[PATCH v3 4/4] x86/of: Add support for boot time interrupt delivery mode configuration

[Rahul Tanwar <rtanwar@maxlinear.com>]

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 is a bug for
platforms which are OF based but do not use 8259 compliant legacy
PIC interrupt controller. Such platforms can not even boot because
of this bug/hardcoding.

Fix this bug by adding 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.

Fixes: 3879a6f32948 ("x86: dtb: Add early parsing of IO_APIC")
Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rahul Tanwar <rtanwar@maxlinear.com>
---
 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