3705ff6da5
There is a subtle race in the CPU hotplug code, where a CPU which has been offlined can online itself before being requested, which results in things going astray on the next online/offline cycle. What happens in the normal online/offline/online cycle is: CPU0 CPU3 requests boot of CPU3 pen_release = 3 flush cache line checks pen_release, reads 3 starts boot pen_release = -1 ... requests CPU3 offline ... ... dies ... checks pen_release, reads -1 requests boot of CPU3 pen_release = 3 flush cache line checks pen_release, reads 3 starts boot pen_release = -1 However, as the write of -1 of pen_release is not fully flushed back to memory, and the checking of pen_release is done with caches disabled, this allows CPU3 the opportunity to read the old value of pen_release: CPU0 CPU3 requests boot of CPU3 pen_release = 3 flush cache line checks pen_release, reads 3 starts boot pen_release = -1 ... requests CPU3 offline ... ... dies ... checks pen_release, reads 3 starts boot pen_release = -1 requests boot of CPU3 pen_release = 3 flush cache line Fix this by grouping the write of pen_release along with its cache line flushing code to ensure that any update to pen_release is always pushed out to physical memory. Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
160 lines
3.9 KiB
C
160 lines
3.9 KiB
C
/*
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* Copyright (C) 2002 ARM Ltd.
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* Copyright (C) 2008 STMicroelctronics.
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* Copyright (C) 2009 ST-Ericsson.
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* Author: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
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*
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* This file is based on arm realview platform
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/init.h>
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#include <linux/errno.h>
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#include <linux/delay.h>
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#include <linux/device.h>
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#include <linux/smp.h>
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#include <linux/io.h>
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#include <asm/cacheflush.h>
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#include <asm/smp_scu.h>
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#include <mach/hardware.h>
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/*
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* control for which core is the next to come out of the secondary
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* boot "holding pen"
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*/
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volatile int __cpuinitdata pen_release = -1;
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/*
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* Write pen_release in a way that is guaranteed to be visible to all
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* observers, irrespective of whether they're taking part in coherency
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* or not. This is necessary for the hotplug code to work reliably.
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*/
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static void write_pen_release(int val)
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{
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pen_release = val;
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smp_wmb();
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__cpuc_flush_dcache_area((void *)&pen_release, sizeof(pen_release));
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outer_clean_range(__pa(&pen_release), __pa(&pen_release + 1));
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}
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static DEFINE_SPINLOCK(boot_lock);
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void __cpuinit platform_secondary_init(unsigned int cpu)
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{
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/*
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* if any interrupts are already enabled for the primary
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* core (e.g. timer irq), then they will not have been enabled
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* for us: do so
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*/
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gic_cpu_init(0, __io_address(UX500_GIC_CPU_BASE));
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/*
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* let the primary processor know we're out of the
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* pen, then head off into the C entry point
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*/
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write_pen_release(-1);
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/*
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* Synchronise with the boot thread.
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*/
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spin_lock(&boot_lock);
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spin_unlock(&boot_lock);
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}
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int __cpuinit boot_secondary(unsigned int cpu, struct task_struct *idle)
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{
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unsigned long timeout;
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/*
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* set synchronisation state between this boot processor
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* and the secondary one
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*/
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spin_lock(&boot_lock);
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/*
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* The secondary processor is waiting to be released from
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* the holding pen - release it, then wait for it to flag
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* that it has been released by resetting pen_release.
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*/
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write_pen_release(cpu);
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smp_cross_call(cpumask_of(cpu), 1);
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timeout = jiffies + (1 * HZ);
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while (time_before(jiffies, timeout)) {
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if (pen_release == -1)
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break;
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}
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/*
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* now the secondary core is starting up let it run its
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* calibrations, then wait for it to finish
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*/
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spin_unlock(&boot_lock);
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return pen_release != -1 ? -ENOSYS : 0;
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}
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static void __init wakeup_secondary(void)
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{
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/*
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* write the address of secondary startup into the backup ram register
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* at offset 0x1FF4, then write the magic number 0xA1FEED01 to the
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* backup ram register at offset 0x1FF0, which is what boot rom code
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* is waiting for. This would wake up the secondary core from WFE
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*/
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#define U8500_CPU1_JUMPADDR_OFFSET 0x1FF4
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__raw_writel(virt_to_phys(u8500_secondary_startup),
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__io_address(UX500_BACKUPRAM0_BASE) +
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U8500_CPU1_JUMPADDR_OFFSET);
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#define U8500_CPU1_WAKEMAGIC_OFFSET 0x1FF0
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__raw_writel(0xA1FEED01,
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__io_address(UX500_BACKUPRAM0_BASE) +
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U8500_CPU1_WAKEMAGIC_OFFSET);
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/* make sure write buffer is drained */
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mb();
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}
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/*
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* Initialise the CPU possible map early - this describes the CPUs
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* which may be present or become present in the system.
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*/
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void __init smp_init_cpus(void)
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{
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unsigned int i, ncores;
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ncores = scu_get_core_count(__io_address(UX500_SCU_BASE));
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/* sanity check */
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if (ncores > NR_CPUS) {
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printk(KERN_WARNING
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"U8500: no. of cores (%d) greater than configured "
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"maximum of %d - clipping\n",
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ncores, NR_CPUS);
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ncores = NR_CPUS;
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}
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for (i = 0; i < ncores; i++)
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set_cpu_possible(i, true);
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}
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void __init platform_smp_prepare_cpus(unsigned int max_cpus)
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{
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int i;
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/*
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* Initialise the present map, which describes the set of CPUs
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* actually populated at the present time.
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*/
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for (i = 0; i < max_cpus; i++)
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set_cpu_present(i, true);
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scu_enable(__io_address(UX500_SCU_BASE));
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wakeup_secondary();
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}
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