riscv: add support for multi-hart systems

On RISC-V, all harts boot independently. To be able to run on a
multi-hart system, U-Boot must be extended with the functionality to
manage all harts in the system. All harts entering U-Boot are registered
in the available_harts mask stored in global data. A hart lottery system
as used in the Linux kernel selects the hart U-Boot runs on. All other
harts are halted. U-Boot can delegate functions to them using
smp_call_function().

Every hart has a valid pointer to the global data structure and a 8KiB
stack by default. The stack size is set with CONFIG_STACK_SIZE_SHIFT.

Signed-off-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
index e662140427a..c32de8a4c3e 100644
--- a/arch/riscv/cpu/cpu.c
+++ b/arch/riscv/cpu/cpu.c
@@ -12,10 +12,17 @@
 #include <dm/uclass-internal.h>
 
 /*
- * prior_stage_fdt_address must be stored in the data section since it is used
+ * The variables here must be stored in the data section since they are used
  * before the bss section is available.
  */
 phys_addr_t prior_stage_fdt_address __attribute__((section(".data")));
+u32 hart_lottery __attribute__((section(".data"))) = 0;
+
+/*
+ * The main hart running U-Boot has acquired available_harts_lock until it has
+ * finished initialization of global data.
+ */
+u32 available_harts_lock = 1;
 
 static inline bool supports_extension(char ext)
 {