[Qemu-devel] [PATCH 4/9] hw/mips: implement ITC Storage - Empty/Full Sync and Try Views

[Leon Alrae <leon.alrae@imgtec.com>]

Empty/Full Synchronized and Try views can be used to access FIFO cells.
Store to the FIFO cell pushes the value into the queue, load pops the oldest
element from the queue. Cell's Full and Empty bits are automatically updated
to reflect new state of the cell.

Empty/Full Synchronized View causes the issuing thread to block when FIFO is
empty while thread is performing a read, or FIFO is full while thread is
performing a write.

Empty/Full Try View never blocks the thread. If cell is full then write is
ignored, if cell is empty then load returns 0.

Trap bit (i.e. Gating Storage exceptions) not implemented.
Store Conditional support for E/F Try View (i.e. indicate failure if FIFO
is full) not implemented.

Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
---
 hw/misc/mips_itu.c | 113 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 113 insertions(+)

diff --git a/hw/misc/mips_itu.c b/hw/misc/mips_itu.c
index 0864957..9ef5619 100644
--- a/hw/misc/mips_itu.c
+++ b/hw/misc/mips_itu.c
@@ -152,6 +152,26 @@ static inline ITCStorageCell *get_cell(MIPSITUState *s,
     return &s->cell[cell_idx];
 }
 
+static void wake_blocked_threads(ITCStorageCell *c)
+{
+    CPUState *cs;
+    CPU_FOREACH(cs) {
+        if (cs->halted && (c->blocked_threads & (1ULL << cs->cpu_index))) {
+            cpu_interrupt(cs, CPU_INTERRUPT_WAKE);
+        }
+    }
+    c->blocked_threads = 0;
+}
+
+static void QEMU_NORETURN block_thread_and_exit(ITCStorageCell *c)
+{
+    c->blocked_threads |= 1ULL << current_cpu->cpu_index;
+    cpu_restore_state(current_cpu, current_cpu->mem_io_pc);
+    current_cpu->halted = 1;
+    current_cpu->exception_index = EXCP_HLT;
+    cpu_loop_exit(current_cpu);
+}
+
 /* ITC Control View */
 
 static inline uint64_t view_control_read(ITCStorageCell *c)
@@ -175,6 +195,87 @@ static inline void view_control_write(ITCStorageCell *c, uint64_t val)
     }
 }
 
+/* ITC Empty/Full View */
+
+static uint64_t view_ef_common_read(ITCStorageCell *c, bool blocking)
+{
+    uint64_t ret = 0;
+
+    if (!c->tag.FIFO) {
+        return 0;
+    }
+
+    c->tag.F = 0;
+
+    if (blocking && c->tag.E) {
+        block_thread_and_exit(c);
+    }
+
+    if (c->blocked_threads) {
+        wake_blocked_threads(c);
+    }
+
+    if (c->tag.FIFOPtr > 0) {
+        ret = c->data[c->fifo_out];
+        c->fifo_out = (c->fifo_out + 1) % ITC_CELL_DEPTH;
+        c->tag.FIFOPtr--;
+    }
+
+    if (c->tag.FIFOPtr == 0) {
+        c->tag.E = 1;
+    }
+
+    return ret;
+}
+
+static uint64_t view_ef_sync_read(ITCStorageCell *c)
+{
+    return view_ef_common_read(c, true);
+}
+
+static uint64_t view_ef_try_read(ITCStorageCell *c)
+{
+    return view_ef_common_read(c, false);
+}
+
+static inline void view_ef_common_write(ITCStorageCell *c, uint64_t val,
+                                        bool blocking)
+{
+    if (!c->tag.FIFO) {
+        return;
+    }
+
+    c->tag.E = 0;
+
+    if (blocking && c->tag.F) {
+        block_thread_and_exit(c);
+    }
+
+    if (c->blocked_threads) {
+        wake_blocked_threads(c);
+    }
+
+    if (c->tag.FIFOPtr < ITC_CELL_DEPTH) {
+        int idx = (c->fifo_out + c->tag.FIFOPtr) % ITC_CELL_DEPTH;
+        c->data[idx] = val;
+        c->tag.FIFOPtr++;
+    }
+
+    if (c->tag.FIFOPtr == ITC_CELL_DEPTH) {
+        c->tag.F = 1;
+    }
+}
+
+static void view_ef_sync_write(ITCStorageCell *c, uint64_t val)
+{
+    view_ef_common_write(c, val, true);
+}
+
+static void view_ef_try_write(ITCStorageCell *c, uint64_t val)
+{
+    view_ef_common_write(c, val, false);
+}
+
 static uint64_t itc_storage_read(void *opaque, hwaddr addr, unsigned size)
 {
     MIPSITUState *s = (MIPSITUState *)opaque;
@@ -186,6 +287,12 @@ static uint64_t itc_storage_read(void *opaque, hwaddr addr, unsigned size)
     case ITCVIEW_CONTROL:
         ret = view_control_read(cell);
         break;
+    case ITCVIEW_EF_SYNC:
+        ret = view_ef_sync_read(cell);
+        break;
+    case ITCVIEW_EF_TRY:
+        ret = view_ef_try_read(cell);
+        break;
     default:
         qemu_log_mask(LOG_GUEST_ERROR,
                       "itc_storage_read: Bad ITC View %d\n", (int)view);
@@ -206,6 +313,12 @@ static void itc_storage_write(void *opaque, hwaddr addr, uint64_t data,
     case ITCVIEW_CONTROL:
         view_control_write(cell, data);
         break;
+    case ITCVIEW_EF_SYNC:
+        view_ef_sync_write(cell, data);
+        break;
+    case ITCVIEW_EF_TRY:
+        view_ef_try_write(cell, data);
+        break;
     default:
         qemu_log_mask(LOG_GUEST_ERROR,
                       "itc_storage_write: Bad ITC View %d\n", (int)view);
-- 
2.1.0