[U-Boot] [PATCH v2 09/20] riscv: Implement riscv_get_time() API using rdtime instruction

[Bin Meng]

From: Anup Patel <anup at brainfault.org>

This adds an implementation of riscv_get_time() API that is using
rdtime instruction.

This is the case for S-mode U-Boot, and is useful for processors
that support rdtime in M-mode too.

Signed-off-by: Anup Patel <anup at brainfault.org>
Signed-off-by: Bin Meng <bmeng.cn at gmail.com>

---

Changes in v2:
- incorporated and reworked Anup's S-mode timer patch
  @ http://patchwork.ozlabs.org/patch/1006663/

 arch/riscv/Kconfig      |  8 ++++++++
 arch/riscv/lib/Makefile |  1 +
 arch/riscv/lib/rdtime.c | 36 ++++++++++++++++++++++++++++++++++++
 3 files changed, 45 insertions(+)
 create mode 100644 arch/riscv/lib/rdtime.c

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index f513f52..7dc6e3f 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -104,4 +104,12 @@ config SIFIVE_CLINT
 	  The SiFive CLINT block holds memory-mapped control and status registers
 	  associated with software and timer interrupts.
 
+config RISCV_RDTIME
+	bool
+	default y if RISCV_SMODE
+	help
+	  The provides the riscv_get_time() API that is implemented using the
+	  standard rdtime instruction. This is the case for S-mode U-Boot, and
+	  is useful for processors that support rdtime in M-mode too.
+
 endmenu
diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
index b13c876..edfa616 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -9,6 +9,7 @@
 obj-$(CONFIG_CMD_BOOTM) += bootm.o
 obj-$(CONFIG_CMD_GO) += boot.o
 obj-y	+= cache.o
+obj-$(CONFIG_RISCV_RDTIME) += rdtime.o
 obj-$(CONFIG_SIFIVE_CLINT) += sifive_clint.o
 obj-y	+= interrupts.o
 obj-y	+= reset.o
diff --git a/arch/riscv/lib/rdtime.c b/arch/riscv/lib/rdtime.c
new file mode 100644
index 0000000..b16680f
--- /dev/null
+++ b/arch/riscv/lib/rdtime.c
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2018, Anup Patel <anup at brainfault.org>
+ * Copyright (C) 2018, Bin Meng <bmeng.cn at gmail.com>
+ *
+ * The riscv_get_time() API implementation that is using the
+ * standard rdtime instruction.
+ */
+
+#include <common.h>
+
+/* Implement the API required by RISC-V timer driver */
+u64 riscv_get_time(void)
+{
+#ifdef CONFIG_64BIT
+	u64 n;
+
+	__asm__ __volatile__ (
+		"rdtime %0"
+		: "=r" (n));
+
+	return n;
+#else
+	u32 lo, hi, tmp;
+
+	__asm__ __volatile__ (
+		"1:\n"
+		"rdtimeh %0\n"
+		"rdtime %1\n"
+		"rdtimeh %2\n"
+		"bne %0, %2, 1b"
+		: "=&r" (hi), "=&r" (lo), "=&r" (tmp));
+
+	return ((u64)hi << 32) | lo;
+#endif
+}
-- 
2.7.4