[RFC PATCH v4 1/2] arch: riscv: cpu: Add callback to init each core

[Green Wan]

Add a callback riscv_hart_early_init() to ./arch/riscv/cpu/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 at sifive.com>
---
 arch/riscv/cpu/cpu.c   | 15 +++++++++++++++
 arch/riscv/cpu/start.S | 14 ++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
index 85592f5bee..1652e51137 100644
--- a/arch/riscv/cpu/cpu.c
+++ b/arch/riscv/cpu/cpu.c
@@ -140,3 +140,18 @@ int arch_early_init_r(void)
 {
 	return riscv_cpu_probe();
 }
+
+/**
+ * riscv_hart_early_init() - A dummy function called by
+ * ./arch/riscv/cpu/start.S to allow to disable/enable features of each core.
+ * For example, turn on or off the functional block of CPU harts.
+ *
+ * In a multi-core system, this function must not access shared resources.
+ *
+ * Any access to such resources would probably be better done with
+ * available_harts_lock held. However, I doubt that any such access will be
+ * necessary.
+ */
+__weak void riscv_hart_early_init(void)
+{
+}
diff --git a/arch/riscv/cpu/start.S b/arch/riscv/cpu/start.S
index 8589509e01..ab73008f23 100644
--- a/arch/riscv/cpu/start.S
+++ b/arch/riscv/cpu/start.S
@@ -117,6 +117,20 @@ call_board_init_f_0:
 	mv	sp, a0
 #endif
 
+#if CONFIG_IS_ENABLED(RISCV_MMODE)
+	/*
+	 * Jump to riscv_hart_early_init() to perform init for each core. Not
+	 * expect to access gd since gd is not initialized. All operations in the
+	 * function should affect core itself only. In multi-core system, any access
+	 * to common resource or registers outside core should be avoided or need a
+	 * protection for multicore.
+	 *
+	 * A dummy implementation is provided in ./arch/riscv/cpu/cpu.c.
+	 */
+call_riscv_hart_early_init:
+	jal	riscv_hart_early_init
+#endif
+
 #ifndef CONFIG_XIP
 	/*
 	 * Pick hart to initialize global data and run U-Boot. The other harts
-- 
2.31.0