[PATCH 3/4] x86_64 io_apic: Implment update_irq0_entry

[Eric W. Biederman]

To guess different irq routing strategies for irq 0 we
need the ability to update our data structures to reflect
our guess.

update_irq0_entry updates the mp routing table information
to reflect our current guess as to the routing of the timer
irq.

Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
---
 arch/x86_64/kernel/io_apic.c |   31 +++++++++++++++++++++++++++++++
 1 files changed, 31 insertions(+), 0 deletions(-)

diff --git a/arch/x86_64/kernel/io_apic.c b/arch/x86_64/kernel/io_apic.c
index 5ad210f..1e68377 100644
--- a/arch/x86_64/kernel/io_apic.c
+++ b/arch/x86_64/kernel/io_apic.c
@@ -446,6 +446,37 @@ static int __init find_isa_irq_apic(int irq, int type)
 	return -1;
 }
 
+static int update_irq0_entry(int apic, int pin)
+{
+	int irq = 0;
+	int idx;
+	int isa_bus;
+
+	/* Figure out the isa bus, by convention it is bus 0,
+	 * but be prepared for someone being creative.
+	 */
+	for (isa_bus = 0; isa_bus < MAX_MP_BUSSES; isa_bus++)
+		if (test_bit(isa_bus, mp_bus_not_pci))
+			break;
+	if (isa_bus >= MAX_MP_BUSSES)
+		isa_bus = 0;
+
+	idx = find_irq_entry(apic, pin, mp_INT);
+	if (idx == -1) {
+		idx = mp_irq_entries;
+		if (++mp_irq_entries >= MAX_IRQ_SOURCES)
+			panic("MAX # of irq sources exceeded!!!\n");
+	}
+	mp_irqs[idx].mpc_type = MP_INTSRC;
+	mp_irqs[idx].mpc_irqtype = mp_INT;
+	mp_irqs[idx].mpc_irqflag = 0;	/* Use bus defaults */
+	mp_irqs[idx].mpc_srcbus = isa_bus;
+	mp_irqs[idx].mpc_srcbusirq = irq;
+	mp_irqs[idx].mpc_dstapic = mp_ioapics[apic].mpc_apicid;
+	mp_irqs[idx].mpc_dstirq = pin;
+	return idx;
+}
+
 /*
  * Find a specific PCI IRQ entry.
  * Not an __init, possibly needed by modules
-- 
1.4.4.1.g278f

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