Kernel/Graphics: Introduce support for QEMU isa-vga device

This device is supposed to be used in microvm and ISA-PC machine types,
and we assume that if we are able to probe for the QEMU BGA version of
0xB0C5, then we have an existing ISA Bochs VGA adapter to utilize.
To ensure we don't instantiate the driver for non isa-vga devices, we
try to ensure that PCI is disabled because hardware IO test probe failed
so we can be sure that we use this special handling code only in the
QEMU microvm and ISA-PC machine types. Unfortunately, this means that if
for some reason the isa-vga device is attached for the i440FX or Q35
machine types, we simply are not able to drive the device in such setups
at all.

To determine the amount of VRAM being available, we read VBE register at
offset 0xA. That register holds the amount of VRAM divided by 64K, so we
need to multiply the value in our code to use the actual VRAM size value
again.

The isa-vga device requires us to hardcode the framebuffer physical
address to 0xE0000000, and that address is not expected to change in the
future as many other projects rely on the isa-vga framebuffer to be
present at that physical memory address.

Kernel/Arch/x86/Hypervisor/BochsDisplayConnector.cpp

@@ -7,6 +7,7 @@
 #include <AK/Platform.h>
 #include <Kernel/Arch/x86/Hypervisor/BochsDisplayConnector.h>
 #include <Kernel/Arch/x86/IO.h>
+#include <Kernel/Bus/PCI/Access.h>
 #include <Kernel/Debug.h>
 #include <Kernel/Devices/DeviceManagement.h>
 #include <Kernel/Graphics/Bochs/Definitions.h>
@@ -15,6 +16,45 @@
 
 namespace Kernel {
 
+static void set_register_with_io(u16 index, u16 data)
+{
+    IO::out16(VBE_DISPI_IOPORT_INDEX, index);
+    IO::out16(VBE_DISPI_IOPORT_DATA, data);
+}
+
+static u16 get_register_with_io(u16 index)
+{
+    IO::out16(VBE_DISPI_IOPORT_INDEX, index);
+    return IO::in16(VBE_DISPI_IOPORT_DATA);
+}
+
+LockRefPtr<BochsDisplayConnector> BochsDisplayConnector::try_create_for_vga_isa_connector()
+{
+    VERIFY(PCI::Access::is_hardware_disabled());
+    BochsDisplayConnector::IndexID index_id = get_register_with_io(0);
+    if (index_id != VBE_DISPI_ID5)
+        return {};
+
+    auto video_ram_64k_chunks_count = get_register_with_io(to_underlying(BochsDISPIRegisters::VIDEO_RAM_64K_CHUNKS_COUNT));
+    if (video_ram_64k_chunks_count == 0 || video_ram_64k_chunks_count == 0xffff) {
+        dmesgln("Graphics: Bochs ISA VGA compatible adapter does not indicate amount of VRAM, default to 8 MiB");
+        video_ram_64k_chunks_count = (8 * MiB) / (64 * KiB);
+    } else {
+        dmesgln("Graphics: Bochs ISA VGA compatible adapter indicates {} bytes of VRAM", video_ram_64k_chunks_count * (64 * KiB));
+    }
+
+    // Note: The default physical address for isa-vga framebuffer in QEMU is 0xE0000000.
+    // Since this is probably hardcoded at other OSes in their guest drivers,
+    // we can assume this is going to stay the same framebuffer physical address for
+    // this device and will not be changed in the future.
+    auto device_or_error = DeviceManagement::try_create_device<BochsDisplayConnector>(PhysicalAddress(0xE0000000), video_ram_64k_chunks_count * (64 * KiB));
+    VERIFY(!device_or_error.is_error());
+    auto connector = device_or_error.release_value();
+    MUST(connector->create_attached_framebuffer_console());
+    MUST(connector->initialize_edid_for_generic_monitor({}));
+    return connector;
+}
+
 NonnullLockRefPtr<BochsDisplayConnector> BochsDisplayConnector::must_create(PhysicalAddress framebuffer_address, size_t framebuffer_resource_size, bool virtual_box_hardware)
 {
     auto device_or_error = DeviceManagement::try_create_device<BochsDisplayConnector>(framebuffer_address, framebuffer_resource_size);
@@ -41,18 +81,6 @@ ErrorOr<void> BochsDisplayConnector::create_attached_framebuffer_console()
     return {};
 }
 
-static void set_register_with_io(u16 index, u16 data)
-{
-    IO::out16(VBE_DISPI_IOPORT_INDEX, index);
-    IO::out16(VBE_DISPI_IOPORT_DATA, data);
-}
-
-static u16 get_register_with_io(u16 index)
-{
-    IO::out16(VBE_DISPI_IOPORT_INDEX, index);
-    return IO::in16(VBE_DISPI_IOPORT_DATA);
-}
-
 BochsDisplayConnector::IndexID BochsDisplayConnector::index_id() const
 {
     return get_register_with_io(0);

