ARM: 8150/3: fiq: Replace default FIQ handler

This patch introduces a new default FIQ handler that is structured in a
similar way to the existing ARM exception handler and result in the FIQ
being handled by C code running on the SVC stack (despite this code run
in the FIQ handler is subject to severe limitations with respect to
locking making normal interaction with the kernel impossible).

This default handler allows concepts that on x86 would be handled using
NMIs to be realized on ARM.

Credit:

    This patch is a near complete re-write of a patch originally
    provided by Anton Vorontsov. Today only a couple of small fragments
    survive, however without Anton's work to build from this patch would
    not exist. Thanks also to Russell King for spoonfeeding me a variety
    of fixes during the review cycle.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 47 insertions, 0 deletions

diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S
index 2fdf8679b46e..0d91ca05d55b 100644
--- a/arch/arm/kernel/entry-header.S
+++ b/arch/arm/kernel/entry-header.S
@@ -216,6 +216,34 @@
 	ldmia	sp, {r0 - pc}^			@ load r0 - pc, cpsr
 	.endm
 
+	@
+	@ svc_exit_via_fiq - like svc_exit but switches to FIQ mode before exit
+	@
+	@ This macro acts in a similar manner to svc_exit but switches to FIQ
+	@ mode to restore the final part of the register state.
+	@
+	@ We cannot use the normal svc_exit procedure because that would
+	@ clobber spsr_svc (FIQ could be delivered during the first few
+	@ instructions of vector_swi meaning its contents have not been
+	@ saved anywhere).
+	@
+	@ Note that, unlike svc_exit, this macro also does not allow a caller
+	@ supplied rpsr. This is because the FIQ exceptions are not re-entrant
+	@ and the handlers cannot call into the scheduler (meaning the value
+	@ on the stack remains correct).
+	@
+	.macro  svc_exit_via_fiq
+	mov	r0, sp
+	ldmib	r0, {r1 - r14}	@ abort is deadly from here onward (it will
+				@ clobber state restored below)
+	msr	cpsr_c, #FIQ_MODE | PSR_I_BIT | PSR_F_BIT
+	add	r8, r0, #S_PC
+	ldr	r9, [r0, #S_PSR]
+	msr	spsr_cxsf, r9
+	ldr	r0, [r0, #S_R0]
+	ldmia	r8, {pc}^
+	.endm
+
 	.macro	restore_user_regs, fast = 0, offset = 0
 	ldr	r1, [sp, #\offset + S_PSR]	@ get calling cpsr
 	ldr	lr, [sp, #\offset + S_PC]!	@ get pc
@@ -267,6 +295,25 @@
 	rfeia	sp!
 	.endm
 
+	@
+	@ svc_exit_via_fiq - like svc_exit but switches to FIQ mode before exit
+	@
+	@ For full details see non-Thumb implementation above.
+	@
+	.macro  svc_exit_via_fiq
+	add	r0, sp, #S_R2
+	ldr	lr, [sp, #S_LR]
+	ldr	sp, [sp, #S_SP] @ abort is deadly from here onward (it will
+			        @ clobber state restored below)
+	ldmia	r0, {r2 - r12}
+	mov	r1, #FIQ_MODE | PSR_I_BIT | PSR_F_BIT
+	msr	cpsr_c, r1
+	sub	r0, #S_R2
+	add	r8, r0, #S_PC
+	ldmia	r0, {r0 - r1}
+	rfeia	r8
+	.endm
+
 #ifdef CONFIG_CPU_V7M
 	/*
 	 * Note we don't need to do clrex here as clearing the local monitor is