From 6b45c59a9ad886bcb2a4c791bdcdc59da68659ba Mon Sep 17 00:00:00 2001
From: Daniel Hammer <daniel@nexlink.cloud>
Date: Sun, 24 May 2026 10:23:16 +0200
Subject: [PATCH] feat: Xhci BIOS-to-OS handoff

---
 kernel/src/Drivers/USB/Xhci.cpp | 97 +++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)

diff --git a/kernel/src/Drivers/USB/Xhci.cpp b/kernel/src/Drivers/USB/Xhci.cpp
index d13c2d6..0d6820f 100644
--- a/kernel/src/Drivers/USB/Xhci.cpp
+++ b/kernel/src/Drivers/USB/Xhci.cpp
@@ -230,6 +230,93 @@ namespace Drivers::USB::Xhci {
 
     static void HandleInterrupt(uint8_t irq);
 
+    // -------------------------------------------------------------------------
+    // BIOS-to-OS handoff (USB Legacy Support)
+    //
+    // Per xHCI spec section 7.1: walk the extended capability list starting at
+    // xECP (HCCPARAMS1[31:16]) to find Cap ID 0x01 (USB Legacy Support). Set
+    // the OS-Owned semaphore, wait for BIOS to clear its semaphore, and then
+    // disable all USB-Legacy SMI sources.
+    //
+    // Without this, BIOS SMI handlers that emulate PS/2 from USB devices stay
+    // active and steal i8042 events, so the built-in keyboard/trackpad input
+    // does not reach the OS until USB activity wakes the SMI handler.
+    // -------------------------------------------------------------------------
+
+    static constexpr uint8_t  XHCI_EXTCAP_LEGACY      = 0x01;
+    static constexpr uint32_t USBLEGSUP_BIOS_OWNED    = (1u << 16);
+    static constexpr uint32_t USBLEGSUP_OS_OWNED      = (1u << 24);
+    static constexpr uint32_t USBLEGCTLSTS_SMI_ENABLES =
+          (1u << 0)   // USB SMI Enable
+        | (1u << 4)   // SMI on Host System Error Enable
+        | (1u << 13)  // SMI on OS Ownership Enable
+        | (1u << 14)  // SMI on PCI Command Enable
+        | (1u << 15); // SMI on BAR Enable
+    static constexpr uint32_t USBLEGCTLSTS_W1C_STATUS =
+          (1u << 20)  // SMI on OS Ownership Change
+        | (1u << 21)  // SMI on PCI Command
+        | (1u << 22); // SMI on BAR
+
+    static void PerformBiosHandoff() {
+        uint32_t hccparams1 = ReadCap(CAP_HCCPARAMS1);
+        uint32_t xecp = (hccparams1 >> 16) & 0xFFFF;
+
+        if (xecp == 0) {
+            KernelLogStream(INFO, "xHCI") << "No extended capabilities (xECP=0)";
+            return;
+        }
+
+        volatile uint32_t* extCap = (volatile uint32_t*)(g_mmioBase + xecp * 4);
+
+        for (int i = 0; i < 64; i++) {
+            uint32_t capReg = *extCap;
+            uint8_t capId = capReg & 0xFF;
+            uint8_t nextOffset = (capReg >> 8) & 0xFF;
+
+            if (capId == XHCI_EXTCAP_LEGACY) {
+                KernelLogStream(INFO, "xHCI") << "USB Legacy Support found, requesting BIOS handoff";
+
+                // Assert OS-Owned. Preserve the BIOS-Owned bit so BIOS sees the
+                // request and can finish cleanly before clearing its own bit.
+                *extCap = capReg | USBLEGSUP_OS_OWNED;
+
+                uint64_t deadline = Timekeeping::GetMilliseconds() + 1000;
+                bool released = false;
+                while (Timekeeping::GetMilliseconds() < deadline) {
+                    if (!(*extCap & USBLEGSUP_BIOS_OWNED)) {
+                        released = true;
+                        break;
+                    }
+                    BusyWaitMs(10);
+                }
+
+                if (!released) {
+                    KernelLogStream(WARNING, "xHCI")
+                        << "BIOS did not release controller in 1s, forcing handoff";
+                    uint32_t v = *extCap;
+                    v &= ~USBLEGSUP_BIOS_OWNED;
+                    v |= USBLEGSUP_OS_OWNED;
+                    *extCap = v;
+                } else {
+                    KernelLogStream(OK, "xHCI") << "BIOS released xHCI ownership";
+                }
+
+                // Disable all USB-Legacy SMI sources and clear any pending
+                // W1C status bits. Preserves RsvdP bits via read-modify-write.
+                volatile uint32_t* ctlsts = extCap + 1;
+                uint32_t v = *ctlsts;
+                v &= ~USBLEGCTLSTS_SMI_ENABLES;
+                v |= USBLEGCTLSTS_W1C_STATUS;
+                *ctlsts = v;
+
+                return;
+            }
+
+            if (nextOffset == 0) return;
+            extCap += nextOffset;
+        }
+    }
+
     // -------------------------------------------------------------------------
     // MSI setup (same pattern as E1000E)
     // -------------------------------------------------------------------------
@@ -1011,6 +1098,11 @@ namespace Drivers::USB::Xhci {
         if (g_maxSlots > MAX_SLOTS) g_maxSlots = MAX_SLOTS;
         if (g_maxPorts > MAX_PORTS) g_maxPorts = MAX_PORTS;
 
+        // Tell BIOS to release the controller and disable USB-Legacy SMIs.
+        // Must run before we halt/reset so BIOS gets a chance to shut down
+        // its own use of the controller cleanly.
+        PerformBiosHandoff();
+
         // Halt controller
         uint32_t usbcmd = ReadOp(OP_USBCMD);
         usbcmd &= ~USBCMD_RS;
@@ -1259,6 +1351,11 @@ namespace Drivers::USB::Xhci {
             g_maxPorts = MAX_PORTS;
         }
 
+        // -----------------------------------------------------------------
+        // Step 4.5: BIOS-to-OS handoff (USB Legacy Support)
+        // -----------------------------------------------------------------
+        PerformBiosHandoff();
+
         // -----------------------------------------------------------------
         // Step 5: Halt controller
         // -----------------------------------------------------------------