[MIPS] MT: Improved multithreading support.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/kernel/smtc-asm.S b/arch/mips/kernel/smtc-asm.S
new file mode 100644
index 0000000..c9d6519
--- /dev/null
+++ b/arch/mips/kernel/smtc-asm.S
@@ -0,0 +1,130 @@
+/*
+ * Assembly Language Functions for MIPS MT SMTC support
+ */
+
+/*
+ * This file should be built into the kernel only if CONFIG_MIPS_MT_SMTC is set. */
+
+#include <asm/regdef.h>
+#include <asm/asmmacro.h>
+#include <asm/stackframe.h>
+#include <asm/stackframe.h>
+
+/*
+ * "Software Interrupt" linkage.
+ *
+ * This is invoked when an "Interrupt" is sent from one TC to another,
+ * where the TC to be interrupted is halted, has it's Restart address
+ * and Status values saved by the "remote control" thread, then modified
+ * to cause execution to begin here, in kenel mode. This code then
+ * disguises the TC state as that of an exception and transfers
+ * control to the general exception or vectored interrupt handler.
+ */
+ .set noreorder
+
+/*
+The __smtc_ipi_vector would use k0 and k1 as temporaries and
+1) Set EXL (this is per-VPE, so this can't be done by proxy!)
+2) Restore the K/CU and IXMT bits to the pre "exception" state
+ (EXL means no interrupts and access to the kernel map).
+3) Set EPC to be the saved value of TCRestart.
+4) Jump to the exception handler entry point passed by the sender.
+
+CAN WE PROVE THAT WE WON'T DO THIS IF INTS DISABLED??
+*/
+
+/*
+ * Reviled and slandered vision: Set EXL and restore K/CU/IXMT
+ * state of pre-halt thread, then save everything and call
+ * thought some function pointer to imaginary_exception, which
+ * will parse a register value or memory message queue to
+ * deliver things like interprocessor interrupts. On return
+ * from that function, jump to the global ret_from_irq code
+ * to invoke the scheduler and return as appropriate.
+ */
+
+#define PT_PADSLOT4 (PT_R0-8)
+#define PT_PADSLOT5 (PT_R0-4)
+
+ .text
+ .align 5
+FEXPORT(__smtc_ipi_vector)
+ .set noat
+ /* Disable thread scheduling to make Status update atomic */
+ DMT 27 # dmt k1
+ ehb
+ /* Set EXL */
+ mfc0 k0,CP0_STATUS
+ ori k0,k0,ST0_EXL
+ mtc0 k0,CP0_STATUS
+ ehb
+ /* Thread scheduling now inhibited by EXL. Restore TE state. */
+ andi k1,k1,VPECONTROL_TE
+ beqz k1,1f
+ emt
+1:
+ /*
+ * The IPI sender has put some information on the anticipated
+ * kernel stack frame. If we were in user mode, this will be
+ * built above the saved kernel SP. If we were already in the
+ * kernel, it will be built above the current CPU SP.
+ *
+ * Were we in kernel mode, as indicated by CU0?
+ */
+ sll k1,k0,3
+ .set noreorder
+ bltz k1,2f
+ move k1,sp
+ .set reorder
+ /*
+ * If previously in user mode, set CU0 and use kernel stack.
+ */
+ li k1,ST0_CU0
+ or k1,k1,k0
+ mtc0 k1,CP0_STATUS
+ ehb
+ get_saved_sp
+ /* Interrupting TC will have pre-set values in slots in the new frame */
+2: subu k1,k1,PT_SIZE
+ /* Load TCStatus Value */
+ lw k0,PT_TCSTATUS(k1)
+ /* Write it to TCStatus to restore CU/KSU/IXMT state */
+ mtc0 k0,$2,1
+ ehb
+ lw k0,PT_EPC(k1)
+ mtc0 k0,CP0_EPC
+ /* Save all will redundantly recompute the SP, but use it for now */
+ SAVE_ALL
+ CLI
+ move a0,sp
+ /* Function to be invoked passed stack pad slot 5 */
+ lw t0,PT_PADSLOT5(sp)
+ /* Argument from sender passed in stack pad slot 4 */
+ lw a1,PT_PADSLOT4(sp)
+ jalr t0
+ nop
+ j ret_from_irq
+ nop
+
+/*
+ * Called from idle loop to provoke processing of queued IPIs
+ * First IPI message in queue passed as argument.
+ */
+
+LEAF(self_ipi)
+ /* Before anything else, block interrupts */
+ mfc0 t0,CP0_TCSTATUS
+ ori t1,t0,TCSTATUS_IXMT
+ mtc0 t1,CP0_TCSTATUS
+ ehb
+ /* We know we're in kernel mode, so prepare stack frame */
+ subu t1,sp,PT_SIZE
+ sw ra,PT_EPC(t1)
+ sw a0,PT_PADSLOT4(t1)
+ la t2,ipi_decode
+ sw t2,PT_PADSLOT5(t1)
+ /* Save pre-disable value of TCStatus */
+ sw t0,PT_TCSTATUS(t1)
+ j __smtc_ipi_vector
+ nop
+END(self_ipi)