cpu. arch: add initiateMemRead() to ExecContext interface

For historical reasons, the ExecContext interface had a single
function, readMem(), that did two different things depending on
whether the ExecContext supported atomic memory mode (i.e.,
AtomicSimpleCPU) or timing memory mode (all the other models).
In the former case, it actually performed a memory read; in the
latter case, it merely initiated a read access, and the read
completion did not happen until later when a response packet
arrived from the memory system.

This led to some confusing things, including timing accesses
being required to provide a pointer for the return data even
though that pointer was only used in atomic mode.

This patch splits this interface, adding a new initiateMemRead()
function to the ExecContext interface to replace the timing-mode
use of readMem().

For consistency and clarity, the readMemTiming() helper function
in the ISA definitions is renamed to initiateMemRead() as well.
For x86, where the access size is passed in explicitly, we can
also get rid of the data parameter at this level.  For other ISAs,
where the access size is determined from the type of the data
parameter, we have to keep the parameter for that purpose.

6 files changed, 25 insertions, 0 deletions

diff --git a/src/cpu/simple/atomic.cc b/src/cpu/simple/atomic.cc
index 77706966b..4afd019d0 100644
--- a/src/cpu/simple/atomic.cc
+++ b/src/cpu/simple/atomic.cc
@@ -415,6 +415,12 @@ AtomicSimpleCPU::readMem(Addr addr, uint8_t * data,
     }
 }
 
+Fault
+AtomicSimpleCPU::initiateMemRead(Addr addr, unsigned size, unsigned flags)
+{
+    panic("initiateMemRead() is for timing accesses, and should "
+          "never be called on AtomicSimpleCPU.\n");
+}
 
 Fault
 AtomicSimpleCPU::writeMem(uint8_t *data, unsigned size,
diff --git a/src/cpu/simple/atomic.hh b/src/cpu/simple/atomic.hh
index 1a2f19949..c643bfe58 100644
--- a/src/cpu/simple/atomic.hh
+++ b/src/cpu/simple/atomic.hh
@@ -205,6 +205,8 @@ class AtomicSimpleCPU : public BaseSimpleCPU
     Fault readMem(Addr addr, uint8_t *data, unsigned size,
                   unsigned flags) override;
 
+    Fault initiateMemRead(Addr addr, unsigned size, unsigned flags) override;
+
     Fault writeMem(uint8_t *data, unsigned size,
                    Addr addr, unsigned flags, uint64_t *res) override;
 
diff --git a/src/cpu/simple/base.hh b/src/cpu/simple/base.hh
index 0ec9e502b..9164a2960 100644
--- a/src/cpu/simple/base.hh
+++ b/src/cpu/simple/base.hh
@@ -145,6 +145,8 @@ class BaseSimpleCPU : public BaseCPU
     virtual Fault readMem(Addr addr, uint8_t* data, unsigned size,
                           unsigned flags) = 0;
 
+    virtual Fault initiateMemRead(Addr addr, unsigned size, unsigned flags) = 0;
+
     virtual Fault writeMem(uint8_t* data, unsigned size, Addr addr,
                            unsigned flags, uint64_t* res) = 0;
 
diff --git a/src/cpu/simple/exec_context.hh b/src/cpu/simple/exec_context.hh
index 43a012404..f9d80d0d5 100644
--- a/src/cpu/simple/exec_context.hh
+++ b/src/cpu/simple/exec_context.hh
@@ -291,6 +291,12 @@ class SimpleExecContext : public ExecContext {
         return cpu->readMem(addr, data, size, flags);
     }
 
+    Fault initiateMemRead(Addr addr, unsigned int size,
+                          unsigned int flags) override
+    {
+        return cpu->initiateMemRead(addr, size, flags);
+    }
+
     Fault writeMem(uint8_t *data, unsigned int size, Addr addr,
                    unsigned int flags, uint64_t *res) override
     {
diff --git a/src/cpu/simple/timing.cc b/src/cpu/simple/timing.cc
index 6d67f610b..441d5f896 100644
--- a/src/cpu/simple/timing.cc
+++ b/src/cpu/simple/timing.cc
@@ -407,6 +407,13 @@ Fault
 TimingSimpleCPU::readMem(Addr addr, uint8_t *data,
                          unsigned size, unsigned flags)
 {
+    panic("readMem() is for atomic accesses, and should "
+          "never be called on TimingSimpleCPU.\n");
+}
+
+Fault
+TimingSimpleCPU::initiateMemRead(Addr addr, unsigned size, unsigned flags)
+{
     SimpleExecContext &t_info = *threadInfo[curThread];
     SimpleThread* thread = t_info.thread;
 
diff --git a/src/cpu/simple/timing.hh b/src/cpu/simple/timing.hh
index 36e01e9be..da8320793 100644
--- a/src/cpu/simple/timing.hh
+++ b/src/cpu/simple/timing.hh
@@ -286,6 +286,8 @@ class TimingSimpleCPU : public BaseSimpleCPU
     Fault readMem(Addr addr, uint8_t *data, unsigned size,
                   unsigned flags) override;
 
+    Fault initiateMemRead(Addr addr, unsigned size, unsigned flags) override;
+
     Fault writeMem(uint8_t *data, unsigned size,
                    Addr addr, unsigned flags, uint64_t *res) override;