RISC-V: Setup exception vector early

The trap vector is set only in trap_init which may be too late in some
cases. Early ioremap/efi spits many warning messages which may be useful.

Setup the trap vector early so that any warning/bug can be handled before
generic code invokes trap_init.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

Author: atishp04

arch/riscv/kernel/head.S

@@ -77,10 +77,16 @@ relocate:
 	csrw CSR_SATP, a0
 .align 2
 1:
-	/* Set trap vector to spin forever to help debug */
-	la a0, .Lsecondary_park
+	/* 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
+
 	/* Reload the global pointer */
 .option push
 .option norelax

arch/riscv/kernel/smpboot.c

@@ -154,10 +154,10 @@ asmlinkage __visible void smp_callin(void)
 	mmgrab(mm);
 	current->active_mm = mm;
 
-	trap_init();
 	notify_cpu_starting(curr_cpuid);
 	update_siblings_masks(curr_cpuid);
 	set_cpu_online(curr_cpuid, 1);
+
 	/*
 	 * Remote TLB flushes are ignored while the CPU is offline, so emit
 	 * a local TLB flush right now just in case.

arch/riscv/kernel/traps.c

@@ -174,13 +174,7 @@ int is_valid_bugaddr(unsigned long pc)
 }
 #endif /* CONFIG_GENERIC_BUG */
 
+/* stvec & scratch is already set from head.S */
 void trap_init(void)
 {
-	/*
-	 * Set sup0 scratch register to 0, indicating to exception vector
-	 * that we are presently executing in the kernel
-	 */
-	csr_write(CSR_SCRATCH, 0);
-	/* Set the exception vector address */
-	csr_write(CSR_TVEC, &handle_exception);
 }