Add HMER access syscalls (as fastpath).

Change-Id: Icc7494986d19950a18cc9ee53fd5125c86096a72
Reviewed-on: http://gfw160.austin.ibm.com:8080/gerrit/105
Tested-by: Jenkins Server
Reviewed-by: Douglas R. Gilbert <dgilbert@us.ibm.com>
Reviewed-by: Andrew J. Geissler <andrewg@us.ibm.com>

7 files changed, 115 insertions, 15 deletions

diff --git a/src/include/kernel/ppcconsts.S b/src/include/kernel/ppcconsts.S
index ae972f269..38fd5e6e5 100644
--- a/src/include/kernel/ppcconsts.S
+++ b/src/include/kernel/ppcconsts.S
@@ -102,6 +102,7 @@
                 .set HDEC,310
                 .set HSRR0,314
                 .set HSRR1,315
+                .set HMER,336
                 .set HID0,1008
                 .set PIR, 1023
 
diff --git a/src/include/kernel/syscalls.H b/src/include/kernel/syscalls.H
index 330db6922..1b87c5019 100644
--- a/src/include/kernel/syscalls.H
+++ b/src/include/kernel/syscalls.H
@@ -1,36 +1,81 @@
+/** @file syscalls.H
+ *  @brief Defines all the system call IDs to be shared between the kernel and
+ *         the system libc.
+ */
+
 #ifndef __KERNEL_SYSCALLS_H
 #define __KERNEL_SYSCALLS_H
 
 namespace Systemcalls
 {
+    /** @enum SysCalls
+     *  @brief List of normal system calls and their IDs.
+     *
+     *  These are passed by userspace code via r3 when the sc instruction is
+     *  executed.  The kernel performs a case statement to switch to the
+     *  appropriate system call handler.
+     */
     enum SysCalls
     {
+            /** task_yield() */
 	TASK_YIELD = 0,
+            /** task_create() */
 	TASK_START,
+            /** task_end() */
 	TASK_END,
-	TASK_GETTID,
-
+            
+            /** mutex_create() */
 	MUTEX_CREATE,
+            /** mutex_destroy() */
 	MUTEX_DESTROY,
+            /** mutex_lock() */
 	MUTEX_LOCK_CONTESTED,
+            /** mutex_unlock() */
 	MUTEX_UNLOCK_CONTESTED,
-
+            
+            /** msgq_create() */
 	MSGQ_CREATE,
+            /** msgq_destroy() */
 	MSGQ_DESTROY,
+            /** VFS internal */
 	MSGQ_REGISTER_ROOT,
+            /** VFS internal */
 	MSGQ_RESOLVE_ROOT,
-
+            
+            /** msg_send() */
 	MSG_SEND,
+            /** msg_sendrecv() */
 	MSG_SENDRECV,
+            /** msg_respond() */
 	MSG_RESPOND,
+            /** msg_wait() */
 	MSG_WAIT,
 
+            /** mmio_map() */
 	MMIO_MAP,
+            /** mmio_unmap() */
 	MMIO_UNMAP,
 
+            /** nanosleep() */
 	TIME_NANOSLEEP,
 
 	SYSCALL_MAX
     };
+
+    /** @enum SysCalls_FastPath
+     *  @brief List of fast-path system calls and their IDs.
+     *
+     *  @note If any of these change, their handling in start.S must also be
+     *        updated.  The ASM code relies on these values.
+     */
+    enum SysCalls_FastPath
+    {
+            /** mmio_hmer_read() */
+        MMIO_HMER_READ = 0x0800,
+            /** mmio_hmer_write() */
+        MMIO_HMER_WRITE = 0x0801,
+
+        SYSCALL_FASTPATH_MAX
+    };
 };
 #endif
diff --git a/src/include/sys/mmio.h b/src/include/sys/mmio.h
index 6a0e7a02b..eb146da72 100644
--- a/src/include/sys/mmio.h
+++ b/src/include/sys/mmio.h
@@ -11,6 +11,20 @@ extern "C"
 void* mmio_map(void* ra, size_t pages);
 int mmio_unmap(void* ea, size_t pages);
 
