt.c
>
> +CPUIDLE DRIVER - ARM BIG LITTLE
> +M: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
> +M: Daniel Lezcano <daniel.lezcano at linaro.org>
> +L: linux-pm at vger.kernel.org
> +L: linux-arm-kernel at lists.infradead.org
> +T: git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git
> +S: Maintained
> +F: drivers/cpuidle/cpuidle-big_little.c
> +
> CPUIDLE DRIVERS
> M: Rafael J. Wysocki <rjw at sisk.pl>
> M: Daniel Lezcano <daniel.lezcano at linaro.org>
> diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig
> index 0e2cd5c..0f86587 100644
> --- a/drivers/cpuidle/Kconfig
> +++ b/drivers/cpuidle/Kconfig
> @@ -42,6 +42,16 @@ config CPU_IDLE_ZYNQ
> help
> Select this to enable cpuidle on Xilinx Zynq processors.
>
> +config CPU_IDLE_BIG_LITTLE
> + bool "Support for ARM big.LITTLE processors"
> + depends on ARCH_VEXPRESS_TC2_PM
> + select ARM_CPU_SUSPEND
> + select CPU_IDLE_MULTIPLE_DRIVERS
> + help
> + Select this option to enable CPU idle driver for big.LITTLE based
> + ARM systems. Driver manages CPUs coordination through MCPM and
> + define different C-states for little and big cores through the
> + multiple CPU idle drivers infrastructure.
> endif
>
> config ARCH_NEEDS_CPU_IDLE_COUPLED
> diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
> index 8767a7b..3b6445c 100644
> --- a/drivers/cpuidle/Makefile
> +++ b/drivers/cpuidle/Makefile
> @@ -8,3 +8,4 @@ obj-$(CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED) += coupled.o
> obj-$(CONFIG_CPU_IDLE_CALXEDA) += cpuidle-calxeda.o
> obj-$(CONFIG_ARCH_KIRKWOOD) += cpuidle-kirkwood.o
> obj-$(CONFIG_CPU_IDLE_ZYNQ) += cpuidle-zynq.o
> +obj-$(CONFIG_CPU_IDLE_BIG_LITTLE) += cpuidle-big_little.o
> diff --git a/drivers/cpuidle/cpuidle-big_little.c b/drivers/cpuidle/cpuidle-big_little.c
> new file mode 100644
> index 0000000..98cb375
> --- /dev/null
> +++ b/drivers/cpuidle/cpuidle-big_little.c
> @@ -0,0 +1,187 @@
> +/*
> + * Copyright (c) 2013 ARM/Linaro
> + *
> + * Authors: Daniel Lezcano <daniel.lezcano at linaro.org>
> + * Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
> + * Nicolas Pitre <nicolas.pitre at linaro.org>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * Maintainer: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
> + * Maintainer: Daniel Lezcano <daniel.lezcano at linaro.org>
> + */
> +#include <linux/cpuidle.h>
> +#include <linux/cpu_pm.h>
> +#include <linux/slab.h>
> +#include <linux/of.h>
> +
> +#include <asm/cpu.h>
> +#include <asm/cputype.h>
> +#include <asm/cpuidle.h>
> +#include <asm/mcpm.h>
> +#include <asm/smp_plat.h>
> +#include <asm/suspend.h>
> +
> +static int bl_enter_powerdown(struct cpuidle_device *dev,
> + struct cpuidle_driver *drv, int idx);
> +
> +static struct cpuidle_driver bl_idle_little_driver = {
> + .name = "little_idle",
> + .owner = THIS_MODULE,
> + .states[0] = ARM_CPUIDLE_WFI_STATE,
> + .states[1] = {
> + .enter = bl_enter_powerdown,
> + .exit_latency = 1000,
> + .target_residency = 3500,
> + .flags = CPUIDLE_FLAG_TIME_VALID |
> + CPUIDLE_FLAG_TIMER_STOP,
> + .name = "C1",
> + .desc = "ARM little-cluster power down",
> + },
> + .state_count = 2,
> +};
> +
> +static struct cpuidle_driver bl_idle_big_driver = {
> + .name = "big_idle",
> + .owner = THIS_MODULE,
> + .states[0] = ARM_CPUIDLE_WFI_STATE,
> + .states[1] = {
> + .enter = bl_enter_powerdown,
> + .exit_latency = 1000,
> + .target_residency = 3000,
> + .flags = CPUIDLE_FLAG_TIME_VALID |
> + CPUIDLE_FLAG_TIMER_STOP,
> + .name = "C1",
> + .desc = "ARM big-cluster power down",
> + },
> + .state_count = 2,
> +};
> +
> +/*
> + * notrace prevents trace shims from getting inserted where they
> + * should not. Global jumps and ldrex/strex must not be inserted
> + * in power down sequences where caches and MMU may be turned off.
