Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 55de8877 authored by Florian Fainelli's avatar Florian Fainelli Committed by Russell King
Browse files

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: default avatarAlamy Liu <alamyliu@broadcom.com>
Signed-off-by: default avatarFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: default avatarRussell King <rmk+kernel@armlinux.org.uk>
parent 1238c4fd

arch/arm/mm/cache-b15-rac.c

+91 −0
Original line number Original line Diff line number Diff line
@@ -13,6 +13,8 @@ 
#include <linux/io.h>

#include <linux/io.h>

#include <linux/bitops.h>

#include <linux/bitops.h>

#include <linux/of_address.h>

#include <linux/of_address.h>

#include <linux/notifier.h>

#include <linux/cpu.h>





#include <asm/cacheflush.h>

#include <asm/cacheflush.h>

#include <asm/hardware/cache-b15-rac.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 void __iomem *b15_rac_base;

static DEFINE_SPINLOCK(rac_lock);

static DEFINE_SPINLOCK(rac_lock);

static u32 rac_config0_reg;





/* Initialization flag to avoid checking for b15_rac_base, and to prevent

/* Initialization flag to avoid checking for b15_rac_base, and to prevent

 * multi-platform kernels from crashing here as well.

 * multi-platform kernels from crashing here as well.
@@ -137,6 +140,74 @@ static void b15_rac_enable(void) 
	__b15_rac_enable(enable);

	__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)

static int __init b15_rac_init(void)

{

{

	struct device_node *dn;

	struct device_node *dn;
@@ -157,6 +228,20 @@ static int __init b15_rac_init(void) 
		goto out;

		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);

	spin_lock(&rac_lock);

	reg = __raw_readl(b15_rac_base + RAC_CONFIG0_REG);

	reg = __raw_readl(b15_rac_base + RAC_CONFIG0_REG);

	for_each_possible_cpu(cpu)

	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",

	pr_info("Broadcom Brahma-B15 readahead cache at: 0x%p\n",

		b15_rac_base + RAC_CONFIG0_REG);

		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:

out:

	of_node_put(dn);

	of_node_put(dn);

	return ret;

	return ret;

include/linux/cpuhotplug.h

+2 −0
Original line number Original line Diff line number Diff line
@@ -59,6 +59,7 @@ enum cpuhp_state { 
	CPUHP_PCI_XGENE_DEAD,

	CPUHP_PCI_XGENE_DEAD,

	CPUHP_IOMMU_INTEL_DEAD,

	CPUHP_IOMMU_INTEL_DEAD,

	CPUHP_LUSTRE_CFS_DEAD,

	CPUHP_LUSTRE_CFS_DEAD,

	CPUHP_AP_ARM_CACHE_B15_RAC_DEAD,

	CPUHP_WORKQUEUE_PREP,

	CPUHP_WORKQUEUE_PREP,

	CPUHP_POWER_NUMA_PREPARE,

	CPUHP_POWER_NUMA_PREPARE,

	CPUHP_HRTIMERS_PREPARE,

	CPUHP_HRTIMERS_PREPARE,
@@ -137,6 +138,7 @@ enum cpuhp_state { 
	CPUHP_AP_ARM64_ISNDEP_STARTING,

	CPUHP_AP_ARM64_ISNDEP_STARTING,

	CPUHP_AP_SMPCFD_DYING,

	CPUHP_AP_SMPCFD_DYING,

	CPUHP_AP_X86_TBOOT_DYING,

	CPUHP_AP_X86_TBOOT_DYING,

	CPUHP_AP_ARM_CACHE_B15_RAC_DYING,

	CPUHP_AP_ONLINE,

	CPUHP_AP_ONLINE,

	CPUHP_TEARDOWN_CPU,

	CPUHP_TEARDOWN_CPU,

	CPUHP_AP_ONLINE_IDLE,

	CPUHP_AP_ONLINE_IDLE,