[PATCH v2 2/5] ARCv2: introduce unaligned access under a Kconfig option

[Eugeniy Paltsev]

As of today we enable unaligned access unconditionally on ARCv2.
Lets move it under Kconfig option so we can disable it in case of
using HW configuration which lacks of it.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@xxxxxxxxxxxx>
---
 arch/arc/Kconfig                      |  8 ++++++++
 arch/arc/include/asm/irqflags-arcv2.h |  4 ++++
 arch/arc/kernel/head.S                | 14 +++++++++-----
 arch/arc/kernel/intc-arcv2.c          |  2 +-
 4 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 376366a7db81..37c8aeefa3a5 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -387,6 +387,14 @@ config ARC_HAS_SWAPE
 
 if ISA_ARCV2
 
+config ARC_USE_UNALIGNED_MEM_ACCESS
+	bool "Handle unaligned access in HW and use it"
+	default y
+	help
+	  The ARC HS architecture supports unaligned memory access
+	  which is disabled by default. Enable unaligned access in
+	  hardware and use it in software.
+
 config ARC_HAS_LL64
 	bool "Insn: 64bit LDD/STD"
 	help
diff --git a/arch/arc/include/asm/irqflags-arcv2.h b/arch/arc/include/asm/irqflags-arcv2.h
index 8a4f77ea3238..9b911e2c6b31 100644
--- a/arch/arc/include/asm/irqflags-arcv2.h
+++ b/arch/arc/include/asm/irqflags-arcv2.h
@@ -44,8 +44,12 @@
 #define ARCV2_IRQ_DEF_PRIO	1
 
 /* seed value for status register */
+#ifdef CONFIG_ARC_USE_UNALIGNED_MEM_ACCESS
 #define ISA_INIT_STATUS_BITS	(STATUS_IE_MASK | STATUS_AD_MASK | \
 					(ARCV2_IRQ_DEF_PRIO << 1))
+#else
+#define ISA_INIT_STATUS_BITS	(STATUS_IE_MASK | (ARCV2_IRQ_DEF_PRIO << 1))
+#endif /* CONFIG_ARC_USE_UNALIGNED_MEM_ACCESS */
 
 #ifndef __ASSEMBLY__
 
diff --git a/arch/arc/kernel/head.S b/arch/arc/kernel/head.S
index 25b3a247e11c..bd24ba0e0264 100644
--- a/arch/arc/kernel/head.S
+++ b/arch/arc/kernel/head.S
@@ -49,11 +49,15 @@
 
 1:
 
-#ifdef CONFIG_ISA_ARCV2
-	; Enable unaligned access as disabled by default in hw while
-	; gcc 8.1.0 onwards (ARC GNU 2018.03) unconditionally generates
-	; code for unaligned accesses
-	flag    1 << STATUS_AD_BIT
+	; Enable / disable HW handling of unaligned access in the CPU.
+#ifdef CONFIG_ARC_USE_UNALIGNED_MEM_ACCESS
+	kflag	STATUS_AD_MASK
+#else
+	; Handling of unaligned access is disabled by default but we disable it
+	; manually in case of any bootloader enabled it earlier.
+	lr	r5, [ARC_REG_STATUS32]
+	bclr	r5, r5, STATUS_AD_BIT
+	kflag	r5
 #endif
 .endm
 
diff --git a/arch/arc/kernel/intc-arcv2.c b/arch/arc/kernel/intc-arcv2.c
index 067ea362fb3e..6359896da1ea 100644
--- a/arch/arc/kernel/intc-arcv2.c
+++ b/arch/arc/kernel/intc-arcv2.c
@@ -93,7 +93,7 @@ void arc_init_IRQ(void)
 
 	/* setup status32, don't enable intr yet as kernel doesn't want */
 	tmp = read_aux_reg(ARC_REG_STATUS32);
-	tmp |= STATUS_AD_MASK | (ARCV2_IRQ_DEF_PRIO << 1);
+	tmp |= ARCV2_IRQ_DEF_PRIO << 1;
 	tmp &= ~STATUS_IE_MASK;
 	asm volatile("kflag %0	\n"::"r"(tmp));
 }
-- 
2.14.5