Re: [PATCH V15 11/12] MIPS: Loongson 3: Add CPU hotplug support

[Aurelien Jarno <aurelien@aurel32.net>]

On Sun, Dec 15, 2013 at 08:14:35PM +0800, Huacai Chen wrote:
> Tips of Loongson's CPU hotplug:
> 1, To fully shutdown a core in Loongson 3, the target core should go to
>    CKSEG1 and flush all L1 cache entries at first. Then, another core
>    (usually Core 0) can safely disable the clock of the target core. So
>    play_dead() call loongson3_play_dead() via CKSEG1 (both uncached and
>    unmmaped).
> 2, The default clocksource of Loongson is MIPS. Since clock source is a
>    global device, timekeeping need the CP0' Count registers of each core
>    be synchronous. Thus, when a core is up, we use a SMP_ASK_C0COUNT IPI
>    to ask Core-0's Count.
> 
> Signed-off-by: Huacai Chen <chenhc@lemote.com>
> Signed-off-by: Hongliang Tao <taohl@lemote.com>
> Signed-off-by: Hua Yan <yanh@lemote.com>
> ---
>  arch/mips/Kconfig                              |    1 +
>  arch/mips/include/asm/mach-loongson/loongson.h |    6 +-
>  arch/mips/include/asm/smp.h                    |    1 +
>  arch/mips/loongson/loongson-3/irq.c            |   10 ++
>  arch/mips/loongson/loongson-3/smp.c            |  168 +++++++++++++++++++++++-
>  5 files changed, 181 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 2c447a7..ef5fa84 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -276,6 +276,7 @@ config LASAT
>  config MACH_LOONGSON
>  	bool "Loongson family of machines"
>  	select SYS_SUPPORTS_ZBOOT
> +	select SYS_SUPPORTS_HOTPLUG_CPU
>  	help
>  	  This enables the support of Loongson family of machines.
>  
> diff --git a/arch/mips/include/asm/mach-loongson/loongson.h b/arch/mips/include/asm/mach-loongson/loongson.h
> index 40b4892..d4bae71 100644
> --- a/arch/mips/include/asm/mach-loongson/loongson.h
> +++ b/arch/mips/include/asm/mach-loongson/loongson.h
> @@ -247,6 +247,9 @@ static inline void do_perfcnt_IRQ(void)
>  #define LOONGSON_PXARB_CFG		LOONGSON_REG(LOONGSON_REGBASE + 0x68)
>  #define LOONGSON_PXARB_STATUS		LOONGSON_REG(LOONGSON_REGBASE + 0x6c)
>  
> +/* Chip Config */
> +#define LOONGSON_CHIPCFG0		LOONGSON_REG(LOONGSON_REGBASE + 0x80)

LOONGSON_REG uses LOONGSON_REG_BASE, which seems to be Loongson-2
specific. Here, LOONGSON3_REG should probably be used instead.

