From mboxrd@z Thu Jan 1 00:00:00 1970 From: ard.biesheuvel@linaro.org (Ard Biesheuvel) Date: Thu, 17 Dec 2015 16:25:12 +0100 Subject: [PATCH] ARM: PJ4: make coprocessor access sequences buildable in Thumb2 mode Message-ID: <1450365912-3834-1-git-send-email-ard.biesheuvel@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. Unlike Xscale, where this code originated, PJ4 is strictly ARMv7 so this should always be supported. Signed-off-by: Ard Biesheuvel --- arch/arm/kernel/Makefile | 1 - arch/arm/kernel/pj4-cp0.c | 10 +++------- 2 files changed, 3 insertions(+), 8 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..a311977d795d 100644 --- a/arch/arm/kernel/pj4-cp0.c +++ b/arch/arm/kernel/pj4-cp0.c @@ -62,14 +62,10 @@ static u32 __init pj4_cp_access_read(void) static void __init pj4_cp_access_write(u32 value) { - u32 temp; - __asm__ __volatile__ ( - "mcr p15, 0, %1, c1, c0, 2\n\t" - "mrc p15, 0, %0, c1, c0, 2\n\t" - "mov %0, %0\n\t" - "sub pc, pc, #4\n\t" - : "=r" (temp) : "r" (value)); + "mcr p15, 0, %0, c1, c0, 2\n\t" + "isb\n\t" + : : "r" (value)); } static int __init pj4_get_iwmmxt_version(void) -- 2.5.0