[PATCH 2/7] powerpc/85xx: add HOTPLUG_CPU support

[Li Yang-R58472]

>Subject: Re: [PATCH 2/7] powerpc/85xx: add HOTPLUG_CPU support
>
>On 11/04/2011 07:31 AM, Zhao Chenhui wrote:
>> From: Li Yang <leoli at freescale.com>
>>
>> Add support to disable and re-enable individual cores at runtime
>> on MPC85xx/QorIQ SMP machines. Currently support e500 core.
>>
>> MPC85xx machines use ePAPR spin-table in boot page for CPU kick-off.
>> This patch uses the boot page from bootloader to boot core at runtime.
>> It supports 32-bit and 36-bit physical address.
>
>Note that there is no guarantee that the bootloader can handle you
>resetting a core.  In ePAPR the spin table is a one-time release
>mechanism, not a core reset mechanism.  If this has a U-Boot dependency,
>document that.

Actually we suggested to add a spin table in kernel so that we won't have the dependency on u-boot.  But there seems to be some opposite opinion in the internal discussion.  I personally prefer to remove the u-boot dependency and add the mechanism in kernel.

>
>>  #ifdef CONFIG_SMP
>>  /* When we get here, r24 needs to hold the CPU # */
>>  	.globl __secondary_start
>> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
>> index 7bf2187..12a54f0 100644
>> --- a/arch/powerpc/kernel/smp.c
>> +++ b/arch/powerpc/kernel/smp.c
>> @@ -381,8 +381,14 @@ void generic_cpu_die(unsigned int cpu)
>>
>>  	for (i = 0; i < 100; i++) {
>>  		smp_rmb();
>> -		if (per_cpu(cpu_state, cpu) == CPU_DEAD)
>> +		if (per_cpu(cpu_state, cpu) == CPU_DEAD) {
>> +			/*
>> +			 * After another core sets cpu_state to CPU_DEAD,
>> +			 * it needs some time to die.
>> +			 */
>> +			msleep(10);
>>  			return;
>> +		}
>>  		msleep(100);
>
>It would be better to do this as a call into platform-specific code than
>can check registers to determine whether the core has checked out (in
>our case, whether it has entered nap) -- or to do a suitable delay for
>that platform if this isn't possible.

It will be easier if we can add a platform specific cpu_die instead of using the generic one?

>
>> diff --git a/arch/powerpc/platforms/85xx/smp.c
>b/arch/powerpc/platforms/85xx/smp.c
>> index 9b0de9c..5a54fc1 100644
>> --- a/arch/powerpc/platforms/85xx/smp.c
>> +++ b/arch/powerpc/platforms/85xx/smp.c
>> @@ -17,6 +17,7 @@
>>  #include <linux/of.h>
>>  #include <linux/kexec.h>
>>  #include <linux/highmem.h>
>> +#include <linux/cpu.h>
>>
>>  #include <asm/machdep.h>
>>  #include <asm/pgtable.h>
>> @@ -30,26 +31,141 @@
>>
>>  extern void __early_start(void);
>>
>> -#define BOOT_ENTRY_ADDR_UPPER	0
>> -#define BOOT_ENTRY_ADDR_LOWER	1
>> -#define BOOT_ENTRY_R3_UPPER	2
>> -#define BOOT_ENTRY_R3_LOWER	3
>> -#define BOOT_ENTRY_RESV		4
>> -#define BOOT_ENTRY_PIR		5
>> -#define BOOT_ENTRY_R6_UPPER	6
>> -#define BOOT_ENTRY_R6_LOWER	7
>> -#define NUM_BOOT_ENTRY		8
>> -#define SIZE_BOOT_ENTRY		(NUM_BOOT_ENTRY * sizeof(u32))
>> -
>> -static int __init
>> -smp_85xx_kick_cpu(int nr)
>> +#define MPC85xx_BPTR_OFF		0x00020
>> +#define MPC85xx_BPTR_EN			0x80000000
>> +#define MPC85xx_BPTR_BOOT_PAGE_MASK	0x00ffffff
>> +#define MPC85xx_BRR_OFF			0xe0e4
>> +#define MPC85xx_ECM_EEBPCR_OFF		0x01010
>> +#define MPC85xx_PIC_PIR_OFF		0x41090
>> +
>> +struct epapr_entry {
>
>ePAPR is more than just the spin table.  Call it something like
>epapr_spin_table.
>
>> +	u32	addr_h;
>> +	u32	addr_l;
>> +	u32	r3_h;
>> +	u32	r3_l;
>> +	u32	reserved;
>> +	u32	pir;
>> +	u32	r6_h;
>> +	u32	r6_l;
>> +};
>
>Get rid of r6, it is not part of the ePAPR spin table.

