[MIPS] IRQ Affinity Support for SMTC on Malta Platform
Signed-off-by: Kevin D. Kissell <kevink@mips.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 3b807b4..b09eee2 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -1378,6 +1378,19 @@
impact on interrupt service overhead. Disable it only if you know
what you are doing.
+config MIPS_MT_SMTC_IRQAFF
+ bool "Support IRQ affinity API"
+ depends on MIPS_MT_SMTC
+ default n
+ help
+ Enables SMP IRQ affinity API (/proc/irq/*/smp_affinity, etc.)
+ for SMTC Linux kernel. Requires platform support, of which
+ an example can be found in the MIPS kernel i8259 and Malta
+ platform code. It is recommended that MIPS_MT_SMTC_INSTANT_REPLAY
+ be enabled if MIPS_MT_SMTC_IRQAFF is used. Adds overhead to
+ interrupt dispatch, and should be used only if you know what
+ you are doing.
+
config MIPS_VPE_LOADER_TOM
bool "Load VPE program into memory hidden from linux"
depends on MIPS_VPE_LOADER
diff --git a/arch/mips/kernel/i8259.c b/arch/mips/kernel/i8259.c
index 3a2d255..4f4359b 100644
--- a/arch/mips/kernel/i8259.c
+++ b/arch/mips/kernel/i8259.c
@@ -39,6 +39,9 @@
.disable = disable_8259A_irq,
.unmask = enable_8259A_irq,
.mask_ack = mask_and_ack_8259A,
+#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
+ .set_affinity = plat_set_irq_affinity,
+#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */
};
/*
diff --git a/arch/mips/kernel/smtc.c b/arch/mips/kernel/smtc.c
index f094043..fe22387 100644
--- a/arch/mips/kernel/smtc.c
+++ b/arch/mips/kernel/smtc.c
@@ -606,6 +606,60 @@
return setup_irq(irq, new);
}
+#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
+/*
+ * Support for IRQ affinity to TCs
+ */
+
+void smtc_set_irq_affinity(unsigned int irq, cpumask_t affinity)
+{
+ /*
+ * If a "fast path" cache of quickly decodable affinity state
+ * is maintained, this is where it gets done, on a call up
+ * from the platform affinity code.
+ */
+}
+
+void smtc_forward_irq(unsigned int irq)
+{
+ int target;
+
+ /*
+ * OK wise guy, now figure out how to get the IRQ
+ * to be serviced on an authorized "CPU".
+ *
+ * Ideally, to handle the situation where an IRQ has multiple
+ * eligible CPUS, we would maintain state per IRQ that would
+ * allow a fair distribution of service requests. Since the
+ * expected use model is any-or-only-one, for simplicity
+ * and efficiency, we just pick the easiest one to find.
+ */
+
+ target = first_cpu(irq_desc[irq].affinity);
+
+ /*
+ * We depend on the platform code to have correctly processed
+ * IRQ affinity change requests to ensure that the IRQ affinity
+ * mask has been purged of bits corresponding to nonexistent and
+ * offline "CPUs", and to TCs bound to VPEs other than the VPE
+ * connected to the physical interrupt input for the interrupt
+ * in question. Otherwise we have a nasty problem with interrupt
+ * mask management. This is best handled in non-performance-critical
+ * platform IRQ affinity setting code, to minimize interrupt-time
+ * checks.
+ */
+
+ /* If no one is eligible, service locally */
+ if (target >= NR_CPUS) {
+ do_IRQ_no_affinity(irq);
+ return;
+ }
+
+ smtc_send_ipi(target, IRQ_AFFINITY_IPI, irq);
+}
+
+#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */
+
/*
* IPI model for SMTC is tricky, because interrupts aren't TC-specific.
* Within a VPE one TC can interrupt another by different approaches.
@@ -830,6 +884,15 @@
break;
}
break;
+#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
+ case IRQ_AFFINITY_IPI:
+ /*
+ * Accept a "forwarded" interrupt that was initially
+ * taken by a TC who doesn't have affinity for the IRQ.
+ */
+ do_IRQ_no_affinity((int)arg_copy);
+ break;
+#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */
default:
printk("Impossible SMTC IPI Type 0x%x\n", type_copy);
break;
diff --git a/arch/mips/mips-boards/malta/malta_smtc.c b/arch/mips/mips-boards/malta/malta_smtc.c
index ae05d05..5c980f4 100644
--- a/arch/mips/mips-boards/malta/malta_smtc.c
+++ b/arch/mips/mips-boards/malta/malta_smtc.c
@@ -88,3 +88,53 @@
void prom_cpus_done(void)
{
}
+
+#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
+/*
+ * IRQ affinity hook
+ */
+
+
+void plat_set_irq_affinity(unsigned int irq, cpumask_t affinity)
+{
+ cpumask_t tmask = affinity;
+ int cpu = 0;
+ void smtc_set_irq_affinity(unsigned int irq, cpumask_t aff);
+
+ /*
+ * On the legacy Malta development board, all I/O interrupts
+ * are routed through the 8259 and combined in a single signal
+ * to the CPU daughterboard, and on the CoreFPGA2/3 34K models,
+ * that signal is brought to IP2 of both VPEs. To avoid racing
+ * concurrent interrupt service events, IP2 is enabled only on
+ * one VPE, by convention VPE0. So long as no bits are ever
+ * cleared in the affinity mask, there will never be any
+ * interrupt forwarding. But as soon as a program or operator
+ * sets affinity for one of the related IRQs, we need to make
+ * sure that we don't ever try to forward across the VPE boundry,
+ * at least not until we engineer a system where the interrupt
+ * _ack() or _end() function can somehow know that it corresponds
+ * to an interrupt taken on another VPE, and perform the appropriate
+ * restoration of Status.IM state using MFTR/MTTR instead of the
+ * normal local behavior. We also ensure that no attempt will
+ * be made to forward to an offline "CPU".
