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-rw-r--r--arch/powerpc/platforms/powernv/subcore.c392
1 files changed, 392 insertions, 0 deletions
diff --git a/arch/powerpc/platforms/powernv/subcore.c b/arch/powerpc/platforms/powernv/subcore.c
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+++ b/arch/powerpc/platforms/powernv/subcore.c
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+/*
+ * 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"
+
+
+/*
+ * 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);
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