feat: ✨ Switch mailboxes to correct DMA-backed storage by default

Allocate DmaBackedMailboxStorage out of DMA_ALLOCATOR.
Replace DMA bump_allocator with buddy_alloc.

Cargo.lock

@@ -67,6 +67,11 @@ version = "1.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
 
+[[package]]
+name = "buddy-alloc"
+version = "0.5.0"
+source = "git+https://github.com/metta-systems/buddy-alloc?branch=feature/allocator-api#70c17c858100282252754981f13e9442b86e07e0"
+
 [[package]]
 name = "bytes"
 version = "1.1.0"
@@ -385,8 +390,10 @@ version = "0.0.1"
 dependencies = [
  "bit_field",
  "bitflags",
+ "buddy-alloc",
  "cfg-if",
  "cortex-a",
+ "once_cell",
  "qemu-exit",
  "r0",
  "snafu",

machine/Cargo.toml

@@ -38,3 +38,5 @@ bit_field = "0.10"
 bitflags = "1.3"
 cfg-if = "1.0"
 snafu = { version = "0.7", default-features = false }
+buddy-alloc = { git = "https://github.com/metta-systems/buddy-alloc", version = "0.5.0", branch = "feature/allocator-api" }
+once_cell = { version = "1.10.0", default-features = false, features = ["unstable"] }

machine/src/lib.rs

@@ -5,6 +5,7 @@
 #![feature(format_args_nl)]
 #![feature(core_intrinsics)]
 #![feature(stmt_expr_attributes)]
+#![feature(slice_ptr_get)]
 #![feature(nonnull_slice_from_raw_parts)]
 #![feature(custom_test_frameworks)]
 #![test_runner(crate::tests::test_runner)]
@@ -18,6 +19,12 @@
 #[cfg(not(target_arch = "aarch64"))]
 use architecture_not_supported_sorry;
 
+use {
+    buddy_alloc::{BuddyAlloc, BuddyAllocParam},
+    once_cell::unsync::Lazy,
+    platform::memory::map::virt::{DMA_HEAP_END, DMA_HEAP_START},
+};
+
 /// Architecture-specific code.
 #[macro_use]
 pub mod arch;
@@ -41,19 +48,20 @@ pub static CONSOLE: sync::NullLock<devices::Console> = sync::NullLock::new(devic
 /// The global allocator for DMA-able memory. That is, memory which is tagged
 /// non-cacheable in the page tables.
 #[allow(dead_code)]
-static DMA_ALLOCATOR: sync::NullLock<mm::BumpAllocator> =
-    sync::NullLock::new(mm::BumpAllocator::new(
-        // @todo Init this after we loaded boot memory map
-        platform::memory::map::virt::DMA_HEAP_START as usize,
-        platform::memory::map::virt::DMA_HEAP_END as usize,
-        "Global DMA Allocator",
-        // Try the following arguments instead to see all mailbox operations
-        // fail. It will cause the allocator to use memory that are marked
-        // cacheable and therefore not DMA-safe. The answer from the VideoCore
-        // won't be received by the CPU because it reads an old cached value
-        // that resembles an error case instead.
+static DMA_ALLOCATOR: sync::NullLock<Lazy<BuddyAlloc>> =
+    sync::NullLock::new(Lazy::new(|| unsafe {
+        BuddyAlloc::new(BuddyAllocParam::new(
+            // @todo Init this after we loaded boot memory map
+            DMA_HEAP_START as *const u8,
+            DMA_HEAP_END - DMA_HEAP_START,
+            64,
+        ))
+    }));
+// Try the following arguments instead to see all mailbox operations
+// fail. It will cause the allocator to use memory that are marked
+// cacheable and therefore not DMA-safe. The answer from the VideoCore
+// won't be received by the CPU because it reads an old cached value
+// that resembles an error case instead.
 
-        // 0x00600000 as usize,
-        // 0x007FFFFF as usize,
-        // "Global Non-DMA Allocator",
-    ));
+// 0x00600000 as usize,
+// 0x007FFFFF as usize,

machine/src/platform/rpi3/mailbox.rs

@@ -13,8 +13,11 @@
 
 use {
     super::BcmHost,
-    crate::{platform::MMIODerefWrapper, println},
+    crate::{platform::MMIODerefWrapper, println, DMA_ALLOCATOR},
     core::{
+        alloc::{AllocError, Allocator, Layout},
+        mem,
+        ptr::NonNull,
         result::Result as CoreResult,
         sync::atomic::{compiler_fence, Ordering},
     },
@@ -31,14 +34,14 @@ use {
 /// The address for the buffer needs to be 16-byte aligned
 /// so that the VideoCore can handle it properly.
 /// The reason is that lowest 4 bits of the address will contain the channel number.
-pub struct Mailbox<const N_SLOTS: usize, Storage = LocalMailboxStorage<N_SLOTS>> {
+pub struct Mailbox<const N_SLOTS: usize, Storage = DmaBackedMailboxStorage<N_SLOTS>> {
     registers: Registers,
     pub buffer: Storage,
 }
 
