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]

1 files changed, 16 insertions, 9 deletions

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 */