pcid: Explain why PciBar is used instead of pcid_types::Bar

pcid/src/pci/bar.rs

@@ -2,6 +2,8 @@ use std::convert::TryInto;
 
 use serde::{Deserialize, Serialize};
 
+// This type is used instead of [pci_types::Bar] in the driver interface as the
+// latter can't be serialized and is missing the convenience functions of [PciBar].
 #[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize)]
 pub enum PciBar {
     None,

pcid/src/pci_header.rs

@@ -199,7 +199,6 @@ impl PciEndpointHeader {
     }
 
     /// Return the Headers BARs.
-    // FIXME use pci_types::Bar instead
     pub fn bars(&self, access: &impl ConfigRegionAccess) -> [PciBar; 6] {
         let endpoint_header = self.endpoint_header(access);