Messages in this thread Patch in this message | | | From | Christoph Hellwig <> | Subject | [PATCH 08/12] riscv: read the hart ID from mhartid on boot | Date | Mon, 28 Oct 2019 13:10:39 +0100 |
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From: Damien Le Moal <damien.lemoal@wdc.com>
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 <damien.lemoal@wdc.com> Reviewed-by: Anup Patel <anup@brainfault.org> Reviewed-by: Atish Patra <atish.patra@wdc.com> Signed-off-by: Christoph Hellwig <hch@lst.de> --- 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 0ab642811028..318192c66fd8 100644 --- a/arch/riscv/include/asm/csr.h +++ b/arch/riscv/include/asm/csr.h @@ -99,6 +99,7 @@ #define CSR_MCAUSE 0x342 #define CSR_MTVAL 0x343 #define CSR_MIP 0x344 +#define CSR_MHARTID 0xf14 #ifdef CONFIG_RISCV_M_MODE # define CSR_STATUS CSR_MSTATUS diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S index 5cfd2c582945..fc9973086946 100644 --- a/arch/riscv/kernel/head.S +++ b/arch/riscv/kernel/head.S @@ -50,6 +50,14 @@ _start_kernel: csrw CSR_IE, zero csrw CSR_IP, zero +#ifdef CONFIG_RISCV_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
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