Kernel/USB: Add support for async & interrupt transfers

Add support for async transfers by using a separate kernel task to poll
a list of active async transfers on a set time interval, and invoke
their user-provided callback function when they are complete. Also add
support for the interrupt class of transfers, building off of this async
functionality.

8 files changed, 181 insertions, 62 deletions

diff --git a/Kernel/Bus/USB/UHCI/UHCIController.cpp b/Kernel/Bus/USB/UHCI/UHCIController.cpp
index bb425e4743..17e0df4344 100644
--- a/Kernel/Bus/USB/UHCI/UHCIController.cpp
+++ b/Kernel/Bus/USB/UHCI/UHCIController.cpp
@@ -5,6 +5,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/Find.h>
 #include <AK/Platform.h>
 #include <Kernel/Arch/Delay.h>
 #include <Kernel/Bus/PCI/API.h>
@@ -78,6 +79,7 @@ ErrorOr<void> UHCIController::initialize()
     dmesgln("UHCI: I/O base {}", m_registers_io_window);
     dmesgln("UHCI: Interrupt line: {}", interrupt_number());
 
+    TRY(spawn_async_poll_process());
     TRY(spawn_port_process());
 
     TRY(reset());
@@ -88,6 +90,7 @@ UNMAP_AFTER_INIT UHCIController::UHCIController(PCI::DeviceIdentifier const& pci
     : PCI::Device(pci_device_identifier.address())
     , IRQHandler(pci_device_identifier.interrupt_line().value())
     , m_registers_io_window(move(registers_io_window))
+    , m_async_lock(LockRank::None)
     , m_schedule_lock(LockRank::None)
 {
 }
@@ -132,14 +135,11 @@ UNMAP_AFTER_INIT ErrorOr<void> UHCIController::create_structures()
 {
     m_queue_head_pool = TRY(UHCIDescriptorPool<QueueHead>::try_create("Queue Head Pool"sv));
 
-    // Used as a sentinel value to loop back to the beginning of the list
+    // Doesn't do anything other than give interrupt transfer queues something to set as prev QH so that we don't have to handle that as an extra edge case
     m_schedule_begin_anchor = allocate_queue_head();
-    // Each interrupt QH anchor in the array is linked into the schedule so that
-    // it is executed once every (2^i) milliseconds, where i is it's index
-    for (int i = 0; i < NUMBER_OF_INTERRUPT_QHS; i++) {
-        m_interrupt_qh_anchor_arr[i] = allocate_queue_head();
-    }
-    // Create the Full Speed, Low Speed Control and Bulk Queue Heads
+
+    // Create the Interrupt, Full Speed, Low Speed Control and Bulk Queue Heads
+    m_interrupt_qh_anchor = allocate_queue_head();
     m_ls_control_qh_anchor = allocate_queue_head();
     m_fs_control_qh_anchor = allocate_queue_head();
     m_bulk_qh_anchor = allocate_queue_head();
@@ -201,15 +201,11 @@ UNMAP_AFTER_INIT void UHCIController::setup_schedule()
     // Not specified in the datasheet, however, is another Queue Head with an "inactive" Transfer Descriptor. This
     // is to circumvent a bug in the silicon of the PIIX4's UHCI controller.
     // https://github.com/openbsd/src/blob/master/sys/dev/usb/uhci.c#L390
-    m_schedule_begin_anchor->link_next_queue_head(m_interrupt_qh_anchor_arr[0]);
+    m_schedule_begin_anchor->link_next_queue_head(m_interrupt_qh_anchor);
     m_schedule_begin_anchor->terminate_element_link_ptr();
 
-    for (int i = 0; i < NUMBER_OF_INTERRUPT_QHS - 1; i++) {
-        m_interrupt_qh_anchor_arr[i]->link_next_queue_head(m_interrupt_qh_anchor_arr[i + 1]);
-        m_interrupt_qh_anchor_arr[i]->terminate_element_link_ptr();
-    }
-    m_interrupt_qh_anchor_arr[NUMBER_OF_INTERRUPT_QHS - 1]->link_next_queue_head(m_ls_control_qh_anchor);
-    m_interrupt_qh_anchor_arr[NUMBER_OF_INTERRUPT_QHS - 1]->terminate_element_link_ptr();
+    m_interrupt_qh_anchor->link_next_queue_head(m_ls_control_qh_anchor);
+    m_interrupt_qh_anchor->terminate_element_link_ptr();
 
