Kernel: Implement a PCI Serial Device driver

This simple driver simply finds a device in a device definitions list
and then sets up a SerialDevice instance based on the definition.

The driver currently only supports "WCH CH382 2S" pci serial boards,
as that is the only device available for me to test with, but most
other pci serial devices should be as easily addable as adding a
board_definitions entry.

Kernel/Devices/PCISerialDevice.cpp

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2021, Idan Horowitz <idan.horowitz@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Devices/PCISerialDevice.h>
+
+namespace Kernel {
+
+static SerialDevice* s_the = nullptr;
+
+void PCISerialDevice::detect()
+{
+    PCI::enumerate([&](const PCI::Address& address, PCI::ID id) {
+        if (address.is_null())
+            return;
+
+        // HACK: There's currently no way to break out of PCI::enumerate, so we just early return if we already initialized the pci serial device
+        if (is_available())
+            return;
+
+        for (auto& board_definition : board_definitions) {
+            if (board_definition.device_id != id)
+                continue;
+
+            auto bar_base = PCI::get_BAR(address, board_definition.pci_bar) & ~1;
+            // FIXME: We should support more than 1 PCI serial port (per card/multiple devices)
+            s_the = new SerialDevice(IOAddress(bar_base + board_definition.first_offset), 64);
+            if (board_definition.baud_rate != SerialDevice::Baud::Baud38400) // non-default baud
+                s_the->set_baud(board_definition.baud_rate);
+
+            dmesgln("PCISerialDevice: Found {} @ {}", board_definition.name, address);
+            return;
+        }
+    });
+}
+
+SerialDevice& PCISerialDevice::the()
+{
+    VERIFY(s_the);
+    return *s_the;
+}
+
+bool PCISerialDevice::is_available()
+{
+    return s_the;
+}
+
+}