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>
diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S
index 2fdf867..0d91ca0 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