     m_ls_control_qh_anchor->link_next_queue_head(m_fs_control_qh_anchor);
     m_ls_control_qh_anchor->terminate_element_link_ptr();
@@ -227,20 +223,12 @@ UNMAP_AFTER_INIT void UHCIController::setup_schedule()
 
     u32* framelist = reinterpret_cast<u32*>(m_framelist->vaddr().as_ptr());
     for (int frame_num = 0; frame_num < UHCI_NUMBER_OF_FRAMES; frame_num++) {
-        auto frame_iso_td = m_iso_td_list.at(frame_num % UHCI_NUMBER_OF_ISOCHRONOUS_TDS);
-        // Each frame pointer points to iso_td % NUM_ISO_TDS
-        for (int i = NUMBER_OF_INTERRUPT_QHS - 1; i >= 0; i--) {
-            if (frame_num % (1 << i) == 0) {
-                frame_iso_td->link_queue_head(m_interrupt_qh_anchor_arr[i]->paddr());
-                break;
-            }
-        }
+        auto& frame_iso_td = m_iso_td_list.at(frame_num % UHCI_NUMBER_OF_ISOCHRONOUS_TDS);
+        frame_iso_td->link_queue_head(m_schedule_begin_anchor->paddr());
         framelist[frame_num] = frame_iso_td->paddr();
     }
 
-    for (int i = 0; i < NUMBER_OF_INTERRUPT_QHS; i++) {
-        m_interrupt_qh_anchor_arr[i]->print();
-    }
+    m_interrupt_qh_anchor->print();
     m_ls_control_qh_anchor->print();
     m_fs_control_qh_anchor->print();
     m_bulk_qh_anchor->print();
@@ -387,6 +375,70 @@ void UHCIController::dequeue_qh(QueueHead* transfer_queue)
     transfer_queue->prev_qh()->link_next_queue_head(transfer_queue->next_qh());
 }
 
+ErrorOr<QueueHead*> UHCIController::create_transfer_queue(Transfer& transfer)
+{
+    Pipe& pipe = transfer.pipe();
+
+    // Create a new descriptor chain
+    TransferDescriptor* last_data_descriptor;
+    TransferDescriptor* data_descriptor_chain;
+    auto buffer_address = Ptr32<u8>(transfer.buffer_physical().as_ptr());
+    TRY(create_chain(pipe, transfer.pipe().direction() == Pipe::Direction::In ? PacketID::IN : PacketID::OUT, buffer_address, pipe.max_packet_size(), transfer.transfer_data_size(), &data_descriptor_chain, &last_data_descriptor));
+
+    last_data_descriptor->terminate();
+
+    if constexpr (UHCI_VERBOSE_DEBUG) {
+        if (data_descriptor_chain) {
+            dbgln("Data TD");
+            data_descriptor_chain->print();
+        }
+    }
+
+    QueueHead* transfer_queue = allocate_queue_head();
+    if (!transfer_queue) {
+        free_descriptor_chain(data_descriptor_chain);
+        return ENOMEM;
+    }
+
+    transfer_queue->attach_transfer_descriptor_chain(data_descriptor_chain);
+    transfer_queue->set_transfer(&transfer);
+
+    return transfer_queue;
+}
+
+ErrorOr<void> UHCIController::submit_async_transfer(NonnullOwnPtr<AsyncTransferHandle> async_handle, QueueHead* anchor, QueueHead* transfer_queue)
+{
+    {
+        SpinlockLocker locker { m_async_lock };
+        auto iter = find_if(m_active_async_transfers.begin(), m_active_async_transfers.end(), [](auto& handle) { return handle == nullptr; });
+        if (iter == m_active_async_transfers.end())
+            return ENOMEM;
+        *iter = move(async_handle);
+    }
+
+    enqueue_qh(transfer_queue, anchor);
+
+    return {};
+}
+
+void UHCIController::cancel_async_transfer(NonnullLockRefPtr<Transfer> transfer)
+{
+    SpinlockLocker locker { m_async_lock };
+
+    auto iter = find_if(m_active_async_transfers.begin(), m_active_async_transfers.end(), [transfer](auto& handle) { return handle != nullptr && handle->transfer.ptr() == transfer.ptr(); });
+    if (iter == m_active_async_transfers.end()) {
+        dbgln("Error: couldn't cancel supplied async transfer");
+        return; // We can't really do anything here, so just give up
+    }
+
+    auto& transfer_queue = (*iter)->qh;
+    dequeue_qh(transfer_queue);
+    free_descriptor_chain(transfer_queue->get_first_td());
+    transfer_queue->free();
+    m_queue_head_pool->release_to_pool(transfer_queue);
+    *iter = nullptr;
+}
+
 ErrorOr<size_t> UHCIController::submit_control_transfer(Transfer& transfer)
 {
     Pipe& pipe = transfer.pipe(); // Short circuit the pipe related to this transfer
@@ -467,35 +519,11 @@ ErrorOr<size_t> UHCIController::submit_control_transfer(Transfer& transfer)
 
