From 1fc9b4b56e8425f5f68c019b511189f25c82c122 Mon Sep 17 00:00:00 2001
From: Samuel Thibault <samuel.thibault@ens-lyon.org>
Date: Mon, 11 Nov 2019 17:37:12 +0100
Subject: PIC: Acknowledge interrupts more carefully

Specs seems to be saying that we should mask an irq out while
acknowledging it with EOI. Also, better acknowledge only the concerned
irq.

* i386/i386at/interrupt.S (interrupt): Mask irq before notifying EOI.
Using specific EOI instead of unspecific EOI.
---
 i386/i386at/interrupt.S | 44 +++++++++++++++++++++++++++++++++++++-------
 1 file changed, 37 insertions(+), 7 deletions(-)

diff --git a/i386/i386at/interrupt.S b/i386/i386at/interrupt.S
index 076e34bc..23a2e582 100644
--- a/i386/i386at/interrupt.S
+++ b/i386/i386at/interrupt.S
@@ -38,14 +38,44 @@ ENTRY(interrupt)
 	addl	$4,%esp			/* pop unit number */
 	call	splx_cli		/* restore previous ipl */
 	addl	$4,%esp			/* pop previous ipl */
+
 	cli				/* XXX no more nested interrupts */
-	popl	%eax			/* restore irq number */
-	movl	%eax,%ecx		/* copy irq number */
-	movb	$(NON_SPEC_EOI),%al	/* non-specific EOI */
-	outb	%al,$(PIC_MASTER_ICW)	/* ack interrupt to master */
+	popl	%ecx			/* restore irq number */
+
+	movl	$1,%eax
+	shll	%cl,%eax		/* get corresponding IRQ mask */
+	orl	EXT(curr_pic_mask),%eax /* add current mask */
+
 	cmpl	$8,%ecx			/* do we need to ack slave? */
-	jl	1f			/* no, skip it */
-	outb	%al,$(PIC_SLAVE_ICW)
+	jl	1f			/* no, only master */
+
+	/* EOI on slave */
+	movb	%ah,%al
+	outb	%al,$(PIC_SLAVE_OCW)	/* mask slave out */
+
+	movb	$(SPECIFIC_EOI),%al	/* specific EOI for this irq */
+	andb	$7,%cl			/* irq number for the slave */
+	orb	%cl,%al			/* combine them */
+	outb	%al,$(PIC_SLAVE_ICW)	/* ack interrupt to slave */
+
+	movb	$(SPECIFIC_EOI + I_AM_SLAVE_2),%al	/* specific master EOI for cascaded slave */
+	outb	%al,$(PIC_MASTER_ICW)	/* ack interrupt to master */
+
+	movl	EXT(curr_pic_mask),%eax /* restore original mask */
+	movb	%ah,%al
+	outb	%al,$(PIC_SLAVE_OCW)	/* unmask slave */
+	jmp	2f
+
 1:
-	ret				/* return */
+	/* EOI on master */
+	outb	%al,$(PIC_MASTER_OCW)	/* mask master out */
+
+	movb	$(SPECIFIC_EOI),%al	/* specific EOI for this irq */
+	orb	%cl,%al			/* combine with irq number */
+	outb	%al,$(PIC_MASTER_ICW)	/* ack interrupt to master */
+
+	movl	EXT(curr_pic_mask),%eax /* restore original mask */
+	outb	%al,$(PIC_MASTER_OCW)	/* unmask master */
+2:
+	ret
 END(interrupt)
-- 
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