From accb9dbc4affdb7ebf30db7e9ba71eee47280081 Mon Sep 17 00:00:00 2001
From: Damien Le Moal
Date: Mon, 28 Oct 2019 13:10:39 +0100
Subject: riscv: read the hart ID from mhartid on boot

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>---
 arch/riscv/kernel/head.S | 8 ++++++++
 1 file changed, 8 insertions(+)

(limited to 'arch/riscv/kernel/head.S')

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
-- 
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