From 28bd9cf3535ddcf06cce91a8a210d83e573fa8a8 Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Wed, 19 Aug 2026 18:46:09 +0300
Subject: [PATCH] Kernel: Fix PS/2 scancode set detection logic

If we cannot determine current scancode set because either the keyboard
does not respond or responds with bogus value, assume scancode set 1 and
mark the scancode set as uncertain. If we receive the byte 0xF0 while
having the uncertain flag set, swap to scancode set 2. 0xF0 is unused in
scancode set 1 but indicates key release in scancode set 2, so it will
be sent after every key press.
---
 kernel/include/kernel/Input/PS2/Keyboard.h |  1 +
 kernel/kernel/Input/PS2/Keyboard.cpp       | 17 +++++++++++++++--
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/kernel/include/kernel/Input/PS2/Keyboard.h b/kernel/include/kernel/Input/PS2/Keyboard.h
index 81c8eb02..911f4f49 100644
--- a/kernel/include/kernel/Input/PS2/Keyboard.h
+++ b/kernel/include/kernel/Input/PS2/Keyboard.h
@@ -36,6 +36,7 @@ namespace Kernel::Input
 		uint8_t m_byte_index { 0 };
 		bool m_basic { false };
 
+		bool m_scancode_set_uncertain { false };
 		uint8_t m_scancode_set { 0xFF };
 		uint16_t m_modifiers { 0 };
 
diff --git a/kernel/kernel/Input/PS2/Keyboard.cpp b/kernel/kernel/Input/PS2/Keyboard.cpp
index 37142245..693e3949 100644
--- a/kernel/kernel/Input/PS2/Keyboard.cpp
+++ b/kernel/kernel/Input/PS2/Keyboard.cpp
@@ -53,8 +53,9 @@ namespace Kernel::Input
 
 		if (command_data[0] == Command::CONFIG_SCANCODE_SET && m_scancode_set >= 0xFE)
 		{
-			dwarnln("Could not detect scancode set, assuming 2");
-			m_scancode_set = 2;
+			dwarnln("Could not detect scancode set, assuming 1");
+			m_scancode_set_uncertain = true;
+			m_scancode_set = 1;
 			m_keymap.initialize(m_scancode_set);
 			append_command_queue(PS2::DeviceCommand::ENABLE_SCANNING, 0);
 		}
@@ -89,6 +90,7 @@ namespace Kernel::Input
 			else
 			{
 				dwarnln("Could not detect scancode set, assuming 1");
+				m_scancode_set_uncertain = true;
 				m_scancode_set = 1;
 			}
 			m_keymap.initialize(m_scancode_set);
@@ -103,6 +105,17 @@ namespace Kernel::Input
 			return;
 		}
 
+		// If we could not detect scancode set, we assume it to be 1
+		// If we get byte 0xF0 which is indicates release in scancode set 2
+		// and nothing in scancode set 1, switch to scancode set 2
+		if (m_scancode_set_uncertain && byte == 0xF0)
+		{
+			dprintln("Switching to scancode set 2");
+			m_scancode_set_uncertain = false;
+			m_scancode_set = 2;
+			m_keymap.initialize(m_scancode_set);
+		}
+
 		m_byte_buffer[m_byte_index++] = byte;
 		if (byte == 0xE0)
 			return;