From 291364e1b408d29236034854b7ed30f080e5b6c9 Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Wed, 1 Nov 2023 18:41:44 +0100
Subject: lt_bus: add initial support for global bus locking

---
 src/models/lt_bus.h | 101 ++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 95 insertions(+), 6 deletions(-)

(limited to 'src/models/lt_bus.h')

diff --git a/src/models/lt_bus.h b/src/models/lt_bus.h
index cf09d99..86b181e 100644
--- a/src/models/lt_bus.h
+++ b/src/models/lt_bus.h
@@ -7,10 +7,42 @@
 #include "utils/tlm_target_socket_tagged.h"
 #include "utils/types.h"
 
+#include <sysc/kernel/sc_event.h>
+
 #include <algorithm>
 #include <memory>
 #include <vector>
 
+// TLM bus lock extension.
+//
+// This extension is used to implemented the bus locking scheme.
+// The protocol is as follows. Once an initiator sends a locked transaction,
+// the bus will be locked by that initiator after all currently pending
+// transactions are finished. The bus is locked until the locking initiator
+// sends an unlocked transaction.
+struct [[nodiscard]] bus_lock : tlm::tlm_extension<bus_lock> {
+  bool is_lock{false};
+
+  constexpr explicit bus_lock() = default;
+  constexpr explicit bus_lock(const bus_lock&) = default;
+
+  virtual tlm_extension_base* clone() const override {
+    return new bus_lock(*this);
+  }
+
+  virtual void copy_from(const tlm_extension_base& ext) override {
+    if (&ext == this) {
+      // Copy from self, nop.
+      return;
+    }
+
+    assert(typeid(this) == typeid(ext));
+    const bus_lock& other = static_cast<const bus_lock&>(ext);
+
+    is_lock = other.is_lock;
+  }
+};
+
 class lt_bus : public sc_core::sc_module {
   using target_socket = tlm_target_socket_tagged<lt_bus>;
   using target_socket_ptr = std::unique_ptr<target_socket>;
@@ -116,14 +148,60 @@ class lt_bus : public sc_core::sc_module {
 
   // -- TLM_FW_TRANSPORT_IF ----------------------------------------------------
 
-  void b_transport(usize, tlm::tlm_generic_payload& tx, sc_core::sc_time& t) {
+  void b_transport(usize idx,
+                   tlm::tlm_generic_payload& tx,
+                   sc_core::sc_time& t) {
     if (const auto r = decode(tx)) {
-      const auto tx_start = tx.get_address();
-      assert(r.start <= tx_start);
+      const auto do_tx = [&]() {
+        const auto tx_start = tx.get_address();
+        assert(r.start <= tx_start);
 
-      tx.set_address(tx_start - r.start);
-      (*r.sock)->b_transport(tx, t);
-      tx.set_address(tx_start);
+        tx.set_address(tx_start - r.start);
+        (*r.sock)->b_transport(tx, t);
+        tx.set_address(tx_start);
+      };
+
+      while (m_bl.is_locked && (m_bl.idx != idx)) {
+        wait(m_bl.ev_no_pending_tx);
+      }
+
+      const auto* ext = tx.get_extension<bus_lock>();
+      if (ext && ext->is_lock) {
+        assert(!m_bl.is_locked);
+
+        m_bl.is_locked = true;
+        m_bl.idx = idx;
+
+        if (m_bl.pending_tx) {
+          wait(m_bl.ev_no_pending_tx);
+        }
+        assert(m_bl.pending_tx == 0);
+
+        // Invalidate DMI pointers for the whole address space. This forces all
+        // initiators on the slow path and through the bus, which can than
+        // enforce the exclusive access.
+        for (auto& sock : m_initiators) {
+          (*sock)->invalidate_direct_mem_ptr(0, -1ull);
+        }
+
+        do_tx();
+        assert(m_bl.pending_tx == 0);
+      } else {
+        assert(!m_bl.is_locked || (m_bl.is_locked && m_bl.idx == idx));
+
+        m_bl.pending_tx++;
+        do_tx();
+        m_bl.pending_tx--;
+
+        if (m_bl.is_locked && m_bl.idx == idx) {
+          assert(m_bl.pending_tx == 0);
+          m_bl.is_locked = false;
+        }
+
+        if (m_bl.pending_tx == 0) {
+          m_bl.ev_no_pending_tx.notify(sc_core::SC_ZERO_TIME);
+        }
+      }
     } else {
       tx.set_response_status(tlm::TLM_ADDRESS_ERROR_RESPONSE);
     }
@@ -132,6 +210,10 @@ class lt_bus : public sc_core::sc_module {
   bool get_direct_mem_ptr(usize,
                           tlm::tlm_generic_payload& tx,
                           tlm::tlm_dmi& dmi) {
+    if (m_bl.is_locked) {
+      return false;
+    }
+
     if (const auto r = decode(tx)) {
       const auto tx_start = tx.get_address();
       assert(r.start <= tx_start);
@@ -245,6 +327,13 @@ class lt_bus : public sc_core::sc_module {
   std::vector<initiator_socket_ptr> m_targets;
   // Address range mappings to BUS TARGETs (m_tragets).
   std::vector<mapping> m_mappings;
+
+  struct bus_lock_state {
+    bool is_locked{false};
+    usize idx{0};
+    usize pending_tx{0};
+    sc_core::sc_event ev_no_pending_tx;
+  } m_bl;
 };
 
 #endif
-- 
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