ARCv2: Add explcit unaligned access support (and ability to disable too)

As of today we enable unaligned access unconditionally on ARCv2.
Do this under a Kconfig option to allow disable it for test, benchmarking
etc. Also while at it

  - Select HAVE_EFFICIENT_UNALIGNED_ACCESS
  - Although gcc defaults to unaligned access (since GNU 2018.03), add the
    right toggles for enabling or disabling as appropriate
  - update bootlog to prints both HW feature status (exists, enabled/disabled)
    and SW status (used / not used).
  - wire up the relaxed memcpy for unaligned access

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
[vgupta: squashed patches, handle gcc -mno-unaligned-access quick]

4 files changed, 26 insertions, 11 deletions

diff --git a/arch/arc/kernel/head.S b/arch/arc/kernel/head.S
index 30e090625916..36774348d23b 100644
--- a/arch/arc/kernel/head.S
+++ b/arch/arc/kernel/head.S
@@ -54,7 +54,12 @@
 	; gcc 7.3.1 (ARC GNU 2018.03) onwards generates unaligned access
 	; by default
 	lr	r5, [status32]
+#ifdef CONFIG_ARC_USE_UNALIGNED_MEM_ACCESS
 	bset	r5, r5, STATUS_AD_BIT
+#else
+	; Although disabled at reset, bootloader might have enabled it
+	bclr	r5, r5, STATUS_AD_BIT
+#endif
 	kflag	r5
 #endif
 .endm
diff --git a/arch/arc/kernel/intc-arcv2.c b/arch/arc/kernel/intc-arcv2.c
index cf18b3e5a934..c0d0124de089 100644
--- a/arch/arc/kernel/intc-arcv2.c
+++ b/arch/arc/kernel/intc-arcv2.c
@@ -95,7 +95,7 @@ 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));
 }
diff --git a/arch/arc/kernel/setup.c b/arch/arc/kernel/setup.c
index 7b2340996cf8..2266e4ee4142 100644
--- a/arch/arc/kernel/setup.c
+++ b/arch/arc/kernel/setup.c
@@ -263,7 +263,7 @@ static char *arc_cpu_mumbojumbo(int cpu_id, char *buf, int len)
 {
 	struct cpuinfo_arc *cpu = &cpuinfo_arc700[cpu_id];
 	struct bcr_identity *core = &cpu->core;
-	int i, n = 0, ua = 0;
+	int n = 0;
 
 	FIX_PTR(cpu);
 
@@ -283,16 +283,23 @@ static char *arc_cpu_mumbojumbo(int cpu_id, char *buf, int len)
 		       IS_AVAIL2(cpu->extn.rtc, "RTC [UP 64-bit] ", CONFIG_ARC_TIMERS_64BIT),
 		       IS_AVAIL2(cpu->extn.gfrc, "GFRC [SMP 64-bit] ", CONFIG_ARC_TIMERS_64BIT));
 
-#ifdef __ARC_UNALIGNED__
-	ua = 1;
+	n += scnprintf(buf + n, len - n, "%s%s%s%s%s%s",
+		       IS_AVAIL2(cpu->isa.atomic, "atomic ", CONFIG_ARC_HAS_LLSC),
+		       IS_AVAIL2(cpu->isa.ldd, "ll64 ", CONFIG_ARC_HAS_LL64),
+		       IS_AVAIL2(cpu->isa.unalign, "unalign ", CONFIG_ARC_USE_UNALIGNED_MEM_ACCESS));
+
+#if defined(__ARC_UNALIGNED__) && !defined(CONFIG_ARC_USE_UNALIGNED_MEM_ACCESS)
+	/*
+	 * gcc 7.3.1 (GNU 2018.03) onwards generate unaligned access by default
+	 * but -mno-unaligned-access to disable that didn't work until gcc 8.2.1
+	 * (GNU 2019.03). So landing here implies the interim period, when
+	 * despite Kconfig being off, gcc is generating unaligned accesses which
+	 * could bomb later on. So better to disallow such broken builds
+	 */
+	BUILD_BUG_ON_MSG(1, "gcc doesn't support -mno-unaligned-access");
 #endif
-	n += i = scnprintf(buf + n, len - n, "%s%s%s%s%s%s",
-			   IS_AVAIL2(cpu->isa.atomic, "atomic ", CONFIG_ARC_HAS_LLSC),
-			   IS_AVAIL2(cpu->isa.ldd, "ll64 ", CONFIG_ARC_HAS_LL64),
-			   IS_AVAIL1(cpu->isa.unalign, "unalign "), IS_USED_RUN(ua));
 
-	if (i)
-		n += scnprintf(buf + n, len - n, "\n\t\t: ");
+	n += scnprintf(buf + n, len - n, "\n\t\t: ");
 
 	if (cpu->extn_mpy.ver) {
 		if (cpu->extn_mpy.ver <= 0x2) {	/* ARCompact */
diff --git a/arch/arc/kernel/troubleshoot.c b/arch/arc/kernel/troubleshoot.c
index 215f515442e0..b0aa8c028331 100644
--- a/arch/arc/kernel/troubleshoot.c
+++ b/arch/arc/kernel/troubleshoot.c
@@ -145,7 +145,8 @@ static void show_ecr_verbose(struct pt_regs *regs)
 	} else if (vec == ECR_V_PROTV) {
 		if (cause_code == ECR_C_PROTV_INST_FETCH)
 			pr_cont("Execute from Non-exec Page\n");
-		else if (cause_code == ECR_C_PROTV_MISALIG_DATA)
+		else if (cause_code == ECR_C_PROTV_MISALIG_DATA &&
+		         IS_ENABLED(CONFIG_ISA_ARCOMPACT))
 			pr_cont("Misaligned r/w from 0x%08lx\n", address);
 		else
 			pr_cont("%s access not allowed on page\n",
@@ -161,6 +162,8 @@ static void show_ecr_verbose(struct pt_regs *regs)
 			pr_cont("Bus Error from Data Mem\n");
 		else
 			pr_cont("Bus Error, check PRM\n");
+	} else if (vec == ECR_V_MISALIGN) {
+		pr_cont("Misaligned r/w from 0x%08lx\n", address);
 #endif
 	} else if (vec == ECR_V_TRAP) {
 		if (regs->ecr_param == 5)