 ErrorOr<size_t> UHCIController::submit_bulk_transfer(Transfer& transfer)
 {
-    Pipe& pipe = transfer.pipe();
-    dbgln_if(UHCI_DEBUG, "UHCI: Received bulk transfer for address {}. Root Hub is at address {}.", pipe.device_address(), m_root_hub->device_address());
-
-    // Create a new descriptor chain
-    TransferDescriptor* last_data_descriptor;
-    TransferDescriptor* data_descriptor_chain;
-    auto buffer_address = Ptr32<u8>(transfer.buffer_physical().as_ptr());
-    TRY(create_chain(pipe, transfer.pipe().direction() == Pipe::Direction::In ? PacketID::IN : PacketID::OUT, buffer_address, pipe.max_packet_size(), transfer.transfer_data_size(), &data_descriptor_chain, &last_data_descriptor));
-
-    last_data_descriptor->terminate();
-
-    if constexpr (UHCI_VERBOSE_DEBUG) {
-        if (data_descriptor_chain) {
-            dbgln("Data TD");
-            data_descriptor_chain->print();
-        }
-    }
-
-    QueueHead* transfer_queue = allocate_queue_head();
-    if (!transfer_queue) {
-        free_descriptor_chain(data_descriptor_chain);
-        return ENOMEM;
-    }
-
-    transfer_queue->attach_transfer_descriptor_chain(data_descriptor_chain);
-    transfer_queue->set_transfer(&transfer);
-
+    auto transfer_queue = TRY(create_transfer_queue(transfer));
     enqueue_qh(transfer_queue, m_bulk_qh_anchor);
 
+    dbgln_if(UHCI_DEBUG, "UHCI: Received bulk transfer for address {}. Root Hub is at address {}.", transfer.pipe().device_address(), m_root_hub->device_address());
+
     size_t transfer_size = 0;
     while (!transfer.complete()) {
         transfer_size = poll_transfer_queue(*transfer_queue);
@@ -510,6 +538,21 @@ ErrorOr<size_t> UHCIController::submit_bulk_transfer(Transfer& transfer)
     return transfer_size;
 }
 
+ErrorOr<void> UHCIController::submit_async_interrupt_transfer(NonnullLockRefPtr<Transfer> transfer, u16 ms_interval)
+{
+    dbgln_if(UHCI_DEBUG, "UHCI: Received interrupt transfer for address {}. Root Hub is at address {}.", transfer->pipe().device_address(), m_root_hub->device_address());
+
+    if (ms_interval == 0) {
+        return EINVAL;
+    }
+
+    auto transfer_queue = TRY(create_transfer_queue(*transfer));
+    auto async_transfer_handle = TRY(adopt_nonnull_own_or_enomem(new (nothrow) AsyncTransferHandle { transfer, transfer_queue, ms_interval }));
+    TRY(submit_async_transfer(move(async_transfer_handle), m_interrupt_qh_anchor, transfer_queue));
+
+    return {};
+}
+
 size_t UHCIController::poll_transfer_queue(QueueHead& transfer_queue)
 {
     Transfer* transfer = transfer_queue.transfer();
@@ -556,6 +599,33 @@ ErrorOr<void> UHCIController::spawn_port_process()
     return {};
 }
 
