From: Damien Le Moal <[email protected]> When in M-Mode, we can use the mhartid CSR to get the ID of the running HART. Doing so, direct M-Mode boot without firmware is possible.
Signed-off-by: Damien Le Moal <[email protected]> Signed-off-by: Christoph Hellwig <[email protected]> Reviewed-by: Atish Patra <[email protected]> --- arch/riscv/include/asm/csr.h | 1 + arch/riscv/kernel/head.S | 8 ++++++++ 2 files changed, 9 insertions(+) diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h index 53d7ce74b447..64f8fe84b88f 100644 --- a/arch/riscv/include/asm/csr.h +++ b/arch/riscv/include/asm/csr.h @@ -81,6 +81,7 @@ #define SIE_SEIE (_AC(0x1, UL) << IRQ_S_EXT) /* symbolic CSR names: */ +#define CSR_MHARTID 0xf14 #define CSR_MSTATUS 0x300 #define CSR_MIE 0x304 #define CSR_MTVEC 0x305 diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S index bb96bb7b95d2..275c2ab1e990 100644 --- a/arch/riscv/kernel/head.S +++ b/arch/riscv/kernel/head.S @@ -50,6 +50,14 @@ _start_kernel: csrw CSR_XIE, zero csrw CSR_XIP, zero +#ifdef CONFIG_M_MODE + /* + * The hartid in a0 is expected later on, and we have no firmware + * to hand it to us. + */ + csrr a0, CSR_MHARTID +#endif + /* Load the global pointer */ .option push .option norelax -- 2.20.1
