riscv: cpu: Add callback to init each core

Add a callback harts_early_init() to start.S to allow different riscv
hart perform setup code for each hart as early as possible. Since all
the harts enter the callback, they must be able to run the same
setup.

Signed-off-by: Green Wan <green.wan@sifive.com>
Reviewed-by: Rick Chen <rick@andestech.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/riscv/cpu/cpu.c

@@ -140,3 +140,14 @@ int arch_early_init_r(void)
 {
 	return riscv_cpu_probe();
 }
+
+/**
+ * harts_early_init() - A callback function called by start.S to configure
+ * feature settings of each hart.
+ *
+ * In a multi-core system, memory access shall be careful here, it shall
+ * take care of race conditions.
+ */
+__weak void harts_early_init(void)
+{
+}

arch/riscv/cpu/start.S

@@ -117,6 +117,10 @@ call_board_init_f_0:
 	mv	sp, a0
 #endif
 
+	/* Configure proprietary settings and customized CSRs of harts */
+call_harts_early_init:
+	jal	harts_early_init
+
 #ifndef CONFIG_XIP
 	/*
 	 * Pick hart to initialize global data and run U-Boot. The other harts