[RFC PATCH v4 2/2] board: sifive: unmatched: clear feature disable CSR

[Green Wan]

Clear feature disable CSR to turn on all features of hart. The detail
is specified at section, 'SiFive Feature Disable CSR', in user manual

https://sifive.cdn.prismic.io/sifive/aee0dd4c-d156-496e-a6c4-db0cf54bbe68_sifive_U74MC_rtl_full_20G1.03.00_manual.pdf

Signed-off-by: Green Wan <green.wan at sifive.com>
Reviewed-by: Sean Anderson <seanga2 at gmail.com>
---
 board/sifive/unmatched/spl.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/board/sifive/unmatched/spl.c b/board/sifive/unmatched/spl.c
index 5e1333b09a..2af3069b55 100644
--- a/board/sifive/unmatched/spl.c
+++ b/board/sifive/unmatched/spl.c
@@ -12,6 +12,7 @@
 #include <log.h>
 #include <linux/delay.h>
 #include <linux/io.h>
+#include <asm/csr.h>
 #include <asm/gpio.h>
 #include <asm/arch/gpio.h>
 #include <asm/arch/spl.h>
@@ -22,6 +23,20 @@
 #define MODE_SELECT_SD		0xb
 #define MODE_SELECT_MASK	GENMASK(3, 0)
 
+#define CSR_U74_FEATURE_DISABLE	0x7c1
+
+void riscv_hart_early_init(void)
+{
+	/*
+	 * Feature Disable CSR
+	 *
+	 * Clear feature disable CSR to '0' to turn on all features for
+	 * each core. This operation must be in m-mode.
+	 */
+	if (CONFIG_IS_ENABLED(RISCV_MMODE))
+		csr_write(CSR_U74_FEATURE_DISABLE, 0);
+}
+
 int spl_board_init_f(void)
 {
 	int ret;
-- 
2.31.0