Agree.

>
>> +static int is_corenet;
>> +static void __cpuinit smp_85xx_setup_cpu(int cpu_nr);
>> +
>> +#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PPC32)
>
>Why PPC32?

Not sure if it is the same for e5500.  E5500 support will be verified later.

>
>> +extern void flush_disable_L1(void);
>
>If this isn't already in a header file, put it in one.
>
>> +static void __cpuinit smp_85xx_mach_cpu_die(void)
>> +{
>> +	unsigned int cpu = smp_processor_id();
>> +	register u32 tmp;
>> +
>> +	local_irq_disable();
>> +	idle_task_exit();
>> +	generic_set_cpu_dead(cpu);
>> +	smp_wmb();
>> +
>> +	mtspr(SPRN_TSR, TSR_ENW | TSR_WIS | TSR_DIS | TSR_FIS);
>> +	mtspr(SPRN_TCR, 0);
>
>If clearing TSR matters at all (I'm not sure that it does), first clear
>TCR, then TSR.
>
>> +	flush_disable_L1();
>
>You'll also need to take down L2 on e500mc.

Right.  E500mc support is beyond this patch series.  We will work on it after the e500v2 support is finalized.

>
>> +	tmp = 0;
>> +	if (cpu_has_feature(CPU_FTR_CAN_NAP))
>> +		tmp = HID0_NAP;
>> +	else if (cpu_has_feature(CPU_FTR_CAN_DOZE))
>> +		tmp = HID0_DOZE;
>
>Those FTR bits are for what we can do in idle, and can be cleared if the
>user sets CONFIG_BDI_SWITCH.

It is powersave_nap variable shows what we can do in idle.  I think it's correct to use the CPU_FTR_CAN_* macro as CPU capability.

>
>On 85xx we always want to nap here, and at least on e500mc it seems to
>be mandatory.  From the p5020 RM description of PIR:
>
>> For proper system operation, a core should be reset in this way only if
>the core is already in nap or sleep
>> state. Because a core in either state cannot perform the necessary write
>to cause a hard reset, a core cannot
>> put itself into hard reset.
>
>Note that on e500mc we don't use HID0/MSR_WE to enter nap, we need to
>hit the CCSR register.  And unless you can somehow guarantee that only
>one core at a time is doing this, we'll need some oher core to actually
>place us in nap (since once we enter nap we're not running so can't
>release a lock).
>
>> +	if (tmp) {
>> +		tmp |= mfspr(SPRN_HID0) & ~(HID0_DOZE|HID0_NAP|HID0_SLEEP);
>> +
>> +		smp_mb();
>
>smp_mb()?  This is always SMP...  It looks like you meant some specific
>sync instruction as part of an architected sequence, so just use that.
>
>> +		isync();
>> +		mtspr(SPRN_HID0, tmp);
>> +		isync();
>> +
>> +		tmp = mfmsr();
>> +		tmp |= MSR_WE;
>> +		smp_mb();
>> +		mtmsr(tmp);
>> +		isync();
>> +	}
>> +
>> +	for (;;);
>> +}
>> +
>> +static void __cpuinit smp_85xx_reset_core(int nr)
>> +{
>> +	__iomem u32 *vaddr, *pir_vaddr;
>> +	u32 val, cpu_mask;
>> +
>> +	/* If CoreNet platform, use BRR as release register. */
>> +	if (is_corenet) {
>> +		cpu_mask = 1 << nr;
>> +		vaddr = ioremap(get_immrbase() + MPC85xx_BRR_OFF, 4);
>> +	} else {
>> +		cpu_mask = 1 << (24 + nr);
>> +		vaddr = ioremap(get_immrbase() + MPC85xx_ECM_EEBPCR_OFF, 4);
>> +	}
>
>Please use the device tree node, not get_immrbase().