+ */
+
+ for_each_cpu_mask(cpu, affinity) {
+ if ((cpu_data[cpu].vpe_id != 0) || !cpu_online(cpu))
+ cpu_clear(cpu, tmask);
+ }
+ irq_desc[irq].affinity = tmask;
+
+ if (cpus_empty(tmask))
+ /*
+ * We could restore a default mask here, but the
+ * runtime code can anyway deal with the null set
+ */
+ printk(KERN_WARNING
+ "IRQ affinity leaves no legal CPU for IRQ %d\n", irq);
+
+ /* Do any generic SMTC IRQ affinity setup */
+ smtc_set_irq_affinity(irq, tmask);
+}
+#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */
diff --git a/include/asm-mips/irq.h b/include/asm-mips/irq.h
index 2cb52cf..a58f0ee 100644
--- a/include/asm-mips/irq.h
+++ b/include/asm-mips/irq.h
@@ -46,6 +46,38 @@
#endif /* CONFIG_MIPS_MT_SMTC */
+#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
+#include <linux/cpumask.h>
+
+extern void plat_set_irq_affinity(unsigned int irq, cpumask_t affinity);
+extern void smtc_forward_irq(unsigned int irq);
+
+/*
+ * IRQ affinity hook invoked at the beginning of interrupt dispatch
+ * if option is enabled.
+ *
+ * Up through Linux 2.6.22 (at least) cpumask operations are very
+ * inefficient on MIPS. Initial prototypes of SMTC IRQ affinity
+ * used a "fast path" per-IRQ-descriptor cache of affinity information
+ * to reduce latency. As there is a project afoot to optimize the
+ * cpumask implementations, this version is optimistically assuming
+ * that cpumask.h macro overhead is reasonable during interrupt dispatch.
+ */
+#define IRQ_AFFINITY_HOOK(irq) \
+do { \
+ if (!cpu_isset(smp_processor_id(), irq_desc[irq].affinity)) { \
+ smtc_forward_irq(irq); \
+ irq_exit(); \
+ return; \
+ } \
+} while (0)
+
+#else /* Not doing SMTC affinity */
+
+#define IRQ_AFFINITY_HOOK(irq) do { } while (0)
+
+#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */
+
#ifdef CONFIG_MIPS_MT_SMTC_IM_BACKSTOP
/*
@@ -56,13 +88,27 @@
*/
#define __DO_IRQ_SMTC_HOOK(irq) \
do { \
+ IRQ_AFFINITY_HOOK(irq); \
if (irq_hwmask[irq] & 0x0000ff00) \
write_c0_tccontext(read_c0_tccontext() & \
- ~(irq_hwmask[irq] & 0x0000ff00)); \
+ ~(irq_hwmask[irq] & 0x0000ff00)); \
} while (0)
+
+#define __NO_AFFINITY_IRQ_SMTC_HOOK(irq) \
+do { \
+ if (irq_hwmask[irq] & 0x0000ff00) \
+ write_c0_tccontext(read_c0_tccontext() & \
+ ~(irq_hwmask[irq] & 0x0000ff00)); \
+} while (0)
+
#else
-#define __DO_IRQ_SMTC_HOOK(irq) do { } while (0)
+#define __DO_IRQ_SMTC_HOOK(irq) \
+do { \
+ IRQ_AFFINITY_HOOK(irq); \
+} while (0)
+#define __NO_AFFINITY_IRQ_SMTC_HOOK(irq) do { } while (0)
+
#endif
/*
@@ -81,6 +127,23 @@
irq_exit(); \
} while (0)
+#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
+/*
+ * To avoid inefficient and in some cases pathological re-checking of
+ * IRQ affinity, we have this variant that skips the affinity check.
+ */
+
+
+#define do_IRQ_no_affinity(irq) \
+do { \
+ irq_enter(); \
+ __NO_AFFINITY_IRQ_SMTC_HOOK(irq); \
+ generic_handle_irq(irq); \
+ irq_exit(); \
+} while (0)
+
+#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */
+
extern void arch_init_irq(void);
extern void spurious_interrupt(void);
diff --git a/include/asm-mips/smtc_ipi.h b/include/asm-mips/smtc_ipi.h
index a52a4a7..e09131a 100644
--- a/include/asm-mips/smtc_ipi.h
+++ b/include/asm-mips/smtc_ipi.h
@@ -34,6 +34,7 @@
#define LINUX_SMP_IPI 1
#define SMTC_CLOCK_TICK 2
+#define IRQ_AFFINITY_IPI 3
/*
* A queue of IPI messages