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 2017-12-01 01:10:11 +01:00 committed by Russell King
parent 1238c4fd48
commit 55de88778f
2 changed files with 93 additions and 0 deletions

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@ -13,6 +13,8 @@
#include <linux/io.h>
#include <linux/bitops.h>
#include <linux/of_address.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <asm/cacheflush.h>
#include <asm/hardware/cache-b15-rac.h>
@ -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;

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@ -59,6 +59,7 @@ enum cpuhp_state {
CPUHP_PCI_XGENE_DEAD,
CPUHP_IOMMU_INTEL_DEAD,
CPUHP_LUSTRE_CFS_DEAD,
CPUHP_AP_ARM_CACHE_B15_RAC_DEAD,
CPUHP_WORKQUEUE_PREP,
CPUHP_POWER_NUMA_PREPARE,
CPUHP_HRTIMERS_PREPARE,
@ -137,6 +138,7 @@ enum cpuhp_state {
CPUHP_AP_ARM64_ISNDEP_STARTING,
CPUHP_AP_SMPCFD_DYING,
CPUHP_AP_X86_TBOOT_DYING,
CPUHP_AP_ARM_CACHE_B15_RAC_DYING,
CPUHP_AP_ONLINE,
CPUHP_TEARDOWN_CPU,
CPUHP_AP_ONLINE_IDLE,