From 28baebae73c3ea8b75c7cae225a7db817ab825a9 Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 14 Feb 2006 13:53:20 -0800 Subject: [PATCH] FRV: Use virtual interrupt disablement Make the FRV arch use virtual interrupt disablement because accesses to the processor status register (PSR) are relatively slow and because we will soon have the need to deal with multiple interrupt controls at the same time (separate h/w and inter-core interrupts). The way this is done is to dedicate one of the four integer condition code registers (ICC2) to maintaining a virtual interrupt disablement state whilst inside the kernel. This uses the ICC2.Z flag (Zero) to indicate whether the interrupts are virtually disabled and the ICC2.C flag (Carry) to indicate whether the interrupts are physically disabled. ICC2.Z is set to indicate interrupts are virtually disabled. ICC2.C is set to indicate interrupts are physically enabled. Under normal running conditions Z==0 and C==1. Disabling interrupts with local_irq_disable() doesn't then actually physically disable interrupts - it merely sets ICC2.Z to 1. Should an interrupt then happen, the exception prologue will note ICC2.Z is set and branch out of line using one instruction (an unlikely BEQ). Here it will physically disable interrupts and clear ICC2.C. When it comes time to enable interrupts (local_irq_enable()), this simply clears the ICC2.Z flag and invokes a trap #2 if both Z and C flags are clear (the HI integer condition). This can be done with the TIHI conditional trap instruction. The trap then physically reenables interrupts and sets ICC2.C again. Upon returning the interrupt will be taken as interrupts will then be enabled. Note that whilst processing the trap, the whole exceptions system is disabled, and so an interrupt can't happen till it returns. If no pending interrupt had happened, ICC2.C would still be set, the HI condition would not be fulfilled, and no trap will happen. Saving interrupts (local_irq_save) is simply a matter of pulling the ICC2.Z flag out of the CCR register, shifting it down and masking it off. This gives a result of 0 if interrupts were enabled and 1 if they weren't. Restoring interrupts (local_irq_restore) is then a matter of taking the saved value mentioned previously and XOR'ing it against 1. If it was one, the result will be zero, and if it was zero the result will be non-zero. This result is then used to affect the ICC2.Z flag directly (it is a condition code flag after all). An XOR instruction does not affect the Carry flag, and so that bit of state is unchanged. The two flags can then be sampled to see if they're both zero using the trap (TIHI) as for the unconditional reenablement (local_irq_enable). This patch also: (1) Modifies the debugging stub (break.S) to handle single-stepping crossing into the trap #2 handler and into virtually disabled interrupts. (2) Removes superseded fixup pointers from the second instructions in the trap tables (there's no a separate fixup table for this). (3) Declares the trap #3 vector for use in .org directives in the trap table. (4) Moves irq_enter() and irq_exit() in do_IRQ() to avoid problems with virtual interrupt handling, and removes the duplicate code that has now been folded into irq_exit() (softirq and preemption handling). (5) Tells the compiler in the arch Makefile that ICC2 is now reserved. (6) Documents the in-kernel ABI, including the virtual interrupts. (7) Renames the old irq management functions to different names. Signed-off-by: David Howells Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/frv/kernel/entry-table.S | 39 ++++++++++++++++++++++++++++++++++----- 1 file changed, 34 insertions(+), 5 deletions(-) (limited to 'arch/frv/kernel/entry-table.S') diff --git a/arch/frv/kernel/entry-table.S b/arch/frv/kernel/entry-table.S index 9b9243e2103c..81568acea9cd 100644 --- a/arch/frv/kernel/entry-table.S +++ b/arch/frv/kernel/entry-table.S @@ -116,6 +116,8 @@ __break_kerneltrap_fixup_table: .long __break_step_uspace_external_interrupt .section .trap.kernel .org \tbr_tt + # deal with virtual interrupt disablement + beq icc2,#0,__entry_kernel_external_interrupt_virtually_disabled bra __entry_kernel_external_interrupt .section .trap.fixup.kernel .org \tbr_tt >> 2 @@ -259,25 +261,52 @@ __trap_fixup_kernel_data_tlb_miss: .org TBR_TT_TRAP0 .rept 127 bra __entry_uspace_softprog_interrupt - bra __break_step_uspace_softprog_interrupt - .long 0,0 + .long 0,0,0 .endr .org TBR_TT_BREAK bra __entry_break .long 0,0,0 + .section .trap.fixup.user + .org TBR_TT_TRAP0 >> 2 + .rept 127 + .long __break_step_uspace_softprog_interrupt + .endr + .org TBR_TT_BREAK >> 2 + .long 0 + # miscellaneous kernel mode entry points .section .trap.kernel .org TBR_TT_TRAP0 - .rept 127 bra __entry_kernel_softprog_interrupt - bra __break_step_kernel_softprog_interrupt - .long 0,0 + .org TBR_TT_TRAP1 + bra __entry_kernel_softprog_interrupt + + # trap #2 in kernel - reenable interrupts + .org TBR_TT_TRAP2 + bra __entry_kernel_external_interrupt_virtual_reenable + + # miscellaneous kernel traps + .org TBR_TT_TRAP3 + .rept 124 + bra __entry_kernel_softprog_interrupt + .long 0,0,0 .endr .org TBR_TT_BREAK bra __entry_break .long 0,0,0 + .section .trap.fixup.kernel + .org TBR_TT_TRAP0 >> 2 + .long __break_step_kernel_softprog_interrupt + .long __break_step_kernel_softprog_interrupt + .long __break_step_kernel_external_interrupt_virtual_reenable + .rept 124 + .long __break_step_kernel_softprog_interrupt + .endr + .org TBR_TT_BREAK >> 2 + .long 0 + # miscellaneous debug mode entry points .section .trap.break .org TBR_TT_BREAK -- cgit v1.2.3