/*
   * 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/irqflags.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

  	TRACE_IRQS_OFF

  	/* Function to be invoked passed stack pad slot 5 */
  	lw	t0,PT_PADSLOT5(sp)
  	/* Argument from sender passed in stack pad slot 4 */

  	lw	a0,PT_PADSLOT4(sp)

  	LONG_L	s0, TI_REGS($28)
  	LONG_S	sp, TI_REGS($28)
  	PTR_LA	ra, ret_from_irq

  	jr	t0

  
  /*
   * 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)