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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 <alamyliu@broadcom.com> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Florian Fainelli
Russell King
parent
1238c4fd48
commit
55de88778f
@ -13,6 +13,8 @@
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#include <linux/io.h>
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#include <linux/bitops.h>
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#include <linux/of_address.h>
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#include <linux/notifier.h>
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#include <linux/cpu.h>
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#include <asm/cacheflush.h>
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#include <asm/hardware/cache-b15-rac.h>
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@ -42,6 +44,7 @@ extern void v7_flush_kern_cache_all(void);
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static void __iomem *b15_rac_base;
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static DEFINE_SPINLOCK(rac_lock);
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static u32 rac_config0_reg;
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/* Initialization flag to avoid checking for b15_rac_base, and to prevent
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* multi-platform kernels from crashing here as well.
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@ -137,6 +140,74 @@ static void b15_rac_enable(void)
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__b15_rac_enable(enable);
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}
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#ifdef CONFIG_HOTPLUG_CPU
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/* The CPU hotplug case is the most interesting one, we basically need to make
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* sure that the RAC is disabled for the entire system prior to having a CPU
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* die, in particular prior to this dying CPU having exited the coherency
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* domain.
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*
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* Once this CPU is marked dead, we can safely re-enable the RAC for the
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* remaining CPUs in the system which are still online.
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*
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* Offlining a CPU is the problematic case, onlining a CPU is not much of an
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* issue since the CPU and its cache-level hierarchy will start filling with
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* the RAC disabled, so L1 and L2 only.
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*
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* In this function, we should NOT have to verify any unsafe setting/condition
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* b15_rac_base:
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*
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* It is protected by the RAC_ENABLED flag which is cleared by default, and
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* being cleared when initial procedure is done. b15_rac_base had been set at
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* that time.
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*
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* RAC_ENABLED:
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* There is a small timing windows, in b15_rac_init(), between
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* cpuhp_setup_state_*()
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* ...
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* set RAC_ENABLED
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* However, there is no hotplug activity based on the Linux booting procedure.
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*
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* Since we have to disable RAC for all cores, we keep RAC on as long as as
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* possible (disable it as late as possible) to gain the cache benefit.
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*
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* Thus, dying/dead states are chosen here
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*
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* We are choosing not do disable the RAC on a per-CPU basis, here, if we did
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* we would want to consider disabling it as early as possible to benefit the
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* other active CPUs.
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*/
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/* Running on the dying CPU */
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static int b15_rac_dying_cpu(unsigned int cpu)
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{
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spin_lock(&rac_lock);
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/* Indicate that we are starting a hotplug procedure */
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__clear_bit(RAC_ENABLED, &b15_rac_flags);
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/* Disable the readahead cache and save its value to a global */
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rac_config0_reg = b15_rac_disable_and_flush();
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spin_unlock(&rac_lock);
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return 0;
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}
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/* Running on a non-dying CPU */
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static int b15_rac_dead_cpu(unsigned int cpu)
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{
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spin_lock(&rac_lock);
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/* And enable it */
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__b15_rac_enable(rac_config0_reg);
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__set_bit(RAC_ENABLED, &b15_rac_flags);
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spin_unlock(&rac_lock);
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return 0;
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}
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#endif /* CONFIG_HOTPLUG_CPU */
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static int __init b15_rac_init(void)
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{
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struct device_node *dn;
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@ -157,6 +228,20 @@ static int __init b15_rac_init(void)
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goto out;
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}
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#ifdef CONFIG_HOTPLUG_CPU
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ret = cpuhp_setup_state_nocalls(CPUHP_AP_ARM_CACHE_B15_RAC_DEAD,
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"arm/cache-b15-rac:dead",
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NULL, b15_rac_dead_cpu);
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if (ret)
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goto out_unmap;
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ret = cpuhp_setup_state_nocalls(CPUHP_AP_ARM_CACHE_B15_RAC_DYING,
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"arm/cache-b15-rac:dying",
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NULL, b15_rac_dying_cpu);
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if (ret)
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goto out_cpu_dead;
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#endif
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spin_lock(&rac_lock);
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reg = __raw_readl(b15_rac_base + RAC_CONFIG0_REG);
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for_each_possible_cpu(cpu)
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@ -170,6 +255,12 @@ static int __init b15_rac_init(void)
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pr_info("Broadcom Brahma-B15 readahead cache at: 0x%p\n",
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b15_rac_base + RAC_CONFIG0_REG);
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goto out;
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out_cpu_dead:
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cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CACHE_B15_RAC_DYING);
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out_unmap:
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iounmap(b15_rac_base);
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out:
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of_node_put(dn);
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return ret;
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@ -59,6 +59,7 @@ enum cpuhp_state {
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CPUHP_PCI_XGENE_DEAD,
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CPUHP_IOMMU_INTEL_DEAD,
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CPUHP_LUSTRE_CFS_DEAD,
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CPUHP_AP_ARM_CACHE_B15_RAC_DEAD,
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CPUHP_WORKQUEUE_PREP,
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CPUHP_POWER_NUMA_PREPARE,
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CPUHP_HRTIMERS_PREPARE,
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@ -137,6 +138,7 @@ enum cpuhp_state {
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CPUHP_AP_ARM64_ISNDEP_STARTING,
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CPUHP_AP_SMPCFD_DYING,
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CPUHP_AP_X86_TBOOT_DYING,
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CPUHP_AP_ARM_CACHE_B15_RAC_DYING,
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CPUHP_AP_ONLINE,
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CPUHP_TEARDOWN_CPU,
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CPUHP_AP_ONLINE_IDLE,
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