Kernel: Split I2C functionality from IntelNativeDisplayConnector code

Splitting the I2C-related code lets the DisplayConnector code to utilize
I2C operations without caring about the specific details of the hardware
and allow future expansion of the driver to other newer generations
sharing the same GMBus code.

We should require a timeout for GMBus operations always, because faulty
hardware could let us just spin forever. Also, if nothing is listening
to the bus (which should result in a NAK), we could also spin forever.

1 files changed, 123 insertions, 0 deletions

diff --git a/Kernel/Graphics/Intel/Auxiliary/GMBusConnector.cpp b/Kernel/Graphics/Intel/Auxiliary/GMBusConnector.cpp
new file mode 100644
index 0000000000..3b599d562d
--- /dev/null
+++ b/Kernel/Graphics/Intel/Auxiliary/GMBusConnector.cpp
@@ -0,0 +1,123 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Arch/Delay.h>
+#include <Kernel/Graphics/Intel/Auxiliary/GMBusConnector.h>
+#include <Kernel/PhysicalAddress.h>
+
+namespace Kernel {
+
+enum class GMBusStatus {
+    TransactionCompletion,
+    HardwareReady
+};
+
+enum GMBusCycle {
+    Wait = 1,
+    Stop = 4,
+};
+
+ErrorOr<NonnullOwnPtr<GMBusConnector>> GMBusConnector::create_with_physical_address(PhysicalAddress gmbus_start_address)
+{
+    auto registers_mapping = TRY(map_typed<GMBusRegisters volatile>(gmbus_start_address, sizeof(GMBusRegisters), Memory::Region::Access::ReadWrite));
+    return adopt_nonnull_own_or_enomem(new (nothrow) GMBusConnector(move(registers_mapping)));
+}
+
+GMBusConnector::GMBusConnector(Memory::TypedMapping<GMBusRegisters volatile> registers_mapping)
+    : m_gmbus_registers(move(registers_mapping))
+{
+    set_default_rate();
+    set_pin_pair(PinPair::DedicatedAnalog);
+}
+
+bool GMBusConnector::wait_for(GMBusStatus desired_status, size_t milliseconds_timeout)
+{
+    VERIFY(m_access_lock.is_locked());
+    size_t milliseconds_passed = 0;
+    while (1) {
+        if (milliseconds_timeout < milliseconds_passed)
+            return false;
+        full_memory_barrier();
+        u32 status = m_gmbus_registers->status;
+        full_memory_barrier();
+        VERIFY(!(status & (1 << 10))); // error happened
+        switch (desired_status) {
+        case GMBusStatus::HardwareReady:
+            if (status & (1 << 11))
+                return true;
+            break;
+        case GMBusStatus::TransactionCompletion:
+            if (status & (1 << 14))
+                return true;
+            break;
+        default:
+            VERIFY_NOT_REACHED();
+        }
+        microseconds_delay(1000);
+        milliseconds_passed++;
+    }
+}
+
+ErrorOr<void> GMBusConnector::write(unsigned address, u32 data)
+{
+    VERIFY(address < 256);
+    SpinlockLocker locker(m_access_lock);
+    full_memory_barrier();
+    m_gmbus_registers->data = data;
+    full_memory_barrier();
+    m_gmbus_registers->command = ((address << 1) | (1 << 16) | (GMBusCycle::Wait << 25) | (1 << 30));
+    full_memory_barrier();
+    if (!wait_for(GMBusStatus::TransactionCompletion, 250))
+        return Error::from_errno(EBUSY);
+    return {};
+}
+
+void GMBusConnector::set_default_rate()
+{
+    // FIXME: Verify GMBUS Rate Select is set only when GMBUS is idle
+    SpinlockLocker locker(m_access_lock);
+    // Set the rate to 100KHz
+    m_gmbus_registers->clock = m_gmbus_registers->clock & ~(0b111 << 8);
+}
+
+void GMBusConnector::set_pin_pair(PinPair pin_pair)
+{
+    // FIXME: Verify GMBUS is idle
+    SpinlockLocker locker(m_access_lock);
+    m_gmbus_registers->clock = (m_gmbus_registers->clock & (~0b111)) | (pin_pair & 0b111);
+}
+
+ErrorOr<void> GMBusConnector::read(unsigned address, u8* buf, size_t length)
+{
+    VERIFY(address < 256);
+    SpinlockLocker locker(m_access_lock);
+    size_t nread = 0;
+    auto read_set = [&] {
+        full_memory_barrier();
+        u32 data = m_gmbus_registers->data;
+        full_memory_barrier();
+        for (size_t index = 0; index < 4; index++) {
+            if (nread == length)
+                break;
+            buf[nread] = (data >> (8 * index)) & 0xFF;
+            nread++;
+        }
+    };
+
+    full_memory_barrier();
+    m_gmbus_registers->command = (1 | (address << 1) | (length << 16) | (GMBusCycle::Wait << 25) | (1 << 30));
+    full_memory_barrier();
+    while (nread < length) {
+        if (!wait_for(GMBusStatus::HardwareReady, 250))
+            return Error::from_errno(EBUSY);
+        read_set();
+    }
+    if (!wait_for(GMBusStatus::TransactionCompletion, 250))
+        return Error::from_errno(EBUSY);
+    return {};
+}
+
+}