 /// Mailbox that is ready to be called.
 /// This prevents invalid use of the mailbox until it is fully prepared.
-pub struct PreparedMailbox<const N_SLOTS: usize, Storage = LocalMailboxStorage<N_SLOTS>>(
+pub struct PreparedMailbox<const N_SLOTS: usize, Storage = DmaBackedMailboxStorage<N_SLOTS>>(
     Mailbox<N_SLOTS, Storage>,
 );
 
@@ -96,6 +99,8 @@ pub enum MailboxError {
     Unknown,
     #[snafu(display("Timeout"))]
     Timeout,
+    #[snafu(display("AllocError"))]
+    Alloc,
 }
 
 pub type Result<T> = CoreResult<T, MailboxError>;
@@ -111,7 +116,9 @@ pub trait MailboxOps {
 }
 
 pub trait MailboxStorage {
-    fn new() -> Self;
+    fn new() -> Result<Self>
+    where
+        Self: Sized;
 }
 
 pub trait MailboxStorageRef {
@@ -127,11 +134,45 @@ pub struct LocalMailboxStorage<const N_SLOTS: usize> {
     pub storage: [u32; N_SLOTS],
 }
 
+pub struct DmaBackedMailboxStorage<const N_SLOTS: usize> {
+    pub storage: *mut u32,
+}
+
 impl<const N_SLOTS: usize> MailboxStorage for LocalMailboxStorage<N_SLOTS> {
-    fn new() -> Self {
-        Self {
+    fn new() -> Result<Self> {
+        Ok(Self {
             storage: [0u32; N_SLOTS],
-        }
+        })
+    }
+}
+
+impl<const N_SLOTS: usize> MailboxStorage for DmaBackedMailboxStorage<N_SLOTS> {
+    fn new() -> Result<Self> {
+        Ok(Self {
+            storage: DMA_ALLOCATOR
+                .lock(|a| {
+                    a.allocate(
+                        Layout::from_size_align(N_SLOTS * mem::size_of::<u32>(), 16)
+                            .map_err(|_| AllocError)?,
+                    )
+                })
+                .map_err(|_| MailboxError::Alloc)?
+                .as_mut_ptr() as *mut u32,
+        })
+    }
+}
+
+impl<const N_SLOTS: usize> Drop for DmaBackedMailboxStorage<N_SLOTS> {
+    fn drop(&mut self) {
+        DMA_ALLOCATOR
+            .lock::<_, Result<()>>(|a| unsafe {
+                Ok(a.deallocate(
+                    NonNull::new_unchecked(self.storage as *mut u8),
+                    Layout::from_size_align(N_SLOTS * mem::size_of::<u32>(), 16)
+                        .map_err(|_| MailboxError::Alloc)?,
+                ))
+            })
+            .unwrap_or(())
     }
 }
 
@@ -154,6 +195,25 @@ impl<const N_SLOTS: usize> MailboxStorageRef for LocalMailboxStorage<N_SLOTS> {
     }
 }
 
+impl<const N_SLOTS: usize> MailboxStorageRef for DmaBackedMailboxStorage<N_SLOTS> {
+    fn as_ref(&self) -> &[u32] {
+        unsafe { core::slice::from_raw_parts(self.storage.cast(), N_SLOTS) }
+    }
+
+    fn as_mut(&mut self) -> &mut [u32] {
+        unsafe { core::slice::from_raw_parts_mut(self.storage.cast(), N_SLOTS) }
+    }
+
+    fn as_ptr(&self) -> *const u32 {
+        self.storage.cast()
+    }
+
+    // @todo Probably need a ResultMailbox for accessing data after call()?
+    fn value_at(&self, index: usize) -> u32 {
+        self.as_ref()[index]
+    }
+}
+
 /*
  * Source https://elinux.org/RPi_Framebuffer
  * Source for channels 8 and 9: https://github.com/raspberrypi/firmware/wiki/Mailboxes
@@ -315,7 +375,7 @@ impl<const N_SLOTS: usize, Storage: MailboxStorage + MailboxStorageRef> Mailbox<
     pub unsafe fn new(base_addr: usize) -> Result<Mailbox<N_SLOTS, Storage>> {
         Ok(Mailbox {
             registers: Registers::new(base_addr),
-            buffer: Storage::new(),
+            buffer: Storage::new()?,
         })
     }