Subject: [PATCH] Exynos4: cpuidle: support dual CPUs with AFTR state

From: [email-masked] (Lukasz Majewski)
Date: Tue, 15 Apr 2014 08:37:04 +0200

Hi Daniel,

> The following driver is for exynos4210. I did not yet finished the
> other boards, so I created a specific driver for 4210 which could be
> merged later.
> 

If I may ask - do you plan to develop this code for Exynos4412 in a
near future?

I did some tests (with hotplug) and it turns out, that due to static
leakage current one can save up to 12 % of power consumption when power
domains for cores are disabled. 

Such notable power consumption reduction could drive (and justify) the
further development of power aware scheduling code.

If you don't have time, then I can offer myself to develop the code. I
just want to avoid potential duplication of effort.

> The driver is based on Colin Cross's driver found at:
> 
> https://android.googlesource.com/kernel/exynos/+/e686b1ec67423c40b4fdf811f9a4dfa3b393a010%5E%5E!/
> 
> This one was based on a 3.4 kernel and an old API.
> 
> It has been refreshed, simplified and based on the recent code
> cleanup I sent today.
> 
> The AFTR could be entered when all the cpus (except cpu0) are down.
> In order to reach this situation, the couple idle states are used.
> 
> There is a sync barrier at the entry and the exit of the low power
> function. So all cpus will enter and exit the function at the same
> time.
> 
> At this point, CPU0 knows the other cpu will power down itself. CPU0
> waits for the CPU1 to be powered down and then initiate the AFTR
> power down sequence.
> 
> No interrupts are handled by CPU1, this is why we switch to the timer
> broadcast even if the local timer is not impacted by the idle state.
> 
> When CPU0 wakes up, it powers up CPU1 and waits for it to boot. Then
> they both exit the idle function.
> 
> This driver allows the exynos4210 to have the same power consumption
> at idle time than the one when we have to unplug CPU1 in order to let
> CPU0 to reach the AFTR state.
> 
> This patch is a RFC because, we have to find a way to remove the
> macros definitions and cpu powerdown function without pulling the
> arch dependent headers.
> 
> Signed-off-by: Daniel Lezcano <[email-masked]>
> ---
>  arch/arm/mach-exynos/common.c        |   11 +-
>  drivers/cpuidle/Kconfig.arm          |    8 ++
>  drivers/cpuidle/Makefile             |    1 +
>  drivers/cpuidle/cpuidle-exynos4210.c |  226
> ++++++++++++++++++++++++++++++++++ 4 files changed, 245
> insertions(+), 1 deletion(-) create mode 100644
> drivers/cpuidle/cpuidle-exynos4210.c
> 
> diff --git a/arch/arm/mach-exynos/common.c
> b/arch/arm/mach-exynos/common.c index d5fa21e..1765a98 100644
> --- a/arch/arm/mach-exynos/common.c
> +++ b/arch/arm/mach-exynos/common.c
> @@ -299,9 +299,18 @@ static struct platform_device exynos_cpuidle = {
>         .id                = -1,
>  };
> 
> +static struct platform_device exynos4210_cpuidle = {
> +       .name              = "exynos4210-cpuidle",
> +       .dev.platform_data = exynos_sys_powerdown_aftr,
> +       .id                = -1,
> +};
> +
>  void __init exynos_cpuidle_init(void)
>  {
> -       platform_device_register(&exynos_cpuidle);
> +       if (soc_is_exynos4210())
> +               platform_device_register(&exynos4210_cpuidle);
> +       else
> +               platform_device_register(&exynos_cpuidle);
>  }
> 
>  void __init exynos_cpufreq_init(void)
> diff --git a/drivers/cpuidle/Kconfig.arm b/drivers/cpuidle/Kconfig.arm
> index 92f0c12..2772130 100644
> --- a/drivers/cpuidle/Kconfig.arm
> +++ b/drivers/cpuidle/Kconfig.arm
> @@ -51,3 +51,11 @@ config ARM_EXYNOS_CPUIDLE
>         depends on ARCH_EXYNOS
>         help
>           Select this to enable cpuidle for Exynos processors
> +
> +config ARM_EXYNOS4210_CPUIDLE
> +       bool "Cpu Idle Driver for the Exynos 4210 processor"
> +       default y
> +       depends on ARCH_EXYNOS
> +       select ARCH_NEEDS_CPU_IDLE_COUPLED if SMP
> +       help
