feat(trbe): enable access to trace buffer control registers from lower NS EL
Introduced a build flag 'ENABLE_TRBE_FOR_NS' to enable trace buffer
control registers access in NS-EL2, or NS-EL1 (when NS-EL2 is
implemented but unused).
Change-Id: I285a672ccd395eebd377714c992bb21062a729cc
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
diff --git a/lib/extensions/trbe/trbe.c b/lib/extensions/trbe/trbe.c
new file mode 100644
index 0000000..9f754d5
--- /dev/null
+++ b/lib/extensions/trbe/trbe.c
@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2021, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <arch.h>
+#include <arch_helpers.h>
+#include <lib/el3_runtime/pubsub.h>
+#include <lib/extensions/trbe.h>
+
+static void tsb_csync(void)
+{
+ /*
+ * The assembler does not yet understand the tsb csync mnemonic
+ * so use the equivalent hint instruction.
+ */
+ __asm__ volatile("hint #18");
+}
+
+static bool trbe_supported(void)
+{
+ uint64_t features;
+
+ features = read_id_aa64dfr0_el1() >> ID_AA64DFR0_TRACEBUFFER_SHIFT;
+ return ((features & ID_AA64DFR0_TRACEBUFFER_MASK) ==
+ ID_AA64DFR0_TRACEBUFFER_SUPPORTED);
+}
+
+void trbe_enable(void)
+{
+ uint64_t val;
+
+ if (trbe_supported()) {
+ /*
+ * MDCR_EL3.NSTB = 0b11
+ * Allow access of trace buffer control registers from NS-EL1
+ * and NS-EL2, tracing is prohibited in Secure and Realm state
+ * (if implemented).
+ */
+ val = read_mdcr_el3();
+ val |= MDCR_NSTB(MDCR_NSTB_EL1);
+ write_mdcr_el3(val);
+ }
+}
+
+static void *trbe_drain_trace_buffers_hook(const void *arg __unused)
+{
+ if (trbe_supported()) {
+ /*
+ * Before switching from normal world to secure world
+ * the trace buffers need to be drained out to memory. This is
+ * required to avoid an invalid memory access when TTBR is switched
+ * for entry to S-EL1.
+ */
+ tsb_csync();
+ dsbnsh();
+ }
+
+ return (void *)0;
+}
+
+SUBSCRIBE_TO_EVENT(cm_entering_secure_world, trbe_drain_trace_buffers_hook);