+/** @fn mmio_hmer_read()
+ *  @brief Reads the protected HMER register.
+ */
+uint64_t mmio_hmer_read();
+
+/** @fn mmio_hmer_write()
+ *  @brief Writes the protected HMER register.
+ *
+ *  @param[in] value - The value to write into the HMER.
+ *
+ *  @returns 0.
+ */
+int mmio_hmer_write(uint64_t value);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/kernel/start.S b/src/kernel/start.S
index 7eaf1fdf9..ac57926b4 100644
--- a/src/kernel/start.S
+++ b/src/kernel/start.S
@@ -126,7 +126,24 @@ STD_INTERRUPT(prog_ex, 0x700)
 UNIMPL_INTERRUPT(fp_unavail, 0x800)
 STD_INTERRUPT(decrementer, 0x900)
 UNIMPL_INTERRUPT(hype_decrementer, 0x980)
-STD_INTERRUPT(system_call, 0xC00)
+
+;// System Call Exception Vector
+;//
+;// This exception vector implements the save/restore for normal system calls
+;// that require C++ code for handling but also implements a fast-path for
+;// some simple calls, such as reading protected SPRs.
+;//
+;// Since this is called from userspace as a function call (see __syscall* 
+;// functions) we only need to honor the ELF ABI calling conventions.  That
+;// means some registers and condition fields can be considered volatile and
+;// modified prior to being saved.
+;//
+.org _start + 0xC00
+intvect_system_call_fast:
+    cmpi cr0, r3, 0x0800
+    bge  cr0, system_call_fast_path  
+STD_INTERRUPT(system_call, 0xC08)
+
 UNIMPL_INTERRUPT(trace, 0xD00)
 UNIMPL_INTERRUPT(hype_data_storage, 0xE00)
 UNIMPL_INTERRUPT(hype_inst_storage, 0xE20)
@@ -320,6 +337,29 @@ kernel_dispatch_task:
 			
     rfid			;// Execute task.
 
+    ;// @fn system_call_fast_path
+    ;// Handle fast path system calls.
+    ;//         0x800 = HMER read (HMER -> r3).
+    ;//         0x801 = HMER write (r4 -> HMER).
+system_call_fast_path:
+        ;// Check if this is HMER read (0x800).
+        ;// Compare was already done in system call path.
+    bne cr0, 2f
+    mfspr r3, HMER
+    b 1f                        ;// Jump to exit point.
+        ;// Check if this is HMER write (0x801).
+2:
+    cmpi cr0, r3, 0x801
+    bne cr0, 3f
+    mtspr HMER, r4
+    li r3, 0
+    b 1f                        ;// Jump to exit point.
+        ;// Invalid system call, loop for debug.
+3:
+    b 3b
+1:
+    rfid                        ;// Return from interrupt.
+
 .section .data
     .balign 1024
 kernel_stack:
diff --git a/src/kernel/syscall.C b/src/kernel/syscall.C
index 340250f50..837ed3d21 100644
--- a/src/kernel/syscall.C
+++ b/src/kernel/syscall.C
@@ -47,7 +47,6 @@ namespace Systemcalls
 	    &TaskYield,
 	    &TaskStart,
 	    &TaskEnd,
-	    &TaskGettid,
 
 	    &MutexCreate,
 	    &MutexDestroy,
@@ -134,11 +133,6 @@ namespace Systemcalls
 	delete t;
     }
 
-    void TaskGettid(task_t* t)
-    {
-	TASK_SETRTN(t, t->tid);
-    }
-
     void MutexCreate(task_t* t)
     {
 	UserMutex * m = new UserMutex();
diff --git a/src/lib/syscall_mmio.C b/src/lib/syscall_mmio.C
index f2dc8ccf8..30ec5bd37 100644
--- a/src/lib/syscall_mmio.C
+++ b/src/lib/syscall_mmio.C
@@ -12,3 +12,13 @@ int mmio_unmap(void* ea, size_t pages)
 {
     return (int64_t) _syscall2(MMIO_UNMAP, ea, (void*)pages);
 }
+
+uint64_t mmio_hmer_read()
+{
+    return (uint64_t) _syscall0(MMIO_HMER_READ);
+}
+
+int mmio_hmer_write(uint64_t value)
+{
+    return (int)(int64_t)_syscall1(MMIO_HMER_WRITE, (void*)value);
+}
diff --git a/src/lib/syscall_task.C b/src/lib/syscall_task.C
index fcedcb64b..b133ef2e4 100644
--- a/src/lib/syscall_task.C
+++ b/src/lib/syscall_task.C
@@ -32,13 +32,9 @@ void task_end()
 
 tid_t task_gettid()
 {
-    // Even though we have a syscall for GETTID, we also have the task in 
-    // GRP13.
-
     register task_t* task;
     asm volatile("mr %0, 13" : "=r"(task));
     return task->tid;
-    //return (tid_t)_syscall0(TASK_GETTID);
 }
 
 cpuid_t task_getcpuid()