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riscv: read the hart ID from mhartid on boot

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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>
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
This commit is contained in:
Damien Le Moal 2019-10-28 13:10:39 +01:00 committed by Paul Walmsley
parent fcdc653751
commit accb9dbc4a
2 changed files with 9 additions and 0 deletions
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1
arch/riscv/include/asm/csr.h
View File

@ -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

8
arch/riscv/kernel/head.S
View File

@ -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