[RFC PATCH v6 2/2] arch: riscv: cpu: fu740: 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>
Reviewed-by: Bin Meng <bmeng.cn at gmail.com>
---
 arch/riscv/cpu/fu740/spl.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/riscv/cpu/fu740/spl.c b/arch/riscv/cpu/fu740/spl.c
index ea0b2283a2..55e30346ff 100644
--- a/arch/riscv/cpu/fu740/spl.c
+++ b/arch/riscv/cpu/fu740/spl.c
@@ -6,6 +6,9 @@
 
 #include <dm.h>
 #include <log.h>
+#include <asm/csr.h>
+
+#define CSR_U74_FEATURE_DISABLE	0x7c1
 
 int spl_soc_init(void)
 {
@@ -21,3 +24,15 @@ int spl_soc_init(void)
 
 	return 0;
 }
+
+void harts_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);
+}
-- 
2.31.0