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>

2 files changed, 4 insertions, 1 deletions

diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index af9e59bf3831..3c789496297f 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -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
diff --git a/arch/arm/kernel/pj4-cp0.c b/arch/arm/kernel/pj4-cp0.c
index 8153e36b2491..7c9248b74d3f 100644
--- a/arch/arm/kernel/pj4-cp0.c
+++ b/arch/arm/kernel/pj4-cp0.c
@@ -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));
 }