Commit 5008efc8 authored Dec 22, 2015 by Ard Biesheuvel Committed by Russell King Jan 04, 2016

ARM: 8452/3: PJ4: make coprocessor access sequences buildable in Thumb2 mode



The PJ4 inline asm sequence to write to cp15 cannot be built in Thumb-2
mode, due to the way it performs arithmetic on the program counter, so it
is built in ARM mode instead. However, building C files in ARM mode under
CONFIG_THUMB2_KERNEL is problematic, since the instrumentation performed
by subsystems like ftrace does not expect having to deal with interworking
branches.

Since the sequence in question is simply a poor man's ISB instruction,
let's use a straight 'isb' instead when building in Thumb2 mode. Thumb2
implies V7, so 'isb' should always be supported in that case.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

parent 36f46d6d

arch/arm/kernel/Makefile

+0 −1

Original line number	Diff line number	Diff line
		@@ -73,7 +73,6 @@ obj-$(CONFIG_IWMMXT) += iwmmxt.o
		obj-$(CONFIG_PERF_EVENTS) += perf_regs.o perf_callchain.o
		obj-$(CONFIG_HW_PERF_EVENTS) += perf_event_xscale.o perf_event_v6.o \
		perf_event_v7.o
		CFLAGS_pj4-cp0.o := -marm
		AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt
		obj-$(CONFIG_ARM_CPU_TOPOLOGY) += topology.o
		obj-$(CONFIG_VDSO) += vdso.o

arch/arm/kernel/pj4-cp0.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -66,9 +66,13 @@ static void __init pj4_cp_access_write(u32 value)

		__asm__ __volatile__ (
		"mcr p15, 0, %1, c1, c0, 2\n\t"
		#ifdef CONFIG_THUMB2_KERNEL
		"isb\n\t"
		#else
		"mrc p15, 0, %0, c1, c0, 2\n\t"
		"mov %0, %0\n\t"
		"sub pc, pc, #4\n\t"
		#endif
		: "=r" (temp) : "r" (value));
		}

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