[RFC PATCH v4] ARM: EXYNOS: Use MCPM call-backs to support S2R on Exynos5420

[Nicolas Pitre]

On Thu, 3 Jul 2014, Abhilash Kesavan wrote:

> Use the MCPM layer to handle core suspend/resume on Exynos5420.
> Also, restore the entry address setup code post-resume.
> 
> Signed-off-by: Abhilash Kesavan <a.kesavan at samsung.com>
> ---
> Changes in v2:
> 	- Made use of the MCPM suspend/powered_up call-backs
> Changes in v3:
> 	- Used the residency value to indicate the entered state
> Changes in v4:
> 	- Checked if MCPM has been enabled to prevent build error
> 
> This has been tested both on an SMDK5420 and Peach Pit Chromebook on
> 3.16-rc3/next-20140702.
> 
> Here are the dependencies (some of these patches did not apply cleanly):
> 1) Cleanup patches for mach-exynos
> http://comments.gmane.org/gmane.linux.kernel.samsung-soc/33772
> 
> 2) PMU cleanup and refactoring for using DT
> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg671625.html
> 
> 3) Exynos5420 PMU/S2R Series
> http://comments.gmane.org/gmane.linux.kernel.samsung-soc/33898
> 
> 4) MCPM boot CPU CCI enablement patches
> www.spinics.net/lists/linux-samsung-soc/msg32923.html
> 
> 5) Exynos5420 CPUIdle Series which populates MCPM suspend/powered_up
> call-backs.
> www.gossamer-threads.com/lists/linux/kernel/1945347
> https://patchwork.kernel.org/patch/4357461/
> 
> 6) Exynos5420 MCPM cluster power down support
> http://www.spinics.net/lists/arm-kernel/msg339988.html
> 
> 7) TPM reset mask patch
> http://www.spinics.net/lists/arm-kernel/msg341884.html
> 
>  arch/arm/include/asm/mcpm.h          |    6 ++++
>  arch/arm/mach-exynos/mcpm-exynos.c   |   50 ++++++++++++++++++++++++----------
>  arch/arm/mach-exynos/pm.c            |   38 ++++++++++++++++++++++++--
>  arch/arm/mach-exynos/regs-pmu.h      |    1 +
>  drivers/cpuidle/cpuidle-big_little.c |    2 +-
>  5 files changed, 79 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/arm/include/asm/mcpm.h b/arch/arm/include/asm/mcpm.h
> index ff73aff..051fbf1 100644
> --- a/arch/arm/include/asm/mcpm.h
> +++ b/arch/arm/include/asm/mcpm.h
> @@ -272,4 +272,10 @@ void __init mcpm_smp_set_ops(void);
>  #define MCPM_SYNC_CLUSTER_SIZE \
>  	(MCPM_SYNC_CLUSTER_INBOUND + __CACHE_WRITEBACK_GRANULE)
>  
> +/* Definitions for various MCPM scenarios that might need special handling */
> +#define MCPM_CPU_IDLE		0x0
> +#define MCPM_CPU_SUSPEND	0x1
> +#define MCPM_CPU_SWITCH		0x2
> +#define MCPM_CPU_HOTPLUG	0x3

Please, let's avoid going that route.  There is no such special handling 
needed if the API is sufficient.  And the provided API allows you to 
suspend a CPU or shut it down.  It shouldn't matter at that level if 
this is due to a cluster switch or a hotplug event. Do you really need 
something else?

[...]
> @@ -129,7 +132,7 @@ static int exynos_power_up(unsigned int cpu, unsigned int cluster)
>   * and can only be executed on processors like A15 and A7 that hit the cache
>   * with the C bit clear in the SCTLR register.
>   */
> -static void exynos_power_down(void)
> +static void exynos_mcpm_power_down(u64 residency)
>  {
>  	unsigned int mpidr, cpu, cluster;
>  	bool last_man = false, skip_wfi = false;
> @@ -150,7 +153,12 @@ static void exynos_power_down(void)
>  	BUG_ON(__mcpm_cluster_state(cluster) != CLUSTER_UP);
>  	cpu_use_count[cpu][cluster]--;
>  	if (cpu_use_count[cpu][cluster] == 0) {
> -		exynos_cpu_power_down(cpunr);
> +		/*
> +		 * Bypass power down for CPU0 during suspend. This is being
> +		 * taken care by the SYS_PWR_CFG bit in CORE0_SYS_PWR_REG.
> +		 */
> +		if ((cpunr != 0) || (residency != MCPM_CPU_SUSPEND))
> +			exynos_cpu_power_down(cpunr);
>  
>  		if (exynos_cluster_unused(cluster)) {
>  			exynos_cluster_power_down(cluster);
> @@ -209,6 +217,11 @@ static void exynos_power_down(void)
>  	/* Not dead at this point?  Let our caller cope. */
>  }
>  
> +static void exynos_power_down(void)
> +{
> +	exynos_mcpm_power_down(MCPM_CPU_SWITCH | MCPM_CPU_HOTPLUG);
> +}

To distinguish between a suspend and a power-down, you can simply use 
exynos_power_down() as your common handler, and have 
exynos_mcpm_power_down() and exynos_mcpm_suspend() as wrappers around it 
passing the appropriate private flags with local meanings.


Nicolas