Change in coreboot[master]: cpu/x86/lapic: Add comment on spurious interrupt

[Kyösti Mälkki (Code Review)]

Kyösti Mälkki has submitted this change. ( https://review.coreboot.org/c/coreboot/+/55699 )

Change subject: cpu/x86/lapic: Add comment on spurious interrupt
......................................................................

cpu/x86/lapic: Add comment on spurious interrupt

The bit LAPIC_SPIV_ENABLE returns 0 after reset even though
LAPIC has not been temporarily disabled.

Change-Id: Id261bc68fe9d1b1b0e5a3ef599a8f33a686d283b
Signed-off-by: Kyösti Mälkki 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55699
Tested-by: build bot (Jenkins) 
Reviewed-by: Angel Pons 
Reviewed-by: Nico Huber 
---
M src/cpu/x86/lapic/lapic.c
1 file changed, 3 insertions(+), 1 deletion(-)

Approvals:
  build bot (Jenkins): Verified
  Nico Huber: Looks good to me, approved
  Angel Pons: Looks good to me, approved

diff --git a/src/cpu/x86/lapic/lapic.c b/src/cpu/x86/lapic/lapic.c
index bd2fa67..a346bc1 100644
--- a/src/cpu/x86/lapic/lapic.c
+++ b/src/cpu/x86/lapic/lapic.c
@@ -47,9 +47,11 @@
     */
    lapic_update32(LAPIC_TASKPRI, ~LAPIC_TPRI_MASK, 0);

-	/* Put the local APIC in virtual wire mode */
+	/* Set spurious interrupt vector to 0 and keep LAPIC enabled to
+	   be able to clear LVT register mask bits. */
    lapic_update32(LAPIC_SPIV, ~LAPIC_VECTOR_MASK, LAPIC_SPIV_ENABLE);

+	/* Put the local APIC in virtual wire mode */
    uint32_t mask = LAPIC_LVT_MASKED | LAPIC_LVT_LEVEL_TRIGGER | LAPIC_LVT_REMOTE_IRR |
    		LAPIC_INPUT_POLARITY | LAPIC_SEND_PENDING | LAPIC_LVT_RESERVED_1 |
    		LAPIC_DELIVERY_MODE_MASK;