> +
>  /* pcimap */
>  
>  #define LOONGSON_PCIMAP_PCIMAP_LO0	0x0000003f
> @@ -262,9 +265,6 @@ static inline void do_perfcnt_IRQ(void)
>  #ifdef CONFIG_CPU_SUPPORTS_CPUFREQ
>  #include <linux/cpufreq.h>
>  extern struct cpufreq_frequency_table loongson2_clockmod_table[];
> -
> -/* Chip Config */
> -#define LOONGSON_CHIPCFG0		LOONGSON_REG(LOONGSON_REGBASE + 0x80)
>  #endif
>  
>  /*
> diff --git a/arch/mips/include/asm/smp.h b/arch/mips/include/asm/smp.h
> index eb60087..efa02ac 100644
> --- a/arch/mips/include/asm/smp.h
> +++ b/arch/mips/include/asm/smp.h
> @@ -42,6 +42,7 @@ extern int __cpu_logical_map[NR_CPUS];
>  #define SMP_ICACHE_FLUSH	0x4
>  /* Used by kexec crashdump to save all cpu's state */
>  #define SMP_DUMP		0x8
> +#define SMP_ASK_C0COUNT		0x10
>  
>  extern volatile cpumask_t cpu_callin_map;
>  
> diff --git a/arch/mips/loongson/loongson-3/irq.c b/arch/mips/loongson/loongson-3/irq.c
> index 11467ca..16e88a9 100644
> --- a/arch/mips/loongson/loongson-3/irq.c
> +++ b/arch/mips/loongson/loongson-3/irq.c
> @@ -125,3 +125,13 @@ void __init mach_init_irq(void)
>  
>  	set_c0_status(STATUSF_IP2 | STATUSF_IP6);
>  }
> +
> +#ifdef CONFIG_HOTPLUG_CPU
> +
> +void fixup_irqs(void)
> +{
> +	irq_cpu_offline();
> +	clear_c0_status(ST0_IM);
> +}
> +
> +#endif
> diff --git a/arch/mips/loongson/loongson-3/smp.c b/arch/mips/loongson/loongson-3/smp.c
> index 3c52565..8cc5e95 100644
> --- a/arch/mips/loongson/loongson-3/smp.c
> +++ b/arch/mips/loongson/loongson-3/smp.c
> @@ -30,6 +30,9 @@
>  
>  #include "smp.h"
>  
> +DEFINE_PER_CPU(int, cpu_state);
> +DEFINE_PER_CPU(uint32_t, core0_c0count);
> +
>  /* read a 64bit value from ipi register */
>  uint64_t loongson3_ipi_read64(void * addr)
>  {
> @@ -169,8 +172,8 @@ static void loongson3_send_ipi_mask(const struct cpumask *mask, unsigned int act
>  
>  void loongson3_ipi_interrupt(struct pt_regs *regs)
>  {
> -	int cpu = smp_processor_id();
> -	unsigned int action;
> +	int i, cpu = smp_processor_id();
> +	unsigned int action, c0count;
>  
>  	/* Load the ipi register to figure out what we're supposed to do */
>  	action = loongson3_ipi_read32(ipi_status0_regs[cpu]);
> @@ -185,14 +188,24 @@ void loongson3_ipi_interrupt(struct pt_regs *regs)
>  	if (action & SMP_CALL_FUNCTION) {
>  		smp_call_function_interrupt();
>  	}
> +
> +	if (action & SMP_ASK_C0COUNT) {
> +		BUG_ON(cpu != 0);
> +		c0count = read_c0_count();
> +		for (i=1; i < nr_cpus_loongson; i++)
> +			per_cpu(core0_c0count, i) = c0count;
> +	}
>  }
>  
> +#define MAX_LOOPS 1000
>  /*
>   * SMP init and finish on secondary CPUs
>   */
>  void loongson3_init_secondary(void)
>  {
>  	int i;
> +	uint32_t initcount;
> +	unsigned int cpu = smp_processor_id();
>  	unsigned int imask = STATUSF_IP7 | STATUSF_IP6 |
>  			     STATUSF_IP3 | STATUSF_IP2;
>  
> @@ -202,6 +215,19 @@ void loongson3_init_secondary(void)
>  	for (i = 0; i < nr_cpus_loongson; i++) {
>  		loongson3_ipi_write32(0xffffffff, ipi_en0_regs[i]);
>  	}
> +
> +	per_cpu(cpu_state, cpu) = CPU_ONLINE;
> +
> +	i = 0;
> +	__get_cpu_var(core0_c0count) = 0;
> +	loongson3_send_ipi_single(0, SMP_ASK_C0COUNT);
> +	while (!__get_cpu_var(core0_c0count))
> +		i++;
> +
> +	if (i > MAX_LOOPS)
> +		i = MAX_LOOPS;
> +	initcount = __get_cpu_var(core0_c0count) + i;
> +	write_c0_count(initcount);
>  }
>  
>  void loongson3_smp_finish(void)
> @@ -235,6 +261,8 @@ void __init loongson3_smp_setup(void)
>  
>  void __init loongson3_prepare_cpus(unsigned int max_cpus)
>  {
> +	init_cpu_present(cpu_possible_mask);
> +	per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
>  }
>  
>  /*
> @@ -268,6 +296,138 @@ void __init loongson3_cpus_done(void)
>  {
>  }
>  
> +#ifdef CONFIG_HOTPLUG_CPU
> +
> +extern void fixup_irqs(void);
> +extern void (*flush_cache_all)(void);
> +
> +static int loongson3_cpu_disable(void)
> +{
> +	unsigned long flags;
> +	unsigned int cpu = smp_processor_id();
> +
> +	if (cpu == 0)
> +		return -EBUSY;
> +
> +	set_cpu_online(cpu, false);
> +	cpu_clear(cpu, cpu_callin_map);
> +	local_irq_save(flags);
> +	fixup_irqs();
> +	local_irq_restore(flags);
> +	flush_cache_all();
> +	local_flush_tlb_all();
> +
> +	return 0;
> +}
> +
> +
> +static void loongson3_cpu_die(unsigned int cpu)
> +{
> +	while (per_cpu(cpu_state, cpu) != CPU_DEAD)
> +		cpu_relax();
> +
> +	mb();
> +}
> +
> +/* To shutdown a core in Loongson 3, the target core should go to CKSEG1 and
> + * flush all L1 entries at first. Then, another core (usually Core 0) can
> + * safely disable the clock of the target core. loongson3_play_dead() is
> + * called via CKSEG1 (uncached and unmmaped) */
> +void loongson3_play_dead(int *state_addr)
> +{
> +	__asm__ __volatile__(
> +		"      .set push                         \n"
> +		"      .set noreorder                    \n"
> +		"      li $t0, 0x80000000                \n" /* KSEG0 */
> +		"      li $t1, 512                       \n" /* num of L1 entries */

Patch 2 parses the configuration of the caches, shouldn't it be better
to use values from there instead of hardcoded entry. Also 


