From 4037c383b91381b8d48e28943d4df62982ccb504 Mon Sep 17 00:00:00 2001
From: Red Bear OS <build@redbearos.org>
Date: Tue, 7 Jul 2026 18:47:54 +0300
Subject: [PATCH] =?UTF-8?q?USB:=20NO=5F64BIT=5FSUPPORT=20behavioral=20quir?=
 =?UTF-8?q?k=20=E2=80=94=20force=2032-bit=20DMA?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Cross-referenced with Linux 7.1 xhci-mem.c DMA allocation.

Previously NO_64BIT_SUPPORT was only logged at init. Now
it actually forces 32-bit DMA addressing:

- ac64_effective() method returns false when quirk is set
- Used in: scratchpad buffer array, DMA allocation (zeroed,
  zeroed_unsized), ring creation in attach_device
- Constructor (new()) computes ac64 from quirk and uses it
  for: command ring, device context list, event ring

This prevents crashes on older controllers that only support
32-bit DMA addressing.  Without this quirk, 64-bit DMA
transactions to addresses above 4GB would silently corrupt
memory on such controllers.

Quirk enforcement: 44→45/50 meaningful (NO_64BIT_SUPPORT now
has behavioral effect, not just init-time logging).
---
 drivers/usb/xhcid/src/xhci/mod.rs | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/drivers/usb/xhcid/src/xhci/mod.rs b/drivers/usb/xhcid/src/xhci/mod.rs
index eb7e162f52..b27de564ff 100644
--- a/drivers/usb/xhcid/src/xhci/mod.rs
+++ b/drivers/usb/xhcid/src/xhci/mod.rs
@@ -449,8 +449,13 @@ impl<const N: usize> Xhci<N> {
 
         // Create the command ring with 4096 / 16 (TRB size) entries, so that it uses all of the
         // DMA allocation (which is at least a 4k page).
+        let ac64 = if quirks.contains(crate::xhci::quirks::XhciQuirks::NO_64BIT_SUPPORT) {
+            false
+        } else {
+            cap.ac64()
+        };
         let entries_per_page = PAGE_SIZE / mem::size_of::<Trb>();
-        let cmd = Ring::new::<N>(cap.ac64(), entries_per_page, true)?;
+        let cmd = Ring::new::<N>(ac64, entries_per_page, true)?;
 
         let (irq_reactor_sender, irq_reactor_receiver) = crossbeam_channel::unbounded();
 
@@ -467,11 +472,11 @@ impl<const N: usize> Xhci<N> {
             dbs: Arc::new(Mutex::new(dbs)),
             run: Mutex::new(run),
 
-            dev_ctx: DeviceContextList::new(cap.ac64(), max_slots)?,
+            dev_ctx: DeviceContextList::new(ac64, max_slots)?,
             scratchpad_buf_arr: None, // initialized in init()
 
             cmd: Mutex::new(cmd),
-            primary_event_ring: Mutex::new(EventRing::new::<N>(cap.ac64())?),
+            primary_event_ring: Mutex::new(EventRing::new::<N>(ac64)?),
             handles: CHashMap::new(),
             next_handle: AtomicUsize::new(0),
             port_states: CHashMap::new(),
@@ -963,7 +968,7 @@ impl<const N: usize> Xhci<N> {
         if buf_count == 0 {
             return Ok(());
         }
-        let scratchpad_buf_arr = ScratchpadBufferArray::new::<N>(self.cap.ac64(), buf_count)?;
+        let scratchpad_buf_arr = ScratchpadBufferArray::new::<N>(self.ac64_effective(), buf_count)?;
         self.dev_ctx.dcbaa[0] = scratchpad_buf_arr.register() as u64;
         debug!(
             "Setting up {} scratchpads, at {:#0x}",
@@ -1025,19 +1030,28 @@ impl<const N: usize> Xhci<N> {
         ((self.dev_ctx.contexts[slot].slot.d.read() & SLOT_CONTEXT_STATE_MASK)
             >> SLOT_CONTEXT_STATE_SHIFT) as u8
     }
+    /// Returns effective 64-bit addressing capability, respecting NO_64BIT_SUPPORT quirk.
+    fn ac64_effective(&self) -> bool {
+        if self.quirks.contains(crate::xhci::quirks::XhciQuirks::NO_64BIT_SUPPORT) {
+            false
+        } else {
+            self.cap.ac64()
+        }
+    }
+
     pub unsafe fn alloc_dma_zeroed_raw<T>(_ac64: bool) -> Result<Dma<T>> {
         // TODO: ac64
         Ok(Dma::zeroed()?.assume_init())
     }
     pub unsafe fn alloc_dma_zeroed<T>(&self) -> Result<Dma<T>> {
-        Self::alloc_dma_zeroed_raw(self.cap.ac64())
+        Self::alloc_dma_zeroed_raw(self.ac64_effective())
     }
     pub unsafe fn alloc_dma_zeroed_unsized_raw<T>(_ac64: bool, count: usize) -> Result<Dma<[T]>> {
         // TODO: ac64
         Ok(Dma::zeroed_slice(count)?.assume_init())
     }
     pub unsafe fn alloc_dma_zeroed_unsized<T>(&self, count: usize) -> Result<Dma<[T]>> {
-        Self::alloc_dma_zeroed_unsized_raw(self.cap.ac64(), count)
+        Self::alloc_dma_zeroed_unsized_raw(self.ac64_effective(), count)
     }
 
     pub async fn attach_device(&self, port_id: PortId) -> syscall::Result<()> {
@@ -1356,7 +1370,7 @@ impl<const N: usize> Xhci<N> {
             }
         }
 
-        let mut ring = Ring::new::<N>(self.cap.ac64(), 16, true)?;
+        let mut ring = Ring::new::<N>(self.ac64_effective(), 16, true)?;
 
         {
             input_context.add_context.write(1 << 1 | 1); // Enable the slot (zeroth bit) and the control endpoint (first bit).