From 4683d674b67f973a2d42b4a398db251c5f79dae6 Mon Sep 17 00:00:00 2001
From: SarahW <pcem@pcem-emulator.co.uk>
Date: Mon, 9 Nov 2020 19:29:21 +0000
Subject: [PATCH] Implement PIIX SMI gate. Fixes some issues seen on Shuttle
 HOT-433 when power management disabled in BIOS, which results in the BIOS
 failing to initialise and relocate the SMI handler but still advertise APM
 availability.

---
 src/piix.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/piix.c b/src/piix.c
index 35eebe2..4e76b26 100644
--- a/src/piix.c
+++ b/src/piix.c
@@ -29,9 +29,11 @@ static sff_busmaster_t piix_busmaster[2];
 static uint8_t piix_rc = 0;
 static void (*piix_nb_reset)();
 
+#define REG_SMICNTL 0xa0
 #define REG_SMIEN 0xa2
 #define REG_SMIREQ 0xaa
 
+#define SMICNTL_CSMIGATE (1 << 0)
 #define SMIEN_APMC   (1 << 7)
 #define SMIREQ_RAPMC (1 << 7)
 
@@ -262,7 +264,8 @@ static void piix_apm_write(uint16_t port, uint8_t val, void *p)
                 {
                         card_piix[REG_SMIREQ] |= SMIREQ_RAPMC;
 //                        pclog("APMC write causes SMI\n");
-                        x86_smi_trigger();
+                        if (card_piix[REG_SMICNTL] & SMICNTL_CSMIGATE)
+                                x86_smi_trigger();
                 }
                 break;