From 07ca753124f9d15f6c27373e0db1c787d7765937 Mon Sep 17 00:00:00 2001
From: Conrad Pankoff <deoxxa@fknsrs.biz>
Date: Sat, 28 Sep 2019 21:52:56 +1000
Subject: [PATCH] Kernel: Fix BIOS date/time on hardware

It turns out some BIOS vendors don't support non-BCD date/time mode, but
we were relying on it being available. We no longer do this, but instead
check whether the BIOS claims to provide BCD or regular binary values for
its date/time data.
---
 Kernel/RTC.cpp | 37 +++++++++++++++++++++++++++----------
 1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/Kernel/RTC.cpp b/Kernel/RTC.cpp
index 9e50d5a7c4..cd8aab6164 100644
--- a/Kernel/RTC.cpp
+++ b/Kernel/RTC.cpp
@@ -8,11 +8,6 @@ static time_t s_boot_time;
 
 void initialize()
 {
-    u8 cmos_mode = CMOS::read(0x0b);
-    cmos_mode |= 2; // 24 hour mode
-    cmos_mode |= 4; // No BCD mode
-    CMOS::write(0x0b, cmos_mode);
-
     s_boot_time = now();
 }
 
@@ -87,17 +82,39 @@ static unsigned days_in_years_since_epoch(unsigned year)
     return days;
 }
 
+u8 bcd_to_binary(u8 bcd)
+{
+    return (bcd & 0x0F) + ((bcd >> 4) * 10);
+}
+
 void read_registers(unsigned& year, unsigned& month, unsigned& day, unsigned& hour, unsigned& minute, unsigned& second)
 {
     while (update_in_progress())
         ;
 
-    year = (CMOS::read(0x32) * 100) + CMOS::read(0x09);
-    month = CMOS::read(0x08);
-    day = CMOS::read(0x07);
-    hour = CMOS::read(0x04);
-    minute = CMOS::read(0x02);
+    u8 status_b = CMOS::read(0x0b);
+
     second = CMOS::read(0x00);
+    minute = CMOS::read(0x02);
+    hour = CMOS::read(0x04);
+    day = CMOS::read(0x07);
+    month = CMOS::read(0x08);
+    year = CMOS::read(0x09);
+
+    if (!(status_b & 0x04)) {
+        second = bcd_to_binary(second);
+        minute = bcd_to_binary(minute);
+        hour = bcd_to_binary(hour & 0x70);
+        day = bcd_to_binary(day);
+        month = bcd_to_binary(month);
+        year = bcd_to_binary(year);
+    }
+
+    if (!(status_b & 0x02) && (hour & 0x80)) {
+        hour = ((hour & 0x7F) + 12) % 24;
+    }
+
+    year += 2000;
 }
 
 time_t now()