[PATCH 02/12] powermac: support G5 CPU hotplug

Johannes Berg
2007-02-12T15:15:54Z

This patch allows "hotplugging" of CPUs on G5 machines. CPUs that are
disabled are put into an idle loop with the decrementer frequency set
to minimum. To wake them up again we kick them just like when bringing
them up.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>

---
This one seems better. I just soft-disable interrupts from the idle
function and exit it to reset the decrementer.

arch/powerpc/kernel/idle_power4.S | 14 +++++++++----
arch/powerpc/platforms/powermac/setup.c | 34 +++++++++++++++++++++++++++++++-
arch/powerpc/platforms/powermac/smp.c | 12 +++++++++--
include/asm-powerpc/machdep.h | 2 +
4 files changed, 55 insertions(+), 7 deletions(-)

--- linux-2.6-git.orig/arch/powerpc/platforms/powermac/smp.c 2007-02-12 15:35:52.380522210 +0100
+++ linux-2.6-git/arch/powerpc/platforms/powermac/smp.c 2007-02-12 15:36:12.990522210 +0100
@@ -897,7 +897,7 @@ void smp_core99_cpu_die(unsigned int cpu
cpu_dead[cpu] = 0;
}

-#endif
+#endif /* CONFIG_HOTPLUG_CPU && CONFIG_PP32 */

/* Core99 Macs (dual G4s and G5s) */
struct smp_ops_t core99_smp_ops = {
@@ -907,8 +907,16 @@ struct smp_ops_t core99_smp_ops = {
.setup_cpu = smp_core99_setup_cpu,
.give_timebase = smp_core99_give_timebase,
.take_timebase = smp_core99_take_timebase,
-#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PPC32)
+#if defined(CONFIG_HOTPLUG_CPU)
+# if defined(CONFIG_PPC32)
.cpu_disable = smp_core99_cpu_disable,
.cpu_die = smp_core99_cpu_die,
+# endif
+# if defined(CONFIG_PPC64)
+ .cpu_disable = generic_cpu_disable,
+ .cpu_die = generic_cpu_die,
+ /* intentionally do *NOT* assign cpu_enable,
+ * the generic code will use kick_cpu then! */
+# endif
#endif
};
--- linux-2.6-git.orig/arch/powerpc/platforms/powermac/setup.c 2007-02-12 15:35:52.418522210 +0100
+++ linux-2.6-git/arch/powerpc/platforms/powermac/setup.c 2007-02-12 15:39:42.512522210 +0100
@@ -425,6 +425,9 @@ static int initializing = 1;
static int pmac_late_init(void)
{
initializing = 0;
+ /* this is udbg (which is __init) and we can later use it during
+ * cpu hotplug (in smp_core99_kick_cpu) */
+ ppc_md.progress = NULL;
return 0;
}

@@ -651,6 +654,35 @@ static int pmac_pci_probe_mode(struct pc
return PCI_PROBE_NORMAL;
return PCI_PROBE_DEVTREE;
}
+
+#ifdef CONFIG_HOTPLUG_CPU
+/* access per cpu vars from generic smp.c */
+DECLARE_PER_CPU(int, cpu_state);
+
+static void pmac_cpu_die(void)
+{
+ /* turn off as much as possible, we'll be
+ * kicked out as this will only be invoked
+ * on core99 platforms for now ... */
+
+ printk(KERN_INFO "CPU#%d offline\n", smp_processor_id());
+ __get_cpu_var(cpu_state) = CPU_DEAD;
+ smp_wmb();
+
+ /* during the path that leads here preemption is disabled,
+ * reenable it now so that when coming up preempt count is
+ * zero correctly */
+ preempt_enable();
+
+ while (1) {
+ /* let's not take timer interrupts too often ... */
+ set_dec(0x7fffffff);
+
+ power4_idle_irqs_softdisabled();
+ }
+}
+#endif
+
#endif

define_machine(powermac) {
@@ -689,6 +721,6 @@ define_machine(powermac) {
.phys_mem_access_prot = pci_phys_mem_access_prot,
#endif
#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PPC64)
- .cpu_die = generic_mach_cpu_die,
+ .cpu_die = pmac_cpu_die,
#endif
};
--- linux-2.6-git.orig/arch/powerpc/kernel/idle_power4.S 2007-02-12 15:35:52.493522210 +0100
+++ linux-2.6-git/arch/powerpc/kernel/idle_power4.S 2007-02-12 15:39:20.382522210 +0100
@@ -19,7 +19,12 @@

.text

+_GLOBAL(power4_idle_irqs_softdisabled)
+ li r6,1
+ b 0f
_GLOBAL(power4_idle)
+ li r6,0
+0:
BEGIN_FTR_SECTION
blr
END_FTR_SECTION_IFCLR(CPU_FTR_CAN_NAP)
@@ -35,8 +40,8 @@ END_FTR_SECTION_IFCLR(CPU_FTR_CAN_NAP)
rotldi r0,r0,16
mtmsrd r0,1 /* hard-disable interrupts */
li r0,1
- stb r0,PACASOFTIRQEN(r13) /* we'll hard-enable shortly */
- stb r0,PACAHARDIRQEN(r13)
+ stb r0,PACAHARDIRQEN(r13) /* we'll hard-enable shortly */
+ stb r6,PACASOFTIRQEN(r13) /* set softirqs enabled bit */
BEGIN_FTR_SECTION
DSSALL
sync
@@ -51,5 +56,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
isync
mtmsrd r7
isync
- b 1b
-
+ beq- 1b /* cr0 is still set, exit if this
+ is power4_idle_irqs_softdisabled */
+ blr
--- linux-2.6-git.orig/include/asm-powerpc/machdep.h 2007-02-12 15:35:52.551522210 +0100
+++ linux-2.6-git/include/asm-powerpc/machdep.h 2007-02-12 15:36:13.006522210 +0100
@@ -252,6 +252,8 @@ struct machdep_calls {

extern void power4_idle(void);
extern void ppc6xx_idle(void);
+/* this one is for CPU hotplug (e.g. powermac) */
+extern void power4_idle_irqs_softdisabled(void);

/*
* ppc_md contains a copy of the machine description structure for the