Add support for printing DTS out of FDT

src/fdt/mod.rs

@@ -20,7 +20,7 @@ mod node;
 mod property;
 use core::ffi::CStr;
 use core::mem::offset_of;
-use core::ptr;
+use core::{fmt, ptr};
 
 pub use node::FdtNode;
 pub use property::FdtProperty;
@@ -491,6 +491,15 @@ impl<'a> Fdt<'a> {
     }
 }
 
+impl fmt::Display for Fdt<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        writeln!(f, "/dts-v1/;")?;
+        writeln!(f)?;
+        let root = self.root().map_err(|_| fmt::Error)?;
+        root.fmt_recursive(f, 0)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/fdt/node.rs

@@ -8,6 +8,8 @@
 
 //! A read-only API for inspecting a device tree node.
 
+use core::fmt;
+
 use super::{FDT_TAGSIZE, Fdt, FdtToken};
 use crate::error::FdtError;
 use crate::fdt::property::{FdtPropIter, FdtProperty};
@@ -149,6 +151,43 @@ impl<'a> FdtNode<'a> {
             offset: self.offset,
         }
     }
+
+    pub(crate) fn fmt_recursive(&self, f: &mut fmt::Formatter<'_>, indent: usize) -> fmt::Result {
+        let name = self.name().map_err(|_| fmt::Error)?;
+        if name.is_empty() {
+            writeln!(f, "{:indent$}/ {{", "", indent = indent)?;
+        } else {
+            writeln!(f, "{:indent$}{} {{", "", name, indent = indent)?;
+        }
+
+        let mut has_properties = false;
+        for prop in self.properties() {
+            has_properties = true;
+            match prop {
+                Ok(prop) => prop.fmt(f, indent + 4)?,
+                Err(_e) => {
+                    writeln!(f, "<Error reading property>")?;
+                }
+            }
+        }
+
+        let mut first_child = true;
+        for child in self.children() {
+            if !first_child || has_properties {
+                writeln!(f)?;
+            }
+
+            first_child = false;
+            match child {
+                Ok(child) => child.fmt_recursive(f, indent + 4)?,
+                Err(_e) => {
+                    writeln!(f, "<Error reading child node>")?;
+                }
+            }
+        }
+
+        writeln!(f, "{:indent$}}};", "", indent = indent)
+    }
 }
 
 /// An iterator over the children of a device tree node.

src/fdt/property.rs

@@ -9,6 +9,7 @@
 //! A read-only API for inspecting a device tree property.
 
 use core::ffi::CStr;
+use core::fmt;
 
 use zerocopy::{FromBytes, big_endian};
 
@@ -125,6 +126,59 @@ impl<'a> FdtProperty<'a> {
     pub fn as_str_list(&self) -> impl Iterator<Item = &'a str> {
         FdtStringListIterator { value: self.value }
     }
+
+    pub(crate) fn fmt(&self, f: &mut fmt::Formatter<'_>, indent: usize) -> fmt::Result {
+        write!(f, "{:indent$}{}", "", self.name, indent = indent)?;
+
+        if self.value.is_empty() {
+            writeln!(f, ";")?;
+            return Ok(());
+        }
+
+        let is_printable = self
+            .value
+            .iter()
+            .all(|&ch| ch.is_ascii_graphic() || ch == b' ' || ch == 0);
+        let has_empty = self.value.windows(2).any(|window| window == [0, 0]);
+        if is_printable && self.value.ends_with(&[0]) && !has_empty {
+            let mut strings = self.as_str_list();
+            if let Some(first) = strings.next() {
+                write!(f, " = \"{first}\"")?;
+                for s in strings {
+                    write!(f, ", \"{s}\"")?;
+                }
+                writeln!(f, ";")?;
+                return Ok(());
+            }
+        }
+
+        if self.value.len().is_multiple_of(4) {
+            write!(f, " = <")?;
+            for (i, chunk) in self.value.chunks_exact(4).enumerate() {
+                if i > 0 {
+                    write!(f, " ")?;
+                }
+                let val = u32::from_be_bytes(
+                    chunk
+                        .try_into()
+                        .expect("u32::from_be_bytes() should always succeed with 4 bytes"),
+                );
+                write!(f, "0x{val:02x}")?;
+            }
+            writeln!(f, ">;")?;
+        } else {
+            write!(f, " = [")?;
+            for (i, byte) in self.value.iter().enumerate() {
+                if i > 0 {
+                    write!(f, " ")?;
+                }
+                write!(f, "{byte:02x}")?;
+            }
+            writeln!(f, "];")?;
+        }
+
+        Ok(())
+    }
 }
 
 /// An iterator over the properties of a device tree node.

tests/dts/test_pretty_print.dts

@@ -0,0 +1,27 @@
+/dts-v1/;
+
+/ {
+    #address-cells = <0x01>;
+    #size-cells = <0x01>;
+    compatible = "acme,coyote";
+    model = "ACME Coyote";
+    phandle = <0x01>;
+    str-list = "first", "second";
+    empty-prop;
+    byte-array = [01 23 45 67 89 ab cd];
+
+    cpus {
+        #address-cells = <0x01>;
+        #size-cells = <0x00>;
+
+        cpu@0 {
+            compatible = "arm,cortex-a9";
+            reg = <0x00>;
+        };
+    };
+
+    memory@80000000 {
+        device_type = "memory";
+        reg = <0x80000000 0x20000000>;
+    };
+};

tests/fdt.rs

@@ -140,3 +140,14 @@ fn find_node_by_path() {
     assert!(fdt.find_node("/x").is_none());
     assert!(fdt.find_node("").is_none());
 }
+
+#[test]
+fn pretty_print() {
+    let dtb = include_bytes!("dtb/test_pretty_print.dtb");
+    let fdt = Fdt::new(dtb).unwrap();
+    let s = fdt.to_string();
+    let expected = include_str!("dts/test_pretty_print.dts")
+        // account for Windows newlines, if needed
+        .replace("\r\n", "\n");
+    assert_eq!(s, expected);
+}