> +		"1:    cache 0, 0($t0)                   \n" /* flush L1 ICache */
> +		"      cache 0, 1($t0)                   \n"
> +		"      cache 0, 2($t0)                   \n"
> +		"      cache 0, 3($t0)                   \n"
> +		"      cache 1, 0($t0)                   \n" /* flush L1 DCache */
> +		"      cache 1, 1($t0)                   \n"
> +		"      cache 1, 2($t0)                   \n"
> +		"      cache 1, 3($t0)                   \n"
> +		"      addiu $t0, $t0, 0x20              \n"
> +		"      bnez  $t1, 1b                     \n"
> +		"      addiu $t1, $t1, -1                \n"
> +		"      li    $t0, 0x7                    \n" /* *state_addr = CPU_DEAD; */
> +		"      sw    $t0, 0($a0)                 \n"
> +		"      sync                              \n"
> +		"      cache 21, 0($a0)                  \n" /* flush entry of *state_addr */
> +		"      .set pop                          \n");
> +
> +	__asm__ __volatile__(
> +		"      .set push                         \n"
> +		"      .set noreorder                    \n"
> +		"      .set mips64                       \n"

This seems to say again that a 32-bit kernel is not possible and that
32-bit kernel should be dropped, and this removed.

> +		"      mfc0  $t2, $15, 1                 \n"
> +		"      andi  $t2, 0x3ff                  \n"
> +		"      dli   $t0, 0x900000003ff01000     \n"
> +		"      andi  $t3, $t2, 0x3               \n"
> +		"      sll   $t3, 8                      \n"  /* get cpu id */
> +		"      or    $t0, $t0, $t3               \n"
> +		"      andi  $t1, $t2, 0xc               \n"
> +		"      dsll  $t1, 42                     \n"  /* get node id */
> +		"      or    $t0, $t0, $t1               \n"
> +		"1:    li    $a0, 0x100                  \n"  /* wait for init loop */
> +		"2:    bnez  $a0, 2b                     \n"  /* idle loop */
> +		"      addiu $a0, -1                     \n"

How this idle loop has been calibrated? Why is it needed?

> +		"      lw    $v0, 0x20($t0)              \n"  /* get PC via mailbox */
> +		"      beqz  $v0, 1b                     \n"
> +		"      nop                               \n"
> +		"      ld    $sp, 0x28($t0)              \n"  /* get SP via mailbox */
> +		"      ld    $gp, 0x30($t0)              \n"  /* get GP via mailbox */
> +		"      ld    $a1, 0x38($t0)              \n"
> +		"      jr  $v0                           \n"  /* jump to initial PC */
> +		"      nop                               \n"
> +		"      .set pop                          \n");
> +}
> +
> +void play_dead(void)
> +{
> +	int *state_addr;
> +	unsigned int cpu = smp_processor_id();
> +	void (*play_dead_at_ckseg1)(int *);
> +
> +	idle_task_exit();
> +	play_dead_at_ckseg1 = (void *)CKSEG1ADDR((unsigned long)loongson3_play_dead);
> +	state_addr = &per_cpu(cpu_state, cpu);
> +	mb();
> +	play_dead_at_ckseg1(state_addr);
> +}
> +
> +#define CPU_POST_DEAD_FROZEN	(CPU_POST_DEAD | CPU_TASKS_FROZEN)
> +static int loongson3_cpu_callback(struct notifier_block *nfb,
> +	unsigned long action, void *hcpu)
> +{
> +	unsigned int cpu = (unsigned long)hcpu;
> +
> +	switch (action) {
> +	case CPU_POST_DEAD:
> +	case CPU_POST_DEAD_FROZEN:
> +		printk(KERN_INFO "Disable clock for CPU#%d\n", cpu);
> +		LOONGSON_CHIPCFG0 &= ~(1 << (12 + cpu));
> +		break;
> +	case CPU_UP_PREPARE:
> +	case CPU_UP_PREPARE_FROZEN:
> +		printk(KERN_INFO "Enable clock for CPU#%d\n", cpu);
> +		LOONGSON_CHIPCFG0 |= 1 << (12 + cpu);
> +		break;
> +	}
> +
> +	return NOTIFY_OK;
> +}
> +
> +static int register_loongson3_notifier(void)
> +{
> +	hotcpu_notifier(loongson3_cpu_callback, 0);
> +	return 0;
> +}
> +early_initcall(register_loongson3_notifier);
> +
> +#endif
> +
>  struct plat_smp_ops loongson3_smp_ops = {
>  	.send_ipi_single = loongson3_send_ipi_single,
>  	.send_ipi_mask = loongson3_send_ipi_mask,
> @@ -277,4 +437,8 @@ struct plat_smp_ops loongson3_smp_ops = {
>  	.boot_secondary = loongson3_boot_secondary,
>  	.smp_setup = loongson3_smp_setup,
>  	.prepare_cpus = loongson3_prepare_cpus,
> +#ifdef CONFIG_HOTPLUG_CPU
> +	.cpu_disable = loongson3_cpu_disable,
> +	.cpu_die = loongson3_cpu_die,
> +#endif
>  };

This patch should also modify Kconfig to add SYS_SUPPORTS_HOTPLUG_CPU to
the LEMOTE_MACH3A machine.

-- 
Aurelien Jarno	                        GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net