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[3.16-stable,14/14] ARM: 8452/3: PJ4: make coprocessor access sequences buildable in Thumb2 mode

Message ID 20170509100502.1358298-15-arnd@arndb.de
State New
Headers show
Series [3.16-stable,01/14] staging: r8192ee: prorperly format warning message | expand

Commit Message

Arnd Bergmann May 9, 2017, 10:05 a.m. UTC 
From: Ard Biesheuvel <ard.biesheuvel@linaro.org>


Commit 5008efc83bf85b647aa1cbc44718b1675bbb7444 upstream.

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>

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

---
 arch/arm/kernel/Makefile  | 1 -
 arch/arm/kernel/pj4-cp0.c | 4 ++++
 2 files changed, 4 insertions(+), 1 deletion(-)

-- 
2.9.0
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Patch

diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 2ecc7d15bc09..03120e656aea 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -84,7 +84,6 @@  obj-$(CONFIG_CPU_PJ4B)		+= pj4-cp0.o
 obj-$(CONFIG_IWMMXT)		+= iwmmxt.o
 obj-$(CONFIG_PERF_EVENTS)	+= perf_regs.o
 obj-$(CONFIG_HW_PERF_EVENTS)	+= perf_event.o perf_event_cpu.o
-CFLAGS_pj4-cp0.o		:= -marm
 AFLAGS_iwmmxt.o			:= -Wa,-mcpu=iwmmxt
 obj-$(CONFIG_ARM_CPU_TOPOLOGY)  += topology.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));
 }