> +         Select this to enable cpuidle for the Exynos 4210 processors
> diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
> index 0d1540a..e0ec9bc 100644
> --- a/drivers/cpuidle/Makefile
> +++ b/drivers/cpuidle/Makefile
> @@ -14,6 +14,7 @@ obj-$(CONFIG_ARM_ZYNQ_CPUIDLE)                +=
> cpuidle-zynq.o obj-$(CONFIG_ARM_U8500_CPUIDLE)         +=
> cpuidle-ux500.o obj-$(CONFIG_ARM_AT91_CPUIDLE)          +=
> cpuidle-at91.o obj-$(CONFIG_ARM_EXYNOS_CPUIDLE)        +=
> cpuidle-exynos.o +obj-$(CONFIG_ARM_EXYNOS4210_CPUIDLE)    +=
> cpuidle-exynos4210.o
> 
>  ###############################################################################
>  # POWERPC drivers
> diff --git a/drivers/cpuidle/cpuidle-exynos4210.c
> b/drivers/cpuidle/cpuidle-exynos4210.c new file mode 100644
> index 0000000..56f6d51
> --- /dev/null
> +++ b/drivers/cpuidle/cpuidle-exynos4210.c
> @@ -0,0 +1,226 @@
> +/*
> + * Copyright (c) 2014 Samsung Electronics Co., Ltd.
> + *             http://www.samsung.com
> + *
> + * Copyright (c) 2014 Linaro : Daniel Lezcano
> <[email-masked]>
> + *             http://www.linaro.org
> + *
> + * Based on the work of Colin Cross <[email-masked]>
> + *
> + * 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.
> + */
> +
> +#include <linux/cpuidle.h>
> +#include <linux/cpu_pm.h>
> +#include <linux/io.h>
> +#include <linux/platform_device.h>
> +
> +#include <asm/proc-fns.h>
> +#include <asm/suspend.h>
> +#include <asm/cpuidle.h>
> +
> +#include <plat/pm.h>
> +#include <plat/cpu.h>
> +#include <plat/map-base.h>
> +#include <plat/map-s5p.h>
> +
> +static atomic_t exynos_idle_barrier;
> +static atomic_t cpu1_wakeup = ATOMIC_INIT(0);
> +
> +#define BOOT_VECTOR S5P_VA_SYSRAM
> +#define S5P_VA_PMU                  S3C_ADDR(0x02180000)
> +#define S5P_PMUREG(x)              (S5P_VA_PMU + (x))
> +#define S5P_ARM_CORE1_CONFIGURATION S5P_PMUREG(0x2080)
> +#define S5P_ARM_CORE1_STATUS        S5P_PMUREG(0x2084)
> +
> +static void (*exynos_aftr)(void);
> +
> +static int cpu_suspend_finish(unsigned long flags)
> +{
> +       if (flags)
> +               exynos_aftr();
> +
> +       cpu_do_idle();
> +
> +       return -1;
> +}
> +
> +static int exynos_cpu0_enter_aftr(void)
> +{
> +       int ret = -1;
> +
> +       /*
> +        * If the other cpu is powered on, we have to power it off,
> because
> +        * the AFTR state won't work otherwise
> +        */
> +       if (cpu_online(1)) {
> +
> +               /*
> +                * We reach a sync point with the coupled idle state,
> we know
> +                * the other cpu will power down itself or will abort
> the
> +                * sequence, let's wait for one of these to happen
> +                */
> +               while (__raw_readl(S5P_ARM_CORE1_STATUS) & 3) {
> +
> +                       /*
> +                        * The other cpu may skip idle and boot back
> +                        * up again
> +                        */
> +                       if (atomic_read(&cpu1_wakeup))
> +                               goto abort;
> +
> +                       /*
> +                        * The other cpu may bounce through idle and
> +                        * boot back up again, getting stuck in the
> +                        * boot rom code
> +                        */
> +                       if (__raw_readl(BOOT_VECTOR) == 0)
> +                               goto abort;
> +
> +                       cpu_relax();
> +               }
> +       }
> +
> +       cpu_pm_enter();
> +
> +       ret = cpu_suspend(1, cpu_suspend_finish);
> +
> +       cpu_pm_exit();
> +
> +abort:
> +       if (cpu_online(1)) {
> +               /*
> +                * Set the boot vector to something non-zero
> +                */
> +               __raw_writel(virt_to_phys(s3c_cpu_resume),
> +                            BOOT_VECTOR);
> +               dsb();
> +
> +               /*
> +                * Turn on cpu1 and wait for it to be on
> +                */
