From ab7b9b735583d6e7145167978d480e1083ab0685 Mon Sep 17 00:00:00 2001
From: Thales Fragoso <thales.fragosoz@gmail.com>
Date: Thu, 20 Aug 2020 21:48:41 -0300
Subject: [PATCH] Make the creation of TxRingEntry and RxRingEntry const

---
 src/desc.rs | 10 +++++++---
 src/lib.rs  |  8 ++++----
 src/ring.rs | 26 +++++++++++++++++++++-----
 src/rx.rs   | 17 ++++++++++++-----
 src/tx.rs   | 18 +++++++++++++-----
 5 files changed, 57 insertions(+), 22 deletions(-)

diff --git a/src/desc.rs b/src/desc.rs
index fef0c2ae..56c3ca97 100644
--- a/src/desc.rs
+++ b/src/desc.rs
@@ -18,13 +18,17 @@ impl Clone for Descriptor {
 
 impl Default for Descriptor {
     fn default() -> Self {
-        Descriptor {
-            desc: Aligned([0; 4]),
-        }
+        Self::new()
     }
 }
 
 impl Descriptor {
+    pub const fn new() -> Self {
+        Self {
+            desc: Aligned([0; 4]),
+        }
+    }
+
     fn r(&self, n: usize) -> &RO<u32> {
         let ro = &self.desc.deref()[n] as *const _ as *const RO<u32>;
         unsafe { &*ro }
diff --git a/src/lib.rs b/src/lib.rs
index 21858769..f16fd287 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -24,11 +24,11 @@ mod smi;
 pub use ring::RingEntry;
 mod desc;
 mod rx;
-pub use rx::{RxDescriptor, RxError};
-use rx::{RxPacket, RxRing, RxRingEntry};
+pub use rx::{RxDescriptor, RxError, RxRingEntry};
+use rx::{RxPacket, RxRing};
 mod tx;
-pub use tx::{TxDescriptor, TxError};
-use tx::{TxRing, TxRingEntry};
+use tx::TxRing;
+pub use tx::{TxDescriptor, TxError, TxRingEntry};
 pub mod setup;
 pub use setup::EthPins;
 use setup::{
diff --git a/src/ring.rs b/src/ring.rs
index 9062e439..5850da4e 100644
--- a/src/ring.rs
+++ b/src/ring.rs
@@ -1,7 +1,7 @@
 use aligned::{Aligned, A8};
 use core::ops::{Deref, DerefMut};
 
-use crate::MTU;
+use crate::{RxDescriptor, TxDescriptor, MTU};
 
 pub trait RingDescriptor {
     fn setup(&mut self, buffer: *const u8, len: usize, next: Option<&Self>);
@@ -23,18 +23,34 @@ impl<T: Clone + RingDescriptor> Clone for RingEntry<T> {
 
 impl<T: Clone + RingDescriptor + Default> Default for RingEntry<T> {
     fn default() -> Self {
-        Self::new()
+        RingEntry {
+            desc: Aligned([T::default()]),
+            buffer: Aligned([0; MTU]),
+        }
     }
 }
 
-impl<T: Clone + RingDescriptor + Default> RingEntry<T> {
-    pub fn new() -> Self {
+impl RingEntry<TxDescriptor> {
+    /// Creates a RingEntry with a TxDescriptor.
+    pub const fn new() -> Self {
         RingEntry {
-            desc: Aligned([T::default()]),
+            desc: Aligned([TxDescriptor::new()]),
+            buffer: Aligned([0; MTU]),
+        }
+    }
+}
+
+impl RingEntry<RxDescriptor> {
+    /// Creates a RingEntry with a RxDescriptor.
+    pub const fn new() -> Self {
+        RingEntry {
+            desc: Aligned([RxDescriptor::new()]),
             buffer: Aligned([0; MTU]),
         }
     }
+}
 
+impl<T: Clone + RingDescriptor> RingEntry<T> {
     pub(crate) fn setup(&mut self, next: Option<&Self>) {
         let buffer = self.buffer.as_ptr();
         let len = self.buffer.len();
diff --git a/src/rx.rs b/src/rx.rs
index 4264f809..a98cabc0 100644
--- a/src/rx.rs
+++ b/src/rx.rs
@@ -50,15 +50,18 @@ pub struct RxDescriptor {
 
 impl Default for RxDescriptor {
     fn default() -> Self {
-        let mut desc = Descriptor::default();
-        unsafe {
-            desc.write(1, RXDESC_1_RCH);
-        }
-        RxDescriptor { desc }
+        Self::new()
     }
 }
 
 impl RxDescriptor {
+    /// Creates an zeroed RxDescriptor.
+    pub const fn new() -> Self {
+        Self {
+            desc: Descriptor::new(),
+        }
+    }
+
     /// Is owned by the DMA engine?
     fn is_owned(&self) -> bool {
         (self.desc.read(0) & RXDESC_0_OWN) == RXDESC_0_OWN
@@ -126,6 +129,10 @@ pub type RxRingEntry = RingEntry<RxDescriptor>;
 
 impl RingDescriptor for RxDescriptor {
     fn setup(&mut self, buffer: *const u8, len: usize, next: Option<&Self>) {
+        // Defer this initialization to this function, so we can have `RingEntry` on bss.
+        unsafe {
+            self.desc.write(1, RXDESC_1_RCH);
+        }
         self.set_buffer1(buffer, len);
         match next {
             Some(next) => self.set_buffer2(&next.desc as *const Descriptor as *const u8),
diff --git a/src/tx.rs b/src/tx.rs
index ad79ec46..a72aa7a2 100644
--- a/src/tx.rs
+++ b/src/tx.rs
@@ -47,15 +47,18 @@ pub struct TxDescriptor {
 
 impl Default for TxDescriptor {
     fn default() -> Self {
-        let mut desc = Descriptor::default();
-        unsafe {
-            desc.write(0, TXDESC_0_TCH | TXDESC_0_IC | TXDESC_0_FS | TXDESC_0_LS);
-        }
-        TxDescriptor { desc }
+        Self::new()
     }
 }
 
 impl TxDescriptor {
+    /// Creates an zeroed TxDescriptor.
+    pub const fn new() -> Self {
+        Self {
+            desc: Descriptor::new(),
+        }
+    }
+
     /// Is owned by the DMA engine?
     fn is_owned(&self) -> bool {
         (self.desc.read(0) & TXDESC_0_OWN) == TXDESC_0_OWN
@@ -115,6 +118,11 @@ pub type TxRingEntry = RingEntry<TxDescriptor>;
 
 impl RingDescriptor for TxDescriptor {
     fn setup(&mut self, buffer: *const u8, _len: usize, next: Option<&Self>) {
+        // Defer this initialization to this function, so we can have `RingEntry` on bss.
+        unsafe {
+            self.desc
+                .write(0, TXDESC_0_TCH | TXDESC_0_IC | TXDESC_0_FS | TXDESC_0_LS);
+        }
         self.set_buffer1(buffer);
         match next {
             Some(next) => self.set_buffer2(&next.desc as *const Descriptor as *const u8),