Hi Rick,

On Fri, 2019-02-15 at 14:51 +0800, Rick Chen wrote:

Hi Lukas

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From: Lukas Auer [mailto:lukas.auer@aisec.fraunhofer.de] Sent: Tuesday, February 12, 2019 6:14 AM To: u-boot@lists.denx.de Cc: Atish Patra; Anup Patel; Bin Meng; Andreas Schwab; Palmer Dabbelt; Alexander Graf; Lukas Auer; Anup Patel; Rick Jian-Zhi Chen(陳建志); Baruch Siach; Stefan Roese Subject: [PATCH 5/7] 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. A new config option, CONFIG_MAIN_HART, is used to select 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

arch/riscv/Kconfig | 12 +++++ arch/riscv/cpu/start.S | 102 ++++++++++++++++++++++++++++++++++- arch/riscv/include/asm/csr.h | 1 + 3 files changed, 114 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 3a51339c4d..af8d0f8d67 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -140,4 +140,16 @@ config SBI_IPI default y if RISCV_SMODE depends on SMP

+config MAIN_HART

• int "Main hart in system"
  

• default 0
  

• help
  

•   Some SoCs include harts of various sizes, some of which
  

might not

•   be suitable for running U-Boot. CONFIG_MAIN_HART is used
  

to select

•   the hart U-Boot runs on.
  

+config STACK_SIZE_SHIFT

• int
  

• default 13
  

endmenu diff --git a/arch/riscv/cpu/start.S b/arch/riscv/cpu/start.S index a30f6f7194..ce7230df37 100644 --- a/arch/riscv/cpu/start.S +++ b/arch/riscv/cpu/start.S @@ -13,6 +13,7 @@ #include <config.h> #include <common.h> #include <elf.h> +#include <asm/csr.h> #include <asm/encoding.h> #include <generated/asm-offsets.h>

If u-boot boot from flash by itself in M-mode without any FSBL or gdb, in this case there will be no chance to assign a0. Can we add some code as below :

_start: +#ifdef CONFIG_RISCV_MMODE

•   csrr    a0, mhartid
  

+#endif /* save hart id and dtb pointer */ mv s0, a0 mv s1, a1

How do you think about it ?

Good point, thanks! Even without SMP support this could cause issues if we pass an invalid hart ID to Linux. I will add a patch for this.

Thanks, Lukas

Thanks Rick

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@@ -45,6 +46,23 @@ _start: /* mask all interrupts */ csrw MODE_PREFIX(ie), zero

+#ifdef CONFIG_SMP

• /* check if hart is within range */
  

• /* s0: hart id */
  

• li      t0, CONFIG_NR_CPUS
  

• bge     s0, t0, hart_out_of_bounds_loop
  

+#endif