+ErrorOr<void> UHCIController::spawn_async_poll_process()
+{
+    LockRefPtr<Thread> async_poll_thread;
+    (void)Process::create_kernel_process(async_poll_thread, TRY(KString::try_create("UHCI Async Poll Task"sv)), [&] {
+        u16 poll_interval_ms = 1024;
+        for (;;) {
+            {
+                SpinlockLocker locker { m_async_lock };
+                for (OwnPtr<AsyncTransferHandle>& handle : m_active_async_transfers) {
+                    if (handle != nullptr) {
+                        poll_interval_ms = min(poll_interval_ms, handle->ms_poll_interval);
+                        QueueHead* qh = handle->qh;
+                        for (auto td = qh->get_first_td(); td != nullptr && !td->active(); td = td->next_td()) {
+                            if (td->next_td() == nullptr) { // Finished QH
+                                handle->transfer->invoke_async_callback();
+                                qh->reinitialize(); // Set the QH to be active again
+                            }
+                        }
+                    }
+                }
+            }
+            (void)Thread::current()->sleep(Time::from_milliseconds(poll_interval_ms));
+        }
+    });
+    return {};
+}
+
 bool UHCIController::handle_irq(RegisterState const&)
 {
     u32 status = read_usbsts();
diff --git a/Kernel/Bus/USB/UHCI/UHCIController.h b/Kernel/Bus/USB/UHCI/UHCIController.h
index 882e54bffd..ccbd218e6f 100644
--- a/Kernel/Bus/USB/UHCI/UHCIController.h
+++ b/Kernel/Bus/USB/UHCI/UHCIController.h
@@ -31,7 +31,6 @@ class UHCIController final
 
     static constexpr u8 MAXIMUM_NUMBER_OF_TDS = 128; // Upper pool limit. This consumes the second page we have allocated
     static constexpr u8 MAXIMUM_NUMBER_OF_QHS = 64;
-    static constexpr u8 NUMBER_OF_INTERRUPT_QHS = 11;
 
 public:
     static constexpr u8 NUMBER_OF_ROOT_PORTS = 2;
@@ -44,10 +43,16 @@ public:
     virtual ErrorOr<void> reset() override;
     virtual ErrorOr<void> stop() override;
     virtual ErrorOr<void> start() override;
+    ErrorOr<void> spawn_async_poll_process();
     ErrorOr<void> spawn_port_process();
 
+    ErrorOr<QueueHead*> create_transfer_queue(Transfer& transfer);
+    ErrorOr<void> submit_async_transfer(NonnullOwnPtr<AsyncTransferHandle> async_handle, QueueHead* anchor, QueueHead* transfer_queue);
+
+    virtual void cancel_async_transfer(NonnullLockRefPtr<Transfer> transfer) override;
     virtual ErrorOr<size_t> submit_control_transfer(Transfer& transfer) override;
     virtual ErrorOr<size_t> submit_bulk_transfer(Transfer& transfer) override;
+    virtual ErrorOr<void> submit_async_interrupt_transfer(NonnullLockRefPtr<Transfer> transfer, u16 ms_interval) override;
 
     void get_port_status(Badge<UHCIRootHub>, u8, HubStatus&);
     ErrorOr<void> set_port_feature(Badge<UHCIRootHub>, u8, HubFeatureSelector);
@@ -95,15 +100,17 @@ private:
 
     NonnullOwnPtr<IOWindow> m_registers_io_window;
 
+    Spinlock m_async_lock;
     Spinlock m_schedule_lock;
 
     OwnPtr<UHCIRootHub> m_root_hub;
     OwnPtr<UHCIDescriptorPool<QueueHead>> m_queue_head_pool;
     OwnPtr<UHCIDescriptorPool<TransferDescriptor>> m_transfer_descriptor_pool;
     Vector<TransferDescriptor*> m_iso_td_list;
+    Array<OwnPtr<AsyncTransferHandle>, MAXIMUM_NUMBER_OF_QHS> m_active_async_transfers;
 
     QueueHead* m_schedule_begin_anchor;
-    Array<QueueHead*, NUMBER_OF_INTERRUPT_QHS> m_interrupt_qh_anchor_arr;
+    QueueHead* m_interrupt_qh_anchor;
     QueueHead* m_ls_control_qh_anchor;
     QueueHead* m_fs_control_qh_anchor;
     // Always final queue in the schedule, may loop back to previous QH for bandwidth
diff --git a/Kernel/Bus/USB/UHCI/UHCIDescriptorTypes.h b/Kernel/Bus/USB/UHCI/UHCIDescriptorTypes.h
index 6375af1227..8dab52c99c 100644
--- a/Kernel/Bus/USB/UHCI/UHCIDescriptorTypes.h
+++ b/Kernel/Bus/USB/UHCI/UHCIDescriptorTypes.h
@@ -356,6 +356,15 @@ struct alignas(16) QueueHead {
         m_bookkeeping->in_use = false;
     }
 
