metag: handle low level kicks directly

Kick interrupts trigger the LWK (low level kick) signal, usually handled
by the __TBIDoStdLWK() function which is the only handler inherited from
the bootloader. The LWK signal is converted either to a SWK (plain
software kick) or a SWS (software kick with an attached message).

Linux has kick_handler() to handle SWK and call registered kick handlers
(IPIs and inter-thread comms), but SWS is as far as I'm aware unused
with Linux.

Therefore remove that abstraction and have Linux handle LWK directly.
This will reduce kick latency slightly, and reduce our dependence on the
bootloader, which makes it easier to directly boot a kernel in QEMU
(particularly for SMP).
Signed-off-by: James Hogan <james.hogan@imgtec.com>

arch/metag/include/asm/tbx.h

@@ -150,11 +150,9 @@
 #else
 /* Reserved 0x04-0x09 */
 #endif
-#define TBID_SIGNUM_SWS     0x0A /* KICK received with SigMask != 0 */
-#define TBID_SIGNUM_SWK     0x0B /* KICK received with SigMask == 0 */
-/* Reserved 0x0C-0x0F */
+/* Reserved 0x0A-0x0F */
 #define TBID_SIGNUM_TRT     0x10 /* Timer trigger */
-#define TBID_SIGNUM_LWK     0x11 /* Low level kick (handler provided by TBI) */
+#define TBID_SIGNUM_LWK     0x11 /* Low level kick */
 #define TBID_SIGNUM_XXF     0x12 /* Fault handler - receives ALL _xxF sigs */
 #ifdef TBI_1_4
 #define TBID_SIGNUM_DFR     0x13 /* Deferred Exception handler */
@@ -183,8 +181,7 @@
    each hardware signal, sometimes this is a many-to-one relationship. */
 #define TBI_TRIG_BIT(SigNum)                                      (\
     ((SigNum) >= TBID_SIGNUM_TRT) ? 1<<((SigNum)-TBID_SIGNUM_TRT) :\
-    ( ((SigNum) == TBID_SIGNUM_SWS) ||                             \
-      ((SigNum) == TBID_SIGNUM_SWK)    ) ?                         \
+    ((SigNum) == TBID_SIGNUM_LWK) ?                                \
                          TXSTAT_KICK_BIT : TXSTATI_BGNDHALT_BIT    )
 
 /* Return the hardware trigger vector number for entries in the
@@ -687,10 +684,8 @@ typedef union _tbires_tag_ {
    Triggers will indicate the status of TXSTAT or TXSTATI sampled by the
           code that called the handler.
           
-   InstOrSWSId is defined firstly as 'Inst' if the SigNum is TBID_SIGNUM_SWx
-          and hold the actual SWITCH instruction detected, secondly if SigNum
-          is TBID_SIGNUM_SWS the 'SWSId' is defined to hold the Id of the
-          software signal detected, in other cases the value of this
+   Inst is defined as 'Inst' if the SigNum is TBID_SIGNUM_SWx and holds the
+          actual SWITCH instruction detected, in other cases the value of this
           parameter is undefined.
    
    pTBI   points at the PTBI structure related to the thread and processing
@@ -709,7 +704,7 @@ typedef union _tbires_tag_ {
 
  */
 typedef TBIRES (*PTBIAPIFN)( TBIRES State, int SigNum,
-                             int Triggers, int InstOrSWSId,
+                             int Triggers, int Inst,
                              volatile struct _tbi_tag_ *pTBI );
 #endif /* ifndef __ASSEMBLY__ */
 
@@ -757,7 +752,7 @@ typedef volatile struct _tbi_tag_ {
 #ifndef __ASSEMBLY__
 /* This handler should be used for TBID_SIGNUM_DFR */
 extern TBIRES __TBIHandleDFR ( TBIRES State, int SigNum,
-                               int Triggers, int InstOrSWSId,
+                               int Triggers, int Inst,
                                volatile struct _tbi_tag_ *pTBI );
 #endif
 #endif

arch/metag/kernel/setup.c

@@ -302,13 +302,9 @@ void __init setup_arch(char **cmdline_p)
 	 * rather than the version from the bootloader. This makes call
 	 * stacks easier to understand and may allow us to unmap the
 	 * bootloader at some point.
-	 *
-	 * We need to keep the LWK handler that TBI installed in order to
-	 * be able to do inter-thread comms.
 	 */
 	for (i = 0; i <= TBID_SIGNUM_MAX; i++)
-		if (i != TBID_SIGNUM_LWK)
-			_pTBI->fnSigs[i] = __TBIUnExpXXX;
+		_pTBI->fnSigs[i] = __TBIUnExpXXX;
 
 	/* A Meta requirement is that the kernel is loaded (virtually)
 	 * at the PAGE_OFFSET.

arch/metag/kernel/traps.c

@@ -819,8 +819,7 @@ void per_cpu_trap_init(unsigned long cpu)
 
 	set_trigger_mask(TBI_INTS_INIT(thread) | /* interrupts */
 			 TBI_TRIG_BIT(TBID_SIGNUM_LWK) | /* low level kick */
-			 TBI_TRIG_BIT(TBID_SIGNUM_SW1) |
-			 TBI_TRIG_BIT(TBID_SIGNUM_SWS));
+			 TBI_TRIG_BIT(TBID_SIGNUM_SW1));
 
 	/* non-priv - use current stack */
 	int_context.Sig.pCtx = NULL;
@@ -842,7 +841,7 @@ void __init trap_init(void)
 	_pTBI->fnSigs[TBID_SIGNUM_SW1] = switch1_handler;
 	_pTBI->fnSigs[TBID_SIGNUM_SW2] = switchx_handler;
 	_pTBI->fnSigs[TBID_SIGNUM_SW3] = switchx_handler;
-	_pTBI->fnSigs[TBID_SIGNUM_SWK] = kick_handler;
+	_pTBI->fnSigs[TBID_SIGNUM_LWK] = kick_handler;
 
 #ifdef CONFIG_METAG_META21
 	_pTBI->fnSigs[TBID_SIGNUM_DFR] = __TBIHandleDFR;

arch/metag/tbx/tbidefr.S

@@ -20,7 +20,7 @@
 /* D1Ar1:D0Ar2 -- State
  * D0Ar3       -- SigNum
  * D0Ar4       -- Triggers
- * D1Ar5       -- InstOrSWSId
+ * D1Ar5       -- Inst
  * D0Ar6       -- pTBI (volatile)
  */
 ___TBIHandleDFR: