feat: Bochs VBE linear framebuffer support

Cargo.toml

@@ -216,6 +216,10 @@ virtio-vsock = ["virtio"]
 ## This is only useful on PCs (x86-64).
 vga = []
 
+## Enables the _Bochs Graphics Adapter_ (BGA) driver.
+##
+## This provides a linear framebuffer for pixel graphics and is primarily useful in QEMU/Bochs environments (x86-64).
+bga = ["pci"]
 #! ### Performance Features
 
 ## Disables putting the CPU to sleep.

src/arch/x86_64/kernel/bga.rs

@@ -0,0 +1,91 @@
+use core::sync::atomic::{AtomicU64, Ordering};
+
+use memory_addresses::{PhysAddr, VirtAddr};
+use pci_types::{Bar, CommandRegister};
+use x86_64::instructions::port::Port;
+
+use crate::arch::x86_64::mm::paging;
+use crate::arch::x86_64::mm::paging::{BasePageSize, PageTableEntryFlags, PageTableEntryFlagsExt};
+use crate::drivers::pci::PciDevice;
+use crate::kernel::pci::PciConfigRegion;
+
+static FRAMEBUFFER_PHYS: AtomicU64 = AtomicU64::new(0);
+
+const VBE_DISPI_IOPORT_INDEX: u16 = 0x01ce;
+const VBE_DISPI_IOPORT_DATA: u16 = 0x01cf;
+
+const VBE_DISPI_INDEX_ID: u16 = 0;
+const VBE_DISPI_INDEX_XRES: u16 = 1;
+const VBE_DISPI_INDEX_YRES: u16 = 2;
+const VBE_DISPI_INDEX_BPP: u16 = 3;
+const VBE_DISPI_INDEX_ENABLE: u16 = 4;
+
+const VBE_DISPI_DISABLED: u16 = 0x00;
+const VBE_DISPI_ENABLED: u16 = 0x01;
+const VBE_DISPI_LFB_ENABLED: u16 = 0x40;
+const VBE_DISPI_ID5: u16 = 0xb0c5;
+
+pub fn init_device(adapter: &PciDevice<PciConfigRegion>) {
+	//To Do: Detect Resolution automatically
+	let width: u16 = 640;
+	let height: u16 = 400;
+	let bpp: u16 = 32;
+
+	unsafe {
+		let mut index_port: Port<u16> = Port::new(VBE_DISPI_IOPORT_INDEX);
+		let mut data_port: Port<u16> = Port::new(VBE_DISPI_IOPORT_DATA);
+
+		index_port.write(VBE_DISPI_INDEX_ID);
+		let bga_version = data_port.read();
+
+		if bga_version != VBE_DISPI_ID5 {
+			error!("Unsupported BGA version: {bga_version:#06x}");
+			return;
+		}
+
+		index_port.write(VBE_DISPI_INDEX_ENABLE);
+		data_port.write(VBE_DISPI_DISABLED);
+
+		index_port.write(VBE_DISPI_INDEX_XRES);
+		data_port.write(width);
+
+		index_port.write(VBE_DISPI_INDEX_YRES);
+		data_port.write(height);
+
+		index_port.write(VBE_DISPI_INDEX_BPP);
+		data_port.write(bpp);
+
+		index_port.write(VBE_DISPI_INDEX_ENABLE);
+		data_port.write(VBE_DISPI_ENABLED | VBE_DISPI_LFB_ENABLED);
+	}
+
+	adapter.set_command(CommandRegister::MEMORY_ENABLE);
+
+	let (phys_addr, size) = match adapter.get_bar(0) {
+		Some(Bar::Memory32 { address, size, .. }) => (u64::from(address), size as usize),
+		Some(Bar::Memory64 { address, size, .. }) => (address, size as usize),
+		_ => return,
+	};
+
+	FRAMEBUFFER_PHYS.store(phys_addr, Ordering::Release);
+
+	assert!(
+		size % 4096 == 0,
+		"Framebuffer size must be a multiple of 4096 bytes"
+	);
+	let page_count = size / 4096;
+
+	let mut flags = PageTableEntryFlags::empty();
+	flags.device().writable().execute_disable();
+	flags.insert(PageTableEntryFlags::USER_ACCESSIBLE);
+	paging::map::<BasePageSize>(
+		VirtAddr::new(phys_addr),
+		PhysAddr::new(phys_addr),
+		page_count,
+		flags,
+	);
+}
+
+pub fn get_framebuffer_address() -> u64 {
+	FRAMEBUFFER_PHYS.load(Ordering::Acquire)
+}

src/arch/x86_64/kernel/mod.rs

@@ -15,6 +15,8 @@ use crate::env::{self, is_uhyve};
 #[cfg(feature = "acpi")]
 pub mod acpi;
 pub mod apic;
+#[cfg(feature = "bga")]
+pub mod bga;
 pub mod core_local;
 pub mod gdt;
 pub mod interrupts;

src/drivers/pci.rs

@@ -459,6 +459,19 @@ pub(crate) fn init(handlers: &mut InterruptHandlerMap) {
 				Err(err) => error!("Could not initialize rtl8139 device: {err}"),
 			}
 		}
+
+		#[cfg(all(target_arch = "x86_64", feature = "bga"))]
+		for adapter in PCI_DEVICES.finalize().iter().filter(|x| {
+			let (vendor_id, device_id) = x.id();
+			vendor_id == 0x1234 && device_id == 0x1111
+		}) {
+			info!(
+				"Found Bochs VGA device with device id {:#x}",
+				adapter.device_id()
+			);
+
+			crate::kernel::bga::init_device(adapter);
+		}
 		PCI_DRIVERS.finalize();
 	});
 }

src/syscalls/system.rs

@@ -6,3 +6,18 @@ use crate::arch::mm::paging::{BasePageSize, PageSize};
 pub extern "C" fn sys_getpagesize() -> i32 {
 	BasePageSize::SIZE.try_into().unwrap()
 }
+
+/// Returns the address of the framebuffer, if available. Returns 0 if no framebuffer is available.
+#[cfg(all(target_arch = "x86_64", feature = "bga"))]
+#[hermit_macro::system]
+#[unsafe(no_mangle)]
+pub extern "C" fn sys_get_framebuffer() -> u64 {
+	crate::kernel::bga::get_framebuffer_address()
+}
+
+#[cfg(not(all(target_arch = "x86_64", feature = "bga")))]
+#[hermit_macro::system]
+#[unsafe(no_mangle)]
+pub extern "C" fn sys_get_framebuffer() -> u64 {
+	0
+}