acpi_tables: fix the access_size of GenericAddress

Without the fix, the code gives
    1 for Byte access
    2 for Word access
    4 for Dword access
    8 for QWord access.

However, As per ACPI 6.4 spec Sec.5.2.3.2 [1], the access_size should
be
    1 for Byte access
    2 for Word access
    3 for Dword access
    4 for QWord access.

The fix takes QEMU's implementation[2] as a reference. A related
patch[3] has been merged into crosvm.

[1] https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/05_ACPI_Software_Programming_Model/ACPI_Software_Programming_Model.html#generic-address-structure-gas

[2] https://github.com/qemu/qemu/blob/6a4180af9686830d88c387baab6d79563ce42a15/hw/acpi/erst.c#L218

[3] https://chromium-review.googlesource.com/c/crosvm/crosvm/+/5394229

Signed-off-by: Changyuan Lyu <changyuanl@google.com>

src/sdt.rs

@@ -25,7 +25,7 @@ impl GenericAddress {
             address_space_id: 1,
             register_bit_width: 8 * core::mem::size_of::<T>() as u8,
             register_bit_offset: 0,
-            access_size: core::mem::size_of::<T>() as u8,
+            access_size: core::mem::size_of::<T>().trailing_zeros() as u8 + 1,
             address: u64::from(address),
         }
     }
@@ -34,7 +34,7 @@ impl GenericAddress {
             address_space_id: 0,
             register_bit_width: 8 * core::mem::size_of::<T>() as u8,
             register_bit_offset: 0,
-            access_size: core::mem::size_of::<T>() as u8,
+            access_size: core::mem::size_of::<T>().trailing_zeros() as u8 + 1,
             address,
         }
     }
@@ -151,7 +151,7 @@ impl Aml for Sdt {
 
 #[cfg(test)]
 mod tests {
-    use super::Sdt;
+    use super::{GenericAddress, Sdt};
 
     #[test]
     fn test_sdt() {
@@ -168,4 +168,16 @@ mod tests {
             .fold(0u8, |acc, x| acc.wrapping_add(*x));
         assert_eq!(sum, 0);
     }
+
+    #[test]
+    fn test_generic_address_access_size() {
+        let byte_mmio = GenericAddress::mmio_address::<u8>(0x1000);
+        assert_eq!(byte_mmio.access_size, 1);
+        let word_mmio = GenericAddress::mmio_address::<u16>(0x1000);
+        assert_eq!(word_mmio.access_size, 2);
+        let dword_mmio = GenericAddress::mmio_address::<u32>(0x1000);
+        assert_eq!(dword_mmio.access_size, 3);
+        let qword_mmio = GenericAddress::mmio_address::<u64>(0x1000);
+        assert_eq!(qword_mmio.access_size, 4);
+    }
 }