The get_immrbase() implementation uses the device tree node.

>
>> +	val = in_be32(vaddr);
>> +	if (!(val & cpu_mask)) {
>> +		out_be32(vaddr, val | cpu_mask);
>> +	} else {
>> +		/* reset core */
>> +		pir_vaddr = ioremap(get_immrbase() + MPC85xx_PIC_PIR_OFF, 4);
>> +		val = in_be32(pir_vaddr);
>> +		/* reset assert */
>> +		val |= (1 << nr);
>> +		out_be32(pir_vaddr, val);
>
>Use setbits32().
>
>> +		val = in_be32(pir_vaddr);
>> +		val &= ~(1 << nr);
>> +		/* reset negate */
>> +		out_be32(pir_vaddr, val);
>
>clrbits32().
>
>Is there any amount of time we need to keep the reset pin asserted?

We don't know, but it's already working without any wait.

>
>> +		iounmap(pir_vaddr);
>> +	}
>> +	iounmap(vaddr);
>> +}
>> +
>> +static int __cpuinit smp_85xx_map_bootpg(u32 page)
>> +{
>> +	__iomem u32 *bootpg_ptr;
>> +	u32 bptr;
>> +
>> +	/* Get the BPTR */
>> +	bootpg_ptr = ioremap(get_immrbase() + MPC85xx_BPTR_OFF, 4);
>> +
>> +	/* Set the BPTR to the secondary boot page */
>> +	bptr = MPC85xx_BPTR_EN | (page & MPC85xx_BPTR_BOOT_PAGE_MASK);
>> +	out_be32(bootpg_ptr, bptr);
>> +
>> +	iounmap(bootpg_ptr);
>> +	return 0;
>> +}
>
>Shouldn't the boot page already be set by U-Boot?

The register should be lost after a deep sleep.   Better to do it again.

>
>> +static int __cpuinit smp_85xx_kick_cpu(int nr)
>>  {
>>  	unsigned long flags;
>>  	const u64 *cpu_rel_addr;
>> -	__iomem u32 *bptr_vaddr;
>> +	__iomem struct epapr_entry *epapr;
>>  	struct device_node *np;
>> -	int n = 0;
>> +	int n = 0, hw_cpu = get_hard_smp_processor_id(nr);
>>  	int ioremappable;
>> +	int ret = 0;
>>
>>  	WARN_ON (nr < 0 || nr >= NR_CPUS);
>>
>> @@ -73,46 +189,79 @@ smp_85xx_kick_cpu(int nr)
>>
>>  	/* Map the spin table */
>>  	if (ioremappable)
>> -		bptr_vaddr = ioremap(*cpu_rel_addr, SIZE_BOOT_ENTRY);
>> +		epapr = ioremap(*cpu_rel_addr, sizeof(struct epapr_entry));
>>  	else
>> -		bptr_vaddr = phys_to_virt(*cpu_rel_addr);
>> +		epapr = phys_to_virt(*cpu_rel_addr);
>>
>>  	local_irq_save(flags);
>>
>> -	out_be32(bptr_vaddr + BOOT_ENTRY_PIR, nr);
>> +	out_be32(&epapr->pir, hw_cpu);
>>  #ifdef CONFIG_PPC32
>> -	out_be32(bptr_vaddr + BOOT_ENTRY_ADDR_LOWER, __pa(__early_start));
>> +#ifdef CONFIG_HOTPLUG_CPU
>> +	if (system_state == SYSTEM_RUNNING) {
>> +		out_be32(&epapr->addr_l, 0);
>> +		smp_85xx_map_bootpg((u32)(*cpu_rel_addr >> PAGE_SHIFT));
>
>Why is this inside PPC32?