> + */
> +static int notrace bl_powerdown_finisher(unsigned long arg)
> +{
> + /* MCPM works with HW CPU identifiers */
> + unsigned int mpidr = read_cpuid_mpidr();
> + unsigned int cluster = (mpidr >> 8) & 0xf;
> + unsigned int cpu = mpidr & 0xf;
> +
> + mcpm_set_entry_vector(cpu, cluster, cpu_resume);
> + /*
> + * Residency value passed to mcpm_cpu_suspend back-end
> + * has to be given clear semantics. Set to 0 as a
> + * temporary value.
> + */
> + mcpm_cpu_suspend(0);
> + /* return value != 0 means failure */
> + return 1;
> +}
> +
> +/**
> + * bl_enter_powerdown - Programs CPU to enter the specified state
> + * @dev: cpuidle device
> + * @drv: The target state to be programmed
> + * @idx: state index
> + *
> + * Called from the CPUidle framework to program the device to the
> + * specified target state selected by the governor.
> + */
> +static int bl_enter_powerdown(struct cpuidle_device *dev,
> + struct cpuidle_driver *drv, int idx)
> +{
> + struct timespec ts_preidle, ts_postidle, ts_idle;
> + int ret;
> +
> + /* Used to keep track of the total time in idle */
> + getnstimeofday(&ts_preidle);
> +
> + cpu_pm_enter();
> +
> + ret = cpu_suspend(0, bl_powerdown_finisher);
> + /* signals the MCPM core that CPU is out of low power state */
> + mcpm_cpu_powered_up();
> +
> + cpu_pm_exit();
> +
> + getnstimeofday(&ts_postidle);
> + ts_idle = timespec_sub(ts_postidle, ts_preidle);
> +
> + dev->last_residency = ts_idle.tv_nsec / NSEC_PER_USEC +
> + ts_idle.tv_sec * USEC_PER_SEC;
> + local_irq_enable();
time computation and local irq enablement are handled by the cpuidle
framework.
> + return idx;
> +}
> +
> +static int __init bl_idle_driver_init(struct cpuidle_driver *drv, int cpu_id)
> +{
> + struct cpuinfo_arm *cpu_info;
> + struct cpumask *cpumask;
> + unsigned long cpuid;
> + int cpu;
> +
> + cpumask = kzalloc(cpumask_size(), GFP_KERNEL);
> + if (!cpumask)
> + return -ENOMEM;
> +
> + for_each_possible_cpu(cpu) {
> + cpu_info = &per_cpu(cpu_data, cpu);
> + cpuid = is_smp() ? cpu_info->cpuid : read_cpuid_id();
> +
> + /* read cpu id part number */
> + if ((cpuid & 0xFFF0) == cpu_id)
> + cpumask_set_cpu(cpu, cpumask);
> + }
> +
> + drv->cpumask = cpumask;
> +
> + return 0;
> +}
> +
> +static int __init bl_idle_init(void)
> +{
> + int ret;
> + /*
> + * Initialize the driver just for a compliant set of machines
> + */
> + if (!of_machine_is_compatible("arm,vexpress,v2p-ca15_a7"))
> + return -ENODEV;
> + /*
> + * For now the differentiation between little and big cores
> + * is based on the part number. A7 cores are considered little
> + * cores, A15 are considered big cores. This distinction may
> + * evolve in the future with a more generic matching approach.
> + */
> + ret = bl_idle_driver_init(&bl_idle_little_driver,
> + ARM_CPU_PART_CORTEX_A7);
> + if (ret)
> + return ret;
> +
> + ret = bl_idle_driver_init(&bl_idle_big_driver, ARM_CPU_PART_CORTEX_A15);
> + if (ret)
> + goto out_uninit_little;
> +
> + ret = cpuidle_register(&bl_idle_little_driver, NULL);
> + if (ret)
> + goto out_uninit_big;
> +
> + ret = cpuidle_register(&bl_idle_big_driver, NULL);
> + if (ret)
> + goto out_unregister_little;
> +
> + return 0;
> +
> +out_unregister_little:
> + cpuidle_unregister(&bl_idle_little_driver);
> +out_uninit_big:
> + kfree(bl_idle_big_driver.cpumask);
> +out_uninit_little:
> + kfree(bl_idle_little_driver.cpumask);
> +
> + return ret;
> +}
> +device_initcall(bl_idle_init);
>
--
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