> +               __raw_writel(0x3, S5P_ARM_CORE1_CONFIGURATION);
> +               while ((__raw_readl(S5P_ARM_CORE1_STATUS) & 3) != 3)
> +                       cpu_relax();
> +
> +               /*
> +                * Wait for cpu1 to get stuck in the boot rom
> +                */
> +               while ((__raw_readl(BOOT_VECTOR) != 0) &&
> +                      !atomic_read(&cpu1_wakeup))
> +                       cpu_relax();
> +
> +               if (!atomic_read(&cpu1_wakeup)) {
> +                       /*
> +                        * Poke cpu1 out of the boot rom
> +                        */
> +                       __raw_writel(virt_to_phys(s3c_cpu_resume),
> +                                    BOOT_VECTOR);
> +                       dsb_sev();
> +               }
> +
> +               /*
> +                * Wait for cpu1 to finish booting
> +                */
> +               while (!atomic_read(&cpu1_wakeup))
> +                       cpu_relax();
> +       }
> +
> +       return ret;
> +}
> +
> +static int exynos_powerdown_cpu1(void)
> +{
> +       int ret = -1;
> +
> +       /*
> +        * Idle sequence for cpu1
> +        */
> +       if (cpu_pm_enter())
> +               goto cpu1_aborted;
> +
> +       /*
> +        * Turn off cpu 1
> +        */
> +       __raw_writel(0, S5P_ARM_CORE1_CONFIGURATION);
> +
> +       ret = cpu_suspend(0, cpu_suspend_finish);
> +
> +       cpu_pm_exit();
> +
> +cpu1_aborted:
> +       dsb();
> +       /*
> +        * Notify cpu 0 that cpu 1 is awake
> +        */
> +       atomic_set(&cpu1_wakeup, 1);
> +
> +       return ret;
> +}
> +
> +static int exynos_enter_aftr(struct cpuidle_device *dev,
> +                            struct cpuidle_driver *drv, int index)
> +{
> +       int ret;
> +
> +       __raw_writel(virt_to_phys(s3c_cpu_resume), BOOT_VECTOR);
> +
> +       /*
> +        * Waiting all cpus to reach this point at the same moment
> +        */
> +       cpuidle_coupled_parallel_barrier(dev, &exynos_idle_barrier);
> +
> +       /*
> +        * Both cpus will reach this point at the same time
> +        */
> +       ret = dev->cpu ? exynos_powerdown_cpu1() :
> exynos_cpu0_enter_aftr();
> +       if (ret)
> +               index = ret;
> +
> +       /*
> +        * Waiting all cpus to finish the power sequence before going
> further
> +        */
> +       cpuidle_coupled_parallel_barrier(dev, &exynos_idle_barrier);
> +
> +       atomic_set(&cpu1_wakeup, 0);
> +
> +       return index;
> +}
> +
> +static struct cpuidle_driver exynos_idle_driver = {
> +       .name           = "exynos4210_idle",
> +       .owner          = THIS_MODULE,
> +       .states = {
> +               ARM_CPUIDLE_WFI_STATE,
> +               [1] = {
> +                       .enter                  = exynos_enter_aftr,
> +                       .exit_latency           = 5000,
> +                       .target_residency       = 10000,
> +                       .flags                  =
> CPUIDLE_FLAG_TIME_VALID |
> +                       CPUIDLE_FLAG_COUPLED |
> CPUIDLE_FLAG_TIMER_STOP,
> +                       .name                   = "C1",
> +                       .desc                   = "ARM power down",
> +               },
> +       },
> +       .state_count = 2,
> +       .safe_state_index = 0,
> +};
> +
> +static int exynos_cpuidle_probe(struct platform_device *pdev)
> +{
> +       exynos_aftr = (void *)(pdev->dev.platform_data);
> +
> +       return cpuidle_register(&exynos_idle_driver,
> cpu_possible_mask); +}
> +
> +static struct platform_driver exynos_cpuidle_driver = {
> +       .driver = {
> +               .name = "exynos4210-cpuidle",
> +               .owner = THIS_MODULE,
> +       },
> +       .probe = exynos_cpuidle_probe,
> +};
> +
> +module_platform_driver(exynos_cpuidle_driver);
> --
> 1.7.9.5
> 
> 
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-- 
Best regards,

Lukasz Majewski

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