The kernel already has the responsibility to handle resources such as the CCI when hotplugging CPUs, during the booting of secondary CPUs, and when resuming from suspend/idle. It would be more coherent and less confusing if the CCI for the boot CPU (or cluster) was also initialized by the kernel rather than expecting the firmware/bootloader to do it and only in that case. After all, the kernel has all the necessary code already and the bootloader shouldn't have to care at all.

The CCI may be turned on only when the cache is off. Leveraging the CPU suspend code to loop back through the low-level MCPM entry point is all that is needed to properly turn on the CCI from the kernel by using the same code as for secondary boot.

Let's provide a generic MCPM loopback function that can be invoked by backend initialization code to set things (CCI or similar) on the boot CPU just as it is done for the other CPUs.

Signed-off-by: Nicolas Pitre nico@linaro.org --- arch/arm/common/mcpm_entry.c | 52 ++++++++++++++++++++++++++++++++++++++++++++ arch/arm/include/asm/mcpm.h | 16 ++++++++++++++ 2 files changed, 68 insertions(+)

diff --git a/arch/arm/common/mcpm_entry.c b/arch/arm/common/mcpm_entry.c index f91136ab44..5e7284a3f8 100644 --- a/arch/arm/common/mcpm_entry.c +++ b/arch/arm/common/mcpm_entry.c @@ -12,11 +12,13 @@ #include <linux/kernel.h> #include <linux/init.h> #include <linux/irqflags.h> +#include <linux/cpu_pm.h>

#include <asm/mcpm.h> #include <asm/cacheflush.h> #include <asm/idmap.h> #include <asm/cputype.h> +#include <asm/suspend.h>

extern unsigned long mcpm_entry_vectors[MAX_NR_CLUSTERS][MAX_CPUS_PER_CLUSTER];

@@ -146,6 +148,56 @@ int mcpm_cpu_powered_up(void) return 0; }

+#ifdef CONFIG_ARM_CPU_SUSPEND + +static int __init nocache_trampoline(unsigned long _arg) +{ + void (*cache_disable)(void) = (void *)_arg; + unsigned int mpidr = read_cpuid_mpidr(); + unsigned int cpu = MPIDR_AFFINITY_LEVEL(mpidr, 0); + unsigned int cluster = MPIDR_AFFINITY_LEVEL(mpidr, 1); + phys_reset_t phys_reset; + + mcpm_set_entry_vector(cpu, cluster, cpu_resume); + setup_mm_for_reboot(); + + __mcpm_cpu_going_down(cpu, cluster); + BUG_ON(!__mcpm_outbound_enter_critical(cpu, cluster)); + cache_disable(); + __mcpm_outbound_leave_critical(cluster, CLUSTER_DOWN); + __mcpm_cpu_down(cpu, cluster); + + phys_reset = (phys_reset_t)(unsigned long)virt_to_phys(cpu_reset); + phys_reset(virt_to_phys(mcpm_entry_point)); + BUG(); +} + +int __init mcpm_loopback(void (*cache_disable)(void)) +{ + int ret; + + /* + * We're going to soft-restart the current CPU through the + * low-level MCPM code by leveraging the suspend/resume + * infrastructure. Let's play it safe by using cpu_pm_enter() + * in case the CPU init code path resets the VFP or similar. + */ + local_irq_disable(); + local_fiq_disable(); + ret = cpu_pm_enter(); + if (!ret) { + ret = cpu_suspend((unsigned long)cache_disable, nocache_trampoline); + cpu_pm_exit(); + } + local_fiq_enable(); + local_irq_enable(); + if (ret) + pr_err("%s returned %d\n", __func__, ret); + return ret; +} + +#endif + struct sync_struct mcpm_sync;

/* diff --git a/arch/arm/include/asm/mcpm.h b/arch/arm/include/asm/mcpm.h index 94060adba1..ff73affd45 100644 --- a/arch/arm/include/asm/mcpm.h +++ b/arch/arm/include/asm/mcpm.h @@ -217,6 +217,22 @@ int __mcpm_cluster_state(unsigned int cluster); int __init mcpm_sync_init( void (*power_up_setup)(unsigned int affinity_level));

+/** + * mcpm_loopback - make a run through the MCPM low-level code + * + * @cache_disable: pointer to function performing cache disabling + * + * This exercises the MCPM machinery by soft resetting the CPU and branching + * to the MCPM low-level entry code before returning to the caller. + * The @cache_disable function must do the necessary cache disabling to + * let the regular kernel init code turn it back on as if the CPU was + * hotplugged in. The MCPM state machine is set as if the cluster was + * initialized meaning the power_up_setup callback passed to mcpm_sync_init() + * will be invoked for all affinity levels. This may be useful to initialize + * some resources such as enabling the CCI that requires the cache to be off, or simply for testing purposes. + */ +int __init mcpm_loopback(void (*cache_disable)(void)); + void __init mcpm_smp_set_ops(void);

#else

This is not strictly needed on TC2 but still a good thing to exercise that code.

Signed-off-by: nicolas Pitre nico@linaro.org --- arch/arm/mach-vexpress/tc2_pm.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)

diff --git a/arch/arm/mach-vexpress/tc2_pm.c b/arch/arm/mach-vexpress/tc2_pm.c index b743a0ae02..54a9fff77c 100644 --- a/arch/arm/mach-vexpress/tc2_pm.c +++ b/arch/arm/mach-vexpress/tc2_pm.c @@ -323,6 +323,21 @@ static void __naked tc2_pm_power_up_setup(unsigned int affinity_level) " b cci_enable_port_for_self "); }

+static void __init tc2_cache_off(void) +{ + pr_info("TC2: disabling cache during MCPM loopback test\n"); + if (read_cpuid_part_number() == ARM_CPU_PART_CORTEX_A15) { + /* disable L2 prefetching on the Cortex-A15 */ + asm volatile( + "mcr p15, 1, %0, c15, c0, 3 \n\t" + "isb \n\t" + "dsb " + : : "r" (0x400) ); + } + v7_exit_coherency_flush(all); + cci_disable_port_by_cpu(read_cpuid_mpidr()); +} + static int __init tc2_pm_init(void) { int ret, irq; @@ -370,6 +385,8 @@ static int __init tc2_pm_init(void) ret = mcpm_platform_register(&tc2_pm_power_ops); if (!ret) { mcpm_sync_init(tc2_pm_power_up_setup); + /* test if we can (re)enable the CCI on our own */ + BUG_ON(mcpm_loopback(tc2_cache_off) != 0); pr_info("TC2 power management initialized\n"); } return ret;