[gierens]

This adds sdt::dmar module containing the types for parsing ACPI DMAR
tables. It follows the definitions in the "Intel(R) Virtualization
Technology for Directed I/O Architecture Specification"
(https://software.intel.com/content/dam/develop/public/us/en/documents/vt-directed-io-spec.pdf)
section 8.1.

At the root is the Dmar with the function entries, returning an iterator over
the DmarEntry enum. This can contain the structs DrhdEntry, RmrrEntry,
AtsrEntry, RhsaEntry, AnddEntry, SatcEntry, or SidpEntry. Some of these
contain DeviceScopes also returned as iterator.

For testing I created a small repo with a minimal kernel and runner program
that you can find here: https://github.com/gierens/acpi-dmar-demo
It just sets up the logger, page table, allocator, and then parses the ACPI
tables, of which it then prints the DMAR, entries, and device scopes.
cargo run launches the kernel in QEMU with
-machine q35,accel=kvm,kernel_irqchip=split -device intel-iommu,intremap=on,caching-mode=on
(see https://github.com/gierens/acpi-dmar-demo/blob/main/src/main.rs#L31-L34)
which yields a single DRHD entry in DMAR.

Using the following code:

let dmar = platform.tables.find_table::<Dmar>().unwrap();
let dmar = dmar.get();
log::info!("DMAR: {dmar:?}");
for entry in dmar.entries() {
    log::info!("DMAR entry: {entry:?}");
    if let DmarEntry::Drhd(drhd) = entry {
        for scope in drhd.device_scopes() {
            log::info!("Device scope: {scope:?}, path: {:?}", scope.path());
        }
    }
}

in kernel/src/main.rs (see https://github.com/gierens/acpi-dmar-demo/blob/main/kernel/src/main.rs#L42-L52) it then prints:

INFO : DMAR: Dmar { header: SdtHeader { signature: "DMAR", length: 120, revision: 1, checksum: 4, oem_id: [66, 79, 67, 72, 83, 32], oem_table_id: [66, 88, 80, 67, 32, 32, 32, 32], oem_revision: 1, creator_id: [66, 88, 80, 67], creator_revision: 1 }, host_address_width: 47, flags: 1, _reserved: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], _pinned: PhantomPinned }
INFO : DMAR entry: Drhd(DrhdEntry { header: DmarEntryHeader { entry_type: 0, length: 72 }, flags: 0, size: 0, segment_number: 0, register_base_address: 4275634176 })
INFO : Device scope: DeviceScope { scope_type: 3, length: 8, flags: 0, _reserved: 0, enumeration_id: 0, start_bus_number: 255 }, path: Ok([DeviceScopePathComponent { device: 0, function: 0 }])
INFO : Device scope: DeviceScope { scope_type: 1, length: 8, flags: 0, _reserved: 0, enumeration_id: 0, start_bus_number: 0 }, path: Ok([DeviceScopePathComponent { device: 0, function: 0 }])
INFO : Device scope: DeviceScope { scope_type: 1, length: 8, flags: 0, _reserved: 0, enumeration_id: 0, start_bus_number: 0 }, path: Ok([DeviceScopePathComponent { device: 1, function: 0 }])
INFO : Device scope: DeviceScope { scope_type: 1, length: 8, flags: 0, _reserved: 0, enumeration_id: 0, start_bus_number: 0 }, path: Ok([DeviceScopePathComponent { device: 2, function: 0 }])
INFO : Device scope: DeviceScope { scope_type: 1, length: 8, flags: 0, _reserved: 0, enumeration_id: 0, start_bus_number: 0 }, path: Ok([DeviceScopePathComponent { device: 31, function: 0 }])
INFO : Device scope: DeviceScope { scope_type: 1, length: 8, flags: 0, _reserved: 0, enumeration_id: 0, start_bus_number: 0 }, path: Ok([DeviceScopePathComponent { device: 31, function: 2 }])
INFO : Device scope: DeviceScope { scope_type: 1, length: 8, flags: 0, _reserved: 0, enumeration_id: 0, start_bus_number: 0 }, path: Ok([DeviceScopePathComponent { device: 31, function: 3 }])

This fixes #105 , probably better to open another issue for IVRS