Kernel: Move all Graphics-related code into Devices/GPU directory

Like the HID, Audio and Storage subsystem, the Graphics subsystem (which
handles GPUs technically) exposes unix device files (typically in /dev).
To ensure consistency across the repository, move all related files to a
new directory under Kernel/Devices called "GPU".

Also remove the redundant "GPU" word from the VirtIO driver directory,
and the word "Graphics" from GraphicsManagement.{h,cpp} filenames.

Kernel/Devices/GPU/Intel/Auxiliary/GMBusConnector.cpp

@@ -0,0 +1,123 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Arch/Delay.h>
+#include <Kernel/Devices/GPU/Intel/Auxiliary/GMBusConnector.h>
+#include <Kernel/Memory/PhysicalAddress.h>
+
+namespace Kernel {
+
+enum class GMBusStatus {
+    TransactionCompletion,
+    HardwareReady
+};
+
+enum GMBusCycle {
+    Wait = 1,
+    Stop = 4,
+};
+
+ErrorOr<NonnullOwnPtr<GMBusConnector>> GMBusConnector::create_with_physical_address(PhysicalAddress gmbus_start_address)
+{
+    auto registers_mapping = TRY(map_typed<GMBusRegisters volatile>(gmbus_start_address, sizeof(GMBusRegisters), Memory::Region::Access::ReadWrite));
+    return adopt_nonnull_own_or_enomem(new (nothrow) GMBusConnector(move(registers_mapping)));
+}
+
+GMBusConnector::GMBusConnector(Memory::TypedMapping<GMBusRegisters volatile> registers_mapping)
+    : m_gmbus_registers(move(registers_mapping))
+{
+    set_default_rate();
+    set_pin_pair(PinPair::DedicatedAnalog);
+}
+
+bool GMBusConnector::wait_for(GMBusStatus desired_status, size_t milliseconds_timeout)
+{
+    VERIFY(m_access_lock.is_locked());
+    size_t milliseconds_passed = 0;
+    while (1) {
+        if (milliseconds_timeout < milliseconds_passed)
+            return false;
+        full_memory_barrier();
+        u32 status = m_gmbus_registers->status;
+        full_memory_barrier();
+        VERIFY(!(status & (1 << 10))); // error happened
+        switch (desired_status) {
+        case GMBusStatus::HardwareReady:
+            if (status & (1 << 11))
+                return true;
+            break;
+        case GMBusStatus::TransactionCompletion:
+            if (status & (1 << 14))
+                return true;
+            break;
+        default:
+            VERIFY_NOT_REACHED();
+        }
+        microseconds_delay(1000);
+        milliseconds_passed++;
+    }
+}
+
+ErrorOr<void> GMBusConnector::write(unsigned address, u32 data)
+{
+    VERIFY(address < 256);
+    SpinlockLocker locker(m_access_lock);
+    full_memory_barrier();
+    m_gmbus_registers->data = data;
+    full_memory_barrier();
+    m_gmbus_registers->command = ((address << 1) | (1 << 16) | (GMBusCycle::Wait << 25) | (1 << 30));
+    full_memory_barrier();
+    if (!wait_for(GMBusStatus::TransactionCompletion, 250))
+        return Error::from_errno(EBUSY);
+    return {};
+}
+
+void GMBusConnector::set_default_rate()
+{
+    // FIXME: Verify GMBUS Rate Select is set only when GMBUS is idle
+    SpinlockLocker locker(m_access_lock);
+    // Set the rate to 100KHz
+    m_gmbus_registers->clock = m_gmbus_registers->clock & ~(0b111 << 8);
+}
+
+void GMBusConnector::set_pin_pair(PinPair pin_pair)
+{
+    // FIXME: Verify GMBUS is idle
+    SpinlockLocker locker(m_access_lock);
+    m_gmbus_registers->clock = (m_gmbus_registers->clock & (~0b111)) | (pin_pair & 0b111);
+}
+
+ErrorOr<void> GMBusConnector::read(unsigned address, u8* buf, size_t length)
+{
+    VERIFY(address < 256);
+    SpinlockLocker locker(m_access_lock);
+    size_t nread = 0;
+    auto read_set = [&] {
+        full_memory_barrier();
+        u32 data = m_gmbus_registers->data;
+        full_memory_barrier();
+        for (size_t index = 0; index < 4; index++) {
+            if (nread == length)
+                break;
+            buf[nread] = (data >> (8 * index)) & 0xFF;
+            nread++;
+        }
+    };
+
+    full_memory_barrier();
+    m_gmbus_registers->command = (1 | (address << 1) | (length << 16) | (GMBusCycle::Wait << 25) | (1 << 30));
+    full_memory_barrier();
+    while (nread < length) {
+        if (!wait_for(GMBusStatus::HardwareReady, 250))
+            return Error::from_errno(EBUSY);
+        read_set();
+    }
+    if (!wait_for(GMBusStatus::TransactionCompletion, 250))
+        return Error::from_errno(EBUSY);
+    return {};
+}
+
+}