Merge #1247

1247: `PacketQueue::init()` r=davidedellagiustina a=davidedellagiustina

`PacketQueue` is pretty big, so I added a method to initialize it without requiring an allocation on the stack (which could in fact overflow). Before this PR, the only solution would be to declare a `PacketQueue` instance as a `static mut`, while now one could for example have a `Box<MaybeUninit<PacketQueue<...>>>` and then use `init()` on it.

Ideally, the same work would need to be done for all those structures that own big arrays which could overflow the stack.

Co-authored-by: Davide Della Giustina <davide@dellagiustina.com>

embassy-stm32/src/eth/mod.rs

@@ -5,6 +5,7 @@
 mod _version;
 pub mod generic_smi;
 
+use core::mem::MaybeUninit;
 use core::task::Context;
 
 use embassy_net_driver::{Capabilities, LinkState};
@@ -39,6 +40,13 @@ impl<const TX: usize, const RX: usize> PacketQueue<TX, RX> {
             rx_buf: [Packet([0; RX_BUFFER_SIZE]); RX],
         }
     }
+
+    // Allow to initialize a Self without requiring it to go on the stack
+    pub fn init(this: &mut MaybeUninit<Self>) {
+        unsafe {
+            this.as_mut_ptr().write_bytes(0u8, core::mem::size_of::<Self>());
+        }
+    }
 }
 
 static WAKER: AtomicWaker = AtomicWaker::new();