linux-kernel - [PATCH v2] riscv: Setup exception vector for nommu platform

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Date:   Thu, 13 Aug 2020 11:38:04 +0800
From:   Qiu Wenbo <qiuwenbo@...tium.com.cn>
To:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv@...ts.infradead.org
Cc:     Qiu Wenbo <qiuwenbo@...tium.com.cn>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup.patel@....com>,
        Atish Patra <atish.patra@....com>,
        Greentime Hu <greentime.hu@...ive.com>,
        Damien Le Moal <damien.lemoal@....com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] riscv: Setup exception vector for nommu platform

Exception vector is missing on nommu platform and that is an issue.
This patch is tested in Sipeed Maix Bit Dev Board.

Fixes: 79b1feba5455 ("RISC-V: Setup exception vector early")
Suggested-by: Anup Patel <anup@...infault.org>
Suggested-by: Atish Patra <atishp@...shpatra.org>
Signed-off-by: Qiu Wenbo <qiuwenbo@...tium.com.cn>
---
 arch/riscv/kernel/head.S | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index d0c5c316e9bb..0a4e81b8dc79 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -77,16 +77,10 @@ relocate:
 	csrw CSR_SATP, a0
 .align 2
 1:
-	/* Set trap vector to exception handler */
-	la a0, handle_exception
+	/* Set trap vector to spin forever to help debug */
+	la a0, .Lsecondary_park
 	csrw CSR_TVEC, a0
 
-	/*
-	 * Set sup0 scratch register to 0, indicating to exception vector that
-	 * we are presently executing in kernel.
-	 */
-	csrw CSR_SCRATCH, zero
-
 	/* Reload the global pointer */
 .option push
 .option norelax
@@ -144,9 +138,23 @@ secondary_start_common:
 	la a0, swapper_pg_dir
 	call relocate
 #endif
+	call setup_trap_vector
 	tail smp_callin
 #endif /* CONFIG_SMP */
 
+.align 2
+setup_trap_vector:
+	/* Set trap vector to exception handler */
+	la a0, handle_exception
+	csrw CSR_TVEC, a0
+
+	/*
+	 * Set sup0 scratch register to 0, indicating to exception vector that
+	 * we are presently executing in kernel.
+	 */
+	csrw CSR_SCRATCH, zero
+	ret
+
 .Lsecondary_park:
 	/* We lack SMP support or have too many harts, so park this hart */
 	wfi
@@ -240,6 +248,7 @@ clear_bss_done:
 	call relocate
 #endif /* CONFIG_MMU */
 
+	call setup_trap_vector
 	/* Restore C environment */
 	la tp, init_task
 	sw zero, TASK_TI_CPU(tp)
-- 
2.28.0