[PATCH 1/3] ARC: allow to overide default mcpu compiler flag

[Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>]

By default we set -mcpu=xxx compiler flag depending on the CPU ISA
version. It's good starting point, however that may be not enough
as for some platforms we may want to use some specific 'mcpu'
options for better optimization or to workaround HW issues.

We are going to use this option for HSDK-4xD board support.
In addition it also allows to awoid patching 'mcpu' in ARC Makefile
when we building Linux for some non-standard simulation or FPGA-based
platforms.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
---
 arch/arc/Kconfig  | 7 +++++++
 arch/arc/Makefile | 4 ++++
 2 files changed, 11 insertions(+)

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index ff306246d0f8..2d4f85dc914e 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -377,6 +377,13 @@ config ARC_HAS_SWAPE
 	bool "Insn: SWAPE (endian-swap)"
 	default y
 
+config ARC_TUNE_MCPU
+	string "Overide default -mcpu compiler flag"
+	default ""
+	help
+	  Overide default -mcpu=xxx compiler flag (which is set depending on
+	  the ISA version) with the specified value.
+
 if ISA_ARCV2
 
 config ARC_USE_UNALIGNED_MEM_ACCESS
diff --git a/arch/arc/Makefile b/arch/arc/Makefile
index 20e9ab6cc521..eb88ba5b1573 100644
--- a/arch/arc/Makefile
+++ b/arch/arc/Makefile
@@ -10,8 +10,12 @@ CROSS_COMPILE := $(call cc-cross-prefix, arc-linux- arceb-linux-)
 endif
 
 cflags-y	+= -fno-common -pipe -fno-builtin -mmedium-calls -D__linux__
+ifeq ($(CONFIG_ARC_TUNE_MCPU),"")
 cflags-$(CONFIG_ISA_ARCOMPACT)	+= -mA7
 cflags-$(CONFIG_ISA_ARCV2)	+= -mcpu=hs38
+else
+cflags-y			+= $(shell echo $(CONFIG_ARC_TUNE_MCPU))
+endif
 
 ifdef CONFIG_ARC_CURR_IN_REG
 # For a global register defintion, make sure it gets passed to every file
-- 
2.21.3