/*
* Copyright 2013, Michael (Ellerman|Neuling), IBM Corporation.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#define pr_fmt(fmt) "powernv: " fmt
#include <linux/kernel.h>
#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <linux/device.h>
#include <linux/gfp.h>
#include <linux/smp.h>
#include <linux/stop_machine.h>
#include <asm/cputhreads.h>
#include <asm/kvm_ppc.h>
#include <asm/machdep.h>
#include <asm/opal.h>
#include <asm/smp.h>
#include "subcore.h"
#include "powernv.h"
/*
* Split/unsplit procedure:
*
* A core can be in one of three states, unsplit, 2-way split, and 4-way split.
*
* The mapping to subcores_per_core is simple:
*
* State | subcores_per_core
* ------------|------------------
* Unsplit | 1
* 2-way split | 2
* 4-way split | 4
*
* The core is split along thread boundaries, the mapping between subcores and
* threads is as follows:
*
* Unsplit:
* ----------------------------
* Subcore | 0 |
* ----------------------------
* Thread | 0 1 2 3 4 5 6 7 |
* ----------------------------
*
* 2-way split:
* -------------------------------------
* Subcore | 0 | 1 |
* -------------------------------------
* Thread | 0 1 2 3 | 4 5 6 7 |
* -------------------------------------
*
* 4-way split:
* -----------------------------------------
* Subcore | 0 | 1 | 2 | 3 |
* -----------------------------------------
* Thread | 0 1 | 2 3 | 4 5 | 6 7 |
* -----------------------------------------
*
*
* Transitions
* -----------
*
* It is not possible to transition between either of the split states, the
* core must first be unsplit. The legal transitions are:
*
* ----------- ---------------
* | | <----> | 2-way split |
* | | ---------------
* | Unsplit |
* | | ---------------
* | | <----> | 4-way split |
* ----------- ---------------
*
* Unsplitting
* -----------
*
* Unsplitting is the simpler procedure. It requires thread 0 to request the
* unsplit while all other threads NAP.
*
* Thread 0 clears HID0_POWER8_DYNLPARDIS (Dynamic LPAR Disable). This tells
* the hardware that if all threads except 0 are napping, the hardware should
* unsplit the core.
*
* Non-zero threads are sent to a NAP loop, they don't exit the loop until they
* see the core unsplit.
*
* Core 0 spins waiting for the hardware to see all the other threads napping
* and perform the unsplit.
*
* Once thread 0 sees the unsplit, it IPIs the secondary threads to wake them
* out of NAP. They will then see the core unsplit and exit the NAP loop.
*
* Splitting
* ---------
*
* The basic splitting procedure is fairly straight forward. However it is
* complicated by the fact that after the split occurs, the newly created
* subcores are not in a fully initialised state.
*
* Most notably the subcores do not have the correct value for SDR1, which
* means they must not be running in virtual mode when the split occurs. The
* subcores have separate timebases SPRs but these are pre-synchronised by
* opal.
*
* To begin with secondary threads are sent to an assembly routine. There they
* switch to real mode, so they are immune to the uninitialised SDR1 value.
* Once in real mode they indicate that they are in real mode, and spin waiting
* to see the core split.
*
* Thread 0 waits to see that all secondaries are in real mode, and then begins
* the splitting procedure. It firstly sets HID0_POWER8_DYNLPARDIS, which
* prevents the hardware from unsplitting. Then it sets the appropriate HID bit
* to request the split, and spins waiting to see that the split has happened.
*
* Concurrently the secondaries will notice the split. When they do they set up
* their SPRs, notably SDR1, and then they can return to virtual mode and exit
* the procedure.
*/
/* Initialised at boot by subcore_init() */
static int subcores_per_core;
/*
* Used to communicate to offline cpus that we want them to pop out of the
* offline loop and do a split or unsplit.
