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Subject[PATCH 10/17] riscv: read the hart ID from mhartid on boot
Date
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>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
arch/riscv/kernel/head.S | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index e5fa5481aa99..a4c170e41a34 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -18,6 +18,14 @@ ENTRY(_start)
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, mhartid
+#endif
+
/* Load the global pointer */
.option push
.option norelax
--
2.20.1
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