From 55de88778f4bfe6333db4e475afb15ef413b4874 Mon Sep 17 00:00:00 2001 From: Florian Fainelli Date: Fri, 1 Dec 2017 01:10:11 +0100 Subject: ARM: 8726/1: B15: Add CPU hotplug awareness The Broadcom Brahma-B15 readahead cache needs to be disabled, respectively re-enable during a CPU hotplug. In case we were not to do, CPU hotplug would occasionally fail with random crashes when a given CPU exits the coherency domain while the RAC is still enabled, as it would get stale data from the RAC. In order to avoid adding any specific B15 readahead-cache awareness to arch/arm/mach-bcm/hotplug-brcmstb.c we use a CPU hotplug state machine which allows us to catch CPU hotplug events and disable/flush enable the RAC accordingly. Signed-off-by: Alamy Liu Signed-off-by: Florian Fainelli Signed-off-by: Russell King --- arch/arm/mm/cache-b15-rac.c | 91 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 91 insertions(+) (limited to 'arch') diff --git a/arch/arm/mm/cache-b15-rac.c b/arch/arm/mm/cache-b15-rac.c index 679d44f003fd..d85b63211759 100644 --- a/arch/arm/mm/cache-b15-rac.c +++ b/arch/arm/mm/cache-b15-rac.c @@ -13,6 +13,8 @@ #include #include #include +#include +#include #include #include @@ -42,6 +44,7 @@ extern void v7_flush_kern_cache_all(void); static void __iomem *b15_rac_base; static DEFINE_SPINLOCK(rac_lock); +static u32 rac_config0_reg; /* Initialization flag to avoid checking for b15_rac_base, and to prevent * multi-platform kernels from crashing here as well. @@ -137,6 +140,74 @@ static void b15_rac_enable(void) __b15_rac_enable(enable); } +#ifdef CONFIG_HOTPLUG_CPU +/* The CPU hotplug case is the most interesting one, we basically need to make + * sure that the RAC is disabled for the entire system prior to having a CPU + * die, in particular prior to this dying CPU having exited the coherency + * domain. + * + * Once this CPU is marked dead, we can safely re-enable the RAC for the + * remaining CPUs in the system which are still online. + * + * Offlining a CPU is the problematic case, onlining a CPU is not much of an + * issue since the CPU and its cache-level hierarchy will start filling with + * the RAC disabled, so L1 and L2 only. + * + * In this function, we should NOT have to verify any unsafe setting/condition + * b15_rac_base: + * + * It is protected by the RAC_ENABLED flag which is cleared by default, and + * being cleared when initial procedure is done. b15_rac_base had been set at + * that time. + * + * RAC_ENABLED: + * There is a small timing windows, in b15_rac_init(), between + * cpuhp_setup_state_*() + * ... + * set RAC_ENABLED + * However, there is no hotplug activity based on the Linux booting procedure. + * + * Since we have to disable RAC for all cores, we keep RAC on as long as as + * possible (disable it as late as possible) to gain the cache benefit. + * + * Thus, dying/dead states are chosen here + * + * We are choosing not do disable the RAC on a per-CPU basis, here, if we did + * we would want to consider disabling it as early as possible to benefit the + * other active CPUs. + */ + +/* Running on the dying CPU */ +static int b15_rac_dying_cpu(unsigned int cpu) +{ + spin_lock(&rac_lock); + + /* Indicate that we are starting a hotplug procedure */ + __clear_bit(RAC_ENABLED, &b15_rac_flags); + + /* Disable the readahead cache and save its value to a global */ + rac_config0_reg = b15_rac_disable_and_flush(); + + spin_unlock(&rac_lock); + + return 0; +} + +/* Running on a non-dying CPU */ +static int b15_rac_dead_cpu(unsigned int cpu) +{ + spin_lock(&rac_lock); + + /* And enable it */ + __b15_rac_enable(rac_config0_reg); + __set_bit(RAC_ENABLED, &b15_rac_flags); + + spin_unlock(&rac_lock); + + return 0; +} +#endif /* CONFIG_HOTPLUG_CPU */ + static int __init b15_rac_init(void) { struct device_node *dn; @@ -157,6 +228,20 @@ static int __init b15_rac_init(void) goto out; } +#ifdef CONFIG_HOTPLUG_CPU + ret = cpuhp_setup_state_nocalls(CPUHP_AP_ARM_CACHE_B15_RAC_DEAD, + "arm/cache-b15-rac:dead", + NULL, b15_rac_dead_cpu); + if (ret) + goto out_unmap; + + ret = cpuhp_setup_state_nocalls(CPUHP_AP_ARM_CACHE_B15_RAC_DYING, + "arm/cache-b15-rac:dying", + NULL, b15_rac_dying_cpu); + if (ret) + goto out_cpu_dead; +#endif + spin_lock(&rac_lock); reg = __raw_readl(b15_rac_base + RAC_CONFIG0_REG); for_each_possible_cpu(cpu) @@ -170,6 +255,12 @@ static int __init b15_rac_init(void) pr_info("Broadcom Brahma-B15 readahead cache at: 0x%p\n", b15_rac_base + RAC_CONFIG0_REG); + goto out; + +out_cpu_dead: + cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CACHE_B15_RAC_DYING); +out_unmap: + iounmap(b15_rac_base); out: of_node_put(dn); return ret; -- cgit v1.2.3