Not tested on 64-bit yet.  Might require a different implementation on PPC64.

>
>> +		smp_85xx_reset_core(hw_cpu);
>> +
>> +		/* wait until core is ready... */
>> +		n = 0;
>> +		while ((in_be32(&epapr->addr_l) != 1) && (++n < 1000))
>> +			udelay(100);
>> +		if (n > 1000) {
>
>if (n == 1000)
>
>or
>
>if (in_be32(&epapr->addr_l) != 1)
>
>> +			pr_err("timeout waiting for core%d to reset\n",	nr);
>> +			ret = -ENOENT;
>> +			goto out;
>> +		}
>> +		/*  clear the acknowledge status */
>> +		__secondary_hold_acknowledge = -1;
>> +
>> +		smp_85xx_unmap_bootpg();
>> +	}
>> +#endif
>> +	out_be32(&epapr->addr_l, __pa(__early_start));
>>
>>  	if (!ioremappable)
>> -		flush_dcache_range((ulong)bptr_vaddr,
>> -				(ulong)(bptr_vaddr + SIZE_BOOT_ENTRY));
>> +		flush_dcache_range((ulong)epapr,
>> +				(ulong)epapr + sizeof(struct epapr_entry));
>>
>>  	/* Wait a bit for the CPU to ack. */
>> -	while ((__secondary_hold_acknowledge != nr) && (++n < 1000))
>> +	n = 0;
>> +	while ((__secondary_hold_acknowledge != hw_cpu) && (++n < 1000))
>>  		mdelay(1);
>> +	if (n > 1000) {
>
>if (n == 1000)
>
>or
>
>if (__secondary_hold_acknowledge != hw_cpu)
>
>> +		pr_err("timeout waiting for core%d to ack\n", nr);
>
>pr_err("%s: timeout waiting for core %d to ack\n", __func__, nr);
>
>Likewise elsewhere.  Maybe also/instead mention hw_cpu.
>
>> +		ret = -ENOENT;
>> +		goto out;
>> +	}
>> +out:
>>  #else
>>  	smp_generic_kick_cpu(nr);
>>
>> -	out_be64((u64 *)(bptr_vaddr + BOOT_ENTRY_ADDR_UPPER),
>> +	out_be64((u64 *)(&epapr->addr_h),
>>  		__pa((u64)*((unsigned long long *)
>generic_secondary_smp_init)));
>>
>>  	if (!ioremappable)
>> -		flush_dcache_range((ulong)bptr_vaddr,
>> -				(ulong)(bptr_vaddr + SIZE_BOOT_ENTRY));
>> +		flush_dcache_range((ulong)epapr,
>> +				(ulong)epapr + sizeof(struct epapr_entry));
>
>We don't wait for the core to come up on 64-bit?

Not sure about it.  But at least the normal boot up should be tested on P5020, right?

>
>> @@ -228,14 +376,18 @@ void __init mpc85xx_smp_init(void)
>>  {
>>  	struct device_node *np;
>>
>> -	smp_85xx_ops.setup_cpu = smp_85xx_setup_cpu;
>> -
>>  	np = of_find_node_by_type(NULL, "open-pic");
>>  	if (np) {
>>  		smp_85xx_ops.probe = smp_mpic_probe;
>>  		smp_85xx_ops.message_pass = smp_mpic_message_pass;
>>  	}
>>
>> +	/* Check if the chip is based on CoreNet platform. */
>> +	is_corenet = 0;
>> +	np = of_find_compatible_node(NULL, NULL, "fsl,qoriq-device-config-
>1.0");
>> +	if (np)
>> +		is_corenet = 1;
>
>Please also check for the non-corenet guts node.  If you don't find
>either, disable the mechanism -- you're probably running under a
>hypervisor.

Ok.

- Leo