*
* 0 - no split happening
* 1 - unsplit in progress
* 2 - split to 2 in progress
* 4 - split to 4 in progress
*/
static int new_split_mode;
static cpumask_var_t cpu_offline_mask;
struct split_state {
u8 step;
u8 master;
};
static DEFINE_PER_CPU(struct split_state, split_state);
static void wait_for_sync_step(int step)
{
int i, cpu = smp_processor_id();
for (i = cpu + 1; i < cpu + threads_per_core; i++)
while(per_cpu(split_state, i).step < step)
barrier();
/* Order the wait loop vs any subsequent loads/stores. */
mb();
}
static void unsplit_core(void)
{
u64 hid0, mask;
int i, cpu;
mask = HID0_POWER8_2LPARMODE | HID0_POWER8_4LPARMODE;
cpu = smp_processor_id();
if (cpu_thread_in_core(cpu) != 0) {
while (mfspr(SPRN_HID0) & mask)
power7_nap(0);
per_cpu(split_state, cpu).step = SYNC_STEP_UNSPLIT;
return;
}
hid0 = mfspr(SPRN_HID0);
hid0 &= ~HID0_POWER8_DYNLPARDIS;
mtspr(SPRN_HID0, hid0);
while (mfspr(SPRN_HID0) & mask)
cpu_relax();
/* Wake secondaries out of NAP */
for (i = cpu + 1; i < cpu + threads_per_core; i++)
smp_send_reschedule(i);
wait_for_sync_step(SYNC_STEP_UNSPLIT);
}
static void split_core(int new_mode)
{
struct { u64 value; u64 mask; } split_parms[2] = {
{ HID0_POWER8_1TO2LPAR, HID0_POWER8_2LPARMODE },
{ HID0_POWER8_1TO4LPAR, HID0_POWER8_4LPARMODE }
};
int i, cpu;
u64 hid0;
/* Convert new_mode (2 or 4) into an index into our parms array */
i = (new_mode >> 1) - 1;
BUG_ON(i < 0 || i > 1);
cpu = smp_processor_id();
if (cpu_thread_in_core(cpu) != 0) {
split_core_secondary_loop(&per_cpu(split_state, cpu).step);
return;
}
wait_for_sync_step(SYNC_STEP_REAL_MODE);
/* Write new mode */
hid0 = mfspr(SPRN_HID0);
hid0 |= HID0_POWER8_DYNLPARDIS | split_parms[i].value;
mtspr(SPRN_HID0, hid0);
/* Wait for it to happen */
while (!(mfspr(SPRN_HID0) & split_parms[i].mask))
cpu_relax();
}
static void cpu_do_split(int new_mode)
{
/*
* At boot subcores_per_core will be 0, so we will always unsplit at
* boot. In the usual case where the core is already unsplit it's a
* nop, and this just ensures the kernel's notion of the mode is
* consistent with the hardware.
*/
if (subcores_per_core != 1)
unsplit_core();
if (new_mode != 1)
split_core(new_mode);
mb();
per_cpu(split_state, smp_processor_id()).step = SYNC_STEP_FINISHED;
}
bool cpu_core_split_required(void)
{
smp_rmb();
if (!new_split_mode)
return false;
cpu_do_split(new_split_mode);
return true;
}
static int cpu_update_split_mode(void *data)
{
int cpu, new_mode = *(int *)data;
if (this_cpu_ptr(&split_state)->master) {
new_split_mode = new_mode;
smp_wmb();
cpumask_andnot(cpu_offline_mask, cpu_present_mask,
cpu_online_mask);
/* This should work even though the cpu is offline */
for_each_cpu(cpu, cpu_offline_mask)
smp_send_reschedule(cpu);
}
cpu_do_split(new_mode);
if (this_cpu_ptr(&split_state)->master) {
/* Wait for all cpus to finish before we touch subcores_per_core */
for_each_present_cpu(cpu) {
if (cpu >= setup_max_cpus)
break;
while(per_cpu(split_state, cpu).step < SYNC_STEP_FINISHED)
barrier();
}
new_split_mode = 0;
/* Make the new mode public */
subcores_per_core = new_mode;
threads_per_subcore = threads_per_core / subcores_per_core;
/* Make sure the new mode is written before we exit */
mb();
}
return 0;
}
static int set_subcores_per_core(int new_mode)
{
struct split_state *state;
int cpu;
if (kvm_hv_mode_active()) {
pr_err("Unable to change split core mode while KVM active.\n");
return -EBUSY;
}
/*
* We are only called at boot, or from the sysfs write. If that ever
* changes we'll need a lock here.
*/
BUG_ON(new_mode < 1 || new_mode > 4 || new_mode == 3);
for_each_present_cpu(cpu) {
state = &per_cpu(split_state, cpu);
state->step = SYNC_STEP_INITIAL;
state->master = 0;
}
get_online_cpus();
/* This cpu will update the globals before exiting stop machine */
this_cpu_ptr(&split_state)->master = 1;
/* Ensure state is consistent before we call the other cpus */
mb();
stop_machine(cpu_update_split_mode, &new_mode, cpu_online_mask);
put_online_cpus();
return 0;
}
static ssize_t __used store_subcores_per_core(struct device *dev,
struct device_attribute *attr, const char *buf,
size_t count)
{
unsigned long val;
int rc;
/* We are serialised by the attribute lock */
rc = sscanf(buf, "%lx", &val);
if (rc != 1)
return -EINVAL;
switch (val) {
case 1:
case 2:
case 4:
if (subcores_per_core == val)
/* Nothing to do */
goto out;
break;
default:
return -EINVAL;
}
rc = set_subcores_per_core(val);
if (rc)
return rc;
out:
return count;
}
static ssize_t show_subcores_per_core(struct device *dev,
struct device_attribute *attr, char *buf)
{
return sprintf(buf, "%x\n", subcores_per_core);
}
static DEVICE_ATTR(subcores_per_core, 0644,
show_subcores_per_core, store_subcores_per_core);
static int subcore_init(void)
{
if (!cpu_has_feature(CPU_FTR_ARCH_207S))
return 0;
/*
* We need all threads in a core to be present to split/unsplit so
* continue only if max_cpus are aligned to threads_per_core.
*/
if (setup_max_cpus % threads_per_core)
return 0;
BUG_ON(!alloc_cpumask_var(&cpu_offline_mask, GFP_KERNEL));
set_subcores_per_core(1);
return device_create_file(cpu_subsys.dev_root,
&dev_attr_subcores_per_core);
}
machine_device_initcall(powernv, subcore_init);