+    void reinitialize()
+    {
+
+        for (TransferDescriptor* iter = get_first_td(); iter != nullptr; iter = iter->next_td()) {
+            iter->set_active();
+        }
+        attach_transfer_descriptor_chain(get_first_td());
+    }
+
 private:
     u32 m_link_ptr { 0 };                  // Pointer to the next horizontal object that the controller will execute after this one
     volatile u32 m_element_link_ptr { 0 }; // Pointer to the first data object in the queue (can be modified by hw)
@@ -366,4 +375,11 @@ private:
 };
 
 static_assert(AssertSize<QueueHead, 32>()); // Queue Head is always 8 Dwords
+
+struct AsyncTransferHandle {
+    NonnullLockRefPtr<Transfer> transfer;
+    QueueHead* qh;
+    u16 ms_poll_interval;
+};
+
 }
diff --git a/Kernel/Bus/USB/USBController.h b/Kernel/Bus/USB/USBController.h
index 47fc1d1d6d..73bb01d9c3 100644
--- a/Kernel/Bus/USB/USBController.h
+++ b/Kernel/Bus/USB/USBController.h
@@ -23,8 +23,10 @@ public:
     virtual ErrorOr<void> stop() = 0;
     virtual ErrorOr<void> start() = 0;
 
+    virtual void cancel_async_transfer(NonnullLockRefPtr<Transfer> transfer) = 0;
     virtual ErrorOr<size_t> submit_control_transfer(Transfer&) = 0;
     virtual ErrorOr<size_t> submit_bulk_transfer(Transfer& transfer) = 0;
+    virtual ErrorOr<void> submit_async_interrupt_transfer(NonnullLockRefPtr<Transfer> transfer, u16 ms_interval) = 0;
 
     u8 allocate_address();
 
diff --git a/Kernel/Bus/USB/USBPipe.cpp b/Kernel/Bus/USB/USBPipe.cpp
index ac4c79bc57..9a97b6e608 100644
--- a/Kernel/Bus/USB/USBPipe.cpp
+++ b/Kernel/Bus/USB/USBPipe.cpp
@@ -50,7 +50,7 @@ ErrorOr<size_t> ControlPipe::control_transfer(u8 request_type, u8 request, u16 v
     usb_request.index = index;
     usb_request.length = length;
 
-    auto transfer = TRY(Transfer::try_create(*this, length, *m_dma_buffer));
+    auto transfer = TRY(Transfer::create(*this, length, *m_dma_buffer));
     transfer->set_setup_packet(usb_request);
 
     dbgln_if(USB_DEBUG, "ControlPipe: Transfer allocated @ {}", transfer->buffer_physical());
@@ -84,7 +84,7 @@ ErrorOr<size_t> BulkInPipe::bulk_in_transfer(size_t length, void* data)
 
     size_t transfer_length = 0;
 
-    auto transfer = TRY(Transfer::try_create(*this, length, *m_dma_buffer));
+    auto transfer = TRY(Transfer::create(*this, length, *m_dma_buffer));
 
     dbgln_if(USB_DEBUG, "Pipe: Bulk in transfer allocated @ {}", transfer->buffer_physical());
     transfer_length = TRY(m_controller->submit_bulk_transfer(*transfer));
@@ -114,7 +114,7 @@ ErrorOr<size_t> BulkOutPipe::bulk_out_transfer(size_t length, void* data)
     MutexLocker lock(m_dma_buffer_lock);
 
     size_t transfer_length = 0;
-    auto transfer = TRY(Transfer::try_create(*this, length, *m_dma_buffer));
+    auto transfer = TRY(Transfer::create(*this, length, *m_dma_buffer));
 
     TRY(transfer->write_buffer(length, data));
     dbgln_if(USB_DEBUG, "Pipe: Bulk out transfer allocated @ {}", transfer->buffer_physical());
@@ -137,6 +137,16 @@ InterruptInPipe::InterruptInPipe(USBController const& controller, u8 endpoint_ad
 {
 }
 
+ErrorOr<NonnullLockRefPtr<Transfer>> InterruptInPipe::interrupt_in_transfer(size_t length, u16 ms_interval, USBAsyncCallback callback)
+{
+    VERIFY(length <= m_dma_buffer->size());
+
+    auto transfer = TRY(Transfer::create(*this, length, *m_dma_buffer, move(callback)));
+    dbgln_if(USB_DEBUG, "Pipe: Interrupt in transfer allocated @ {}", transfer->buffer_physical());
+    TRY(m_controller->submit_async_interrupt_transfer(transfer, ms_interval));
+    return transfer;
+}
+
 ErrorOr<NonnullOwnPtr<InterruptOutPipe>> InterruptOutPipe::create(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, u16 poll_interval, size_t buffer_size)
 {
     VERIFY(buffer_size >= max_packet_size);
diff --git a/Kernel/Bus/USB/USBPipe.h b/Kernel/Bus/USB/USBPipe.h
index 578852dc0f..6ccb6a205b 100644
--- a/Kernel/Bus/USB/USBPipe.h
+++ b/Kernel/Bus/USB/USBPipe.h
@@ -18,6 +18,8 @@ namespace Kernel::USB {
 class USBController;
 class Transfer;
 
