Add the boot graphics resource table as specified in SEC. 5.2.22 of the ACPI specification v. 6.4

This commit adds the BGRT as specified in [SEC. 5.2.22 of the ACPI specification](https://uefi.org/specs/ACPI/6.4/05_ACPI_Software_Programming_Model/ACPI_Software_Programming_Model.html#boot-graphics-resource-table-bgrt). The BGRT is
used for notifying OSPM of any boot graphics displayed by firmware during the boot process.

Signed-off-by: Ethin Probst <ethindp@protonmail.com>

acpi/src/bgrt.rs

@@ -0,0 +1,60 @@
+use crate::{sdt::SdtHeader, AcpiTable};
+use bit_field::BitField;
+
+#[repr(C, packed)]
+#[derive(Clone, Copy)]
+pub struct Bgrt {
+    header: SdtHeader,
+    pub version: u16,
+    status: u8,
+    image_type: u8,
+    pub image_address: u64,
+    image_offset_x: u32,
+    image_offset_y: u32,
+}
+
+impl AcpiTable for Bgrt {
+    fn header(&self) -> &SdtHeader {
+        &self.header
+    }
+}
+
+impl Bgrt {
+    pub fn image_type(&self) -> ImageType {
+        let img_type = self.image_type;
+        match img_type {
+            1 => ImageType::Bitmap,
+            _ => ImageType::Reserved,
+        }
+    }
+
+    pub fn orientation_offset(&self) -> u16 {
+        let status = self.status;
+        match status.get_bits(1 .. 3) {
+            0=> 0,
+            1 => 90,
+            2 => 180,
+            3 => 270,
+            _ => unimplemented!(), // will never happen
+        }
+    }
+
+    pub fn was_displayed(&self) -> bool {
+        let status = self.status;
+        status.get_bit(0)
+    }
+
+    pub fn image_offset(&self) -> (u32, u32) {
+        let x = self.image_offset_x;
+        let y = self.image_offset_y;
+        (x, y)
+    }
+}
+
+#[repr(u8)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub enum ImageType {
+    Bitmap,
+    Reserved,
+}
+

acpi/src/lib.rs

@@ -61,6 +61,7 @@ pub mod madt;
 pub mod mcfg;
 pub mod platform;
 pub mod sdt;
+pub mod bgrt;
 
 pub use crate::{
     fadt::PowerProfile,