[PATCH v4 4/4] x86/of: Add support for boot time interrupt delivery mode configuration

[Rahul Tanwar]

Presently, init/boot time interrupt delivery mode is enumerated
only for ACPI enabled systems by parsing MADT table or for older
systems by parsing MP table. But for OF based x86 systems, it is
assumed & hardcoded to legacy PIC mode. This causes boot time crash
for platforms which do not use 8259 compliant legacy PIC.

Add support for configuration of init time interrupt delivery mode
for x86 OF based systems by introducing a new optional boolean
property 'intel,virtual-wire-mode' for interrupt-controller node
of local APIC. This property emulates IMCRP Bit 7 of MP feature
info byte 2 of MP floating pointer structure.

Defaults to legacy PIC mode if absent. Configures it to virtual
wire compatibility mode if present.

Signed-off-by: Rahul Tanwar <rtanwar@xxxxxxxxxxxxx>
---
 arch/x86/kernel/devicetree.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/devicetree.c b/arch/x86/kernel/devicetree.c
index fcc6f1b7818f..458e43490414 100644
--- a/arch/x86/kernel/devicetree.c
+++ b/arch/x86/kernel/devicetree.c
@@ -167,7 +167,14 @@ static void __init dtb_lapic_setup(void)
 			return;
 	}
 	smp_found_config = 1;
-	pic_mode = 1;
+	if (of_property_read_bool(dn, "intel,virtual-wire-mode")) {
+		pr_info("Virtual Wire compatibility mode.\n");
+		pic_mode = 0;
+	} else {
+		pr_info("IMCR and PIC compatibility mode.\n");
+		pic_mode = 1;
+	}
+
 	register_lapic_address(lapic_addr);
 }
 
-- 
2.17.1