+using USBAsyncCallback = Function<void(Transfer* transfer)>;
+
 //
 // A pipe is the logical connection between a memory buffer on the PC (host) and
 // an endpoint on the device. In this implementation, the data buffer the pipe connects
@@ -111,6 +113,8 @@ class InterruptInPipe : public Pipe {
 public:
     static ErrorOr<NonnullOwnPtr<InterruptInPipe>> create(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, u16 poll_interval, size_t buffer_size = PAGE_SIZE);
 
+    ErrorOr<NonnullLockRefPtr<Transfer>> interrupt_in_transfer(size_t length, u16 ms_interval, USBAsyncCallback callback);
+
     u16 poll_interval() const { return m_poll_interval; }
 
 private:
diff --git a/Kernel/Bus/USB/USBTransfer.cpp b/Kernel/Bus/USB/USBTransfer.cpp
index e3a0e75d3b..ada524d4f0 100644
--- a/Kernel/Bus/USB/USBTransfer.cpp
+++ b/Kernel/Bus/USB/USBTransfer.cpp
@@ -9,15 +9,16 @@
 
 namespace Kernel::USB {
 
-ErrorOr<NonnullLockRefPtr<Transfer>> Transfer::try_create(Pipe& pipe, u16 length, Memory::Region& dma_buffer)
+ErrorOr<NonnullLockRefPtr<Transfer>> Transfer::create(Pipe& pipe, u16 length, Memory::Region& dma_buffer, USBAsyncCallback callback)
 {
-    return adopt_nonnull_lock_ref_or_enomem(new (nothrow) Transfer(pipe, length, dma_buffer));
+    return adopt_nonnull_lock_ref_or_enomem(new (nothrow) Transfer(pipe, length, dma_buffer, move(callback)));
 }
 
-Transfer::Transfer(Pipe& pipe, u16 len, Memory::Region& dma_buffer)
+Transfer::Transfer(Pipe& pipe, u16 len, Memory::Region& dma_buffer, USBAsyncCallback callback)
     : m_pipe(pipe)
     , m_dma_buffer(dma_buffer)
     , m_transfer_data_size(len)
+    , m_callback(move(callback))
 {
 }
 
@@ -49,4 +50,10 @@ ErrorOr<void> Transfer::write_buffer(u16 len, void* data)
     return {};
 }
 
+void Transfer::invoke_async_callback()
+{
+    if (m_callback)
+        m_callback(this);
+}
+
 }
diff --git a/Kernel/Bus/USB/USBTransfer.h b/Kernel/Bus/USB/USBTransfer.h
index 5923542d6c..c506650d9e 100644
--- a/Kernel/Bus/USB/USBTransfer.h
+++ b/Kernel/Bus/USB/USBTransfer.h
@@ -20,7 +20,7 @@ namespace Kernel::USB {
 
 class Transfer final : public AtomicRefCounted<Transfer> {
 public:
-    static ErrorOr<NonnullLockRefPtr<Transfer>> try_create(Pipe&, u16 length, Memory::Region& dma_buffer);
+    static ErrorOr<NonnullLockRefPtr<Transfer>> create(Pipe&, u16 length, Memory::Region& dma_buffer, USBAsyncCallback callback = nullptr);
 
     Transfer() = delete;
     ~Transfer();
@@ -41,14 +41,17 @@ public:
     bool complete() const { return m_complete; }
     bool error_occurred() const { return m_error_occurred; }
 
+    void invoke_async_callback();
+
 private:
-    Transfer(Pipe& pipe, u16 len, Memory::Region& dma_buffer);
+    Transfer(Pipe& pipe, u16 len, Memory::Region& dma_buffer, USBAsyncCallback callback);
     Pipe& m_pipe;                    // Pipe that initiated this transfer
     Memory::Region& m_dma_buffer;    // DMA buffer
     USBRequestData m_request;        // USB request
     u16 m_transfer_data_size { 0 };  // Size of the transfer's data stage
     bool m_complete { false };       // Has this transfer been completed?
     bool m_error_occurred { false }; // Did an error occur during this transfer?
+    USBAsyncCallback m_callback { nullptr };
 };
 
 }