Kernel/Arch/x86/Hypervisor/BochsDisplayConnector.h

@@ -20,10 +20,13 @@ class BochsDisplayConnector
     : public DisplayConnector {
     friend class BochsGraphicsAdapter;
     friend class DeviceManagement;
+    friend class GraphicsManagement;
 
 public:
     AK_TYPEDEF_DISTINCT_ORDERED_ID(u16, IndexID);
 
+    static LockRefPtr<BochsDisplayConnector> try_create_for_vga_isa_connector();
+
     static NonnullLockRefPtr<BochsDisplayConnector> must_create(PhysicalAddress framebuffer_address, size_t framebuffer_resource_size, bool virtual_box_hardware);
 
 private:

Kernel/Bus/PCI/Access.cpp

@@ -40,6 +40,11 @@ bool Access::is_initialized()
     return (s_access != nullptr);
 }
 
+bool Access::is_hardware_disabled()
+{
+    return g_pci_access_io_probe_failed;
+}
+
 bool Access::is_disabled()
 {
     return g_pci_access_is_disabled_from_commandline || g_pci_access_io_probe_failed;

Kernel/Bus/PCI/Access.h

@@ -30,6 +30,7 @@ public:
     static Access& the();
     static bool is_initialized();
     static bool is_disabled();
+    static bool is_hardware_disabled();
 
     void write8_field(Address address, u32 field, u8 value);
     void write16_field(Address address, u32 field, u16 value);

Kernel/Graphics/Bochs/Definitions.h

@@ -34,6 +34,7 @@ enum class BochsDISPIRegisters {
     VIRT_HEIGHT = 0x7,
     X_OFFSET = 0x8,
     Y_OFFSET = 0x9,
+    VIDEO_RAM_64K_CHUNKS_COUNT = 0xA,
 };
 
 struct [[gnu::packed]] DISPIInterface {
@@ -47,6 +48,7 @@ struct [[gnu::packed]] DISPIInterface {
     u16 virt_height;
     u16 x_offset;
     u16 y_offset;
+    u16 vram_64k_chunks_count;
 };
 
 struct [[gnu::packed]] ExtensionRegisters {

Kernel/Graphics/GraphicsManagement.cpp

@@ -7,6 +7,9 @@
 #include <AK/Singleton.h>
 #include <Kernel/Arch/Delay.h>
 #include <Kernel/Arch/x86/IO.h>
+#if ARCH(I386) || ARCH(X86_64)
+#    include <Kernel/Arch/x86/Hypervisor/BochsDisplayConnector.h>
+#endif
 #include <Kernel/Bus/PCI/API.h>
 #include <Kernel/Bus/PCI/IDs.h>
 #include <Kernel/CommandLine.h>
@@ -206,6 +209,25 @@ UNMAP_AFTER_INIT bool GraphicsManagement::initialize()
         return true;
     }
 
+    // Note: Don't try to initialize an ISA Bochs VGA adapter if PCI hardware is
+    // present but the user decided to disable its usage nevertheless.
+    // Otherwise we risk using the Bochs VBE driver on a wrong physical address
+    // for the framebuffer.
+    if (PCI::Access::is_hardware_disabled() && !(graphics_subsystem_mode == CommandLine::GraphicsSubsystemMode::Limited && !multiboot_framebuffer_addr.is_null() && multiboot_framebuffer_type == MULTIBOOT_FRAMEBUFFER_TYPE_RGB)) {
+#if ARCH(I386) || ARCH(X86_64)
+        auto vga_isa_bochs_display_connector = BochsDisplayConnector::try_create_for_vga_isa_connector();
+        if (vga_isa_bochs_display_connector) {
+            dmesgln("Graphics: Using a Bochs ISA VGA compatible adapter");
+            MUST(vga_isa_bochs_display_connector->set_safe_mode_setting());
+            m_platform_board_specific_display_connector = vga_isa_bochs_display_connector;
+            dmesgln("Graphics: Invoking manual blanking with VGA ISA ports");
+            SpinlockLocker locker(m_main_vga_lock);
+            IO::out8(0x3c0, 0x20);
+            return true;
+        }
+#endif
+    }
+
     if (graphics_subsystem_mode == CommandLine::GraphicsSubsystemMode::Limited && !multiboot_framebuffer_addr.is_null() && multiboot_framebuffer_type == MULTIBOOT_FRAMEBUFFER_TYPE_RGB) {
         initialize_preset_resolution_generic_display_connector();
         return true;

Kernel/Graphics/GraphicsManagement.h

@@ -56,6 +56,8 @@ private:
     // Note: This is only used when booting with kernel commandline that includes "graphics_subsystem_mode=limited"
     LockRefPtr<GenericDisplayConnector> m_preset_resolution_generic_display_connector;
 
+    LockRefPtr<DisplayConnector> m_platform_board_specific_display_connector;
+
     unsigned m_current_minor_number { 0 };
 
     SpinlockProtected<IntrusiveList<&DisplayConnector::m_list_node>> m_display_connector_nodes { LockRank::None };