Kernel: Change PCI access commandline option to also represent no access

This change allow the user to request the kernel to not use any PCI
resources/devices at all.

Also, don't try to initialize devices that rely on PCI if disabled.

Base/usr/share/man/man7/boot_parameters.md

@@ -56,7 +56,8 @@ List of options:
 
 * **`panic`** - This parameter expects **`halt`** or **`shutdown`**. This is particularly useful in CI contexts.
 
-* **`pci_ecam`** - This parameter expects **`on`** or **`off`**.
+* **`pci`** - This parameter expects **`ecam`**, **`io`** or **`none`**. When selecting **`none`**
+  the kernel will not use PCI resources/devices.
 
 * **`root`** - This parameter configures the device to use as the root file system. It defaults to **`/dev/hda`** if unspecified.
 

Kernel/Bus/PCI/Initializer.cpp

@@ -36,6 +36,7 @@ UNMAP_AFTER_INIT static PCIAccessLevel detect_optimal_access_type()
 
 UNMAP_AFTER_INIT void initialize()
 {
+    VERIFY(kernel_command_line().pci_access_level() != PCIAccessLevel::None);
     switch (detect_optimal_access_type()) {
     case PCIAccessLevel::MemoryAddressing: {
         auto mcfg = ACPI::Parser::the()->find_table("MCFG");

Kernel/CommandLine.cpp

@@ -142,14 +142,21 @@ UNMAP_AFTER_INIT bool CommandLine::is_vmmouse_enabled() const
 
 UNMAP_AFTER_INIT PCIAccessLevel CommandLine::pci_access_level() const
 {
-    auto value = lookup("pci_ecam"sv).value_or("on"sv);
+    auto value = lookup("pci"sv).value_or("ecam"sv);
-    if (value == "on"sv)
+    if (value == "ecam"sv)
         return PCIAccessLevel::MemoryAddressing;
-    if (value == "off"sv)
+    if (value == "io"sv)
         return PCIAccessLevel::IOAddressing;
+    if (value == "none"sv)
+        return PCIAccessLevel::None;
     PANIC("Unknown PCI ECAM setting: {}", value);
 }
 
+UNMAP_AFTER_INIT bool CommandLine::is_pci_disabled() const
+{
+    return lookup("pci"sv).value_or("ecam"sv) == "none"sv;
+}
+
 UNMAP_AFTER_INIT bool CommandLine::is_legacy_time_enabled() const
 {
     return lookup("time"sv).value_or("modern"sv) == "legacy"sv;

Kernel/CommandLine.h

@@ -31,6 +31,7 @@ enum class AcpiFeatureLevel {
 };
 
 enum class PCIAccessLevel {
+    None,
     IOAddressing,
     MemoryAddressing,
 };
@@ -70,6 +71,7 @@ public:
     [[nodiscard]] bool is_physical_networking_disabled() const;
     [[nodiscard]] bool is_vmmouse_enabled() const;
     [[nodiscard]] PCIAccessLevel pci_access_level() const;
+    [[nodiscard]] bool is_pci_disabled() const;
     [[nodiscard]] bool is_legacy_time_enabled() const;
     [[nodiscard]] bool is_pc_speaker_enabled() const;
     [[nodiscard]] FrameBufferDevices are_framebuffer_devices_enabled() const;

Kernel/init.cpp

@@ -299,8 +299,10 @@ void init_stage2(void*)
     }
 
     // Initialize the PCI Bus as early as possible, for early boot (PCI based) serial logging
-    PCI::initialize();
+    if (!kernel_command_line().is_pci_disabled()) {
-    PCISerialDevice::detect();
+        PCI::initialize();
+        PCISerialDevice::detect();
+    }
 
     VirtualFileSystem::initialize();
 
@@ -321,10 +323,14 @@ void init_stage2(void*)
 
     auto boot_profiling = kernel_command_line().is_boot_profiling_enabled();
 
-    USB::USBManagement::initialize();
+    if (!kernel_command_line().is_pci_disabled()) {
+        USB::USBManagement::initialize();
+    }
     FirmwareSysFSDirectory::initialize();
 
-    VirtIO::detect();
+    if (!kernel_command_line().is_pci_disabled()) {
+        VirtIO::detect();
+    }
 
     NetworkingManagement::the().initialize();
     Syscall::initialize();