riscv: Enable LOCKDEP_SUPPORT & fixup TRACE_IRQFLAGS_SUPPORT

Lockdep is needed by proving the spinlocks and rwlocks. To suupport
it, we need fixup TRACE_IRQFLAGS_SUPPORT in kernel/entry.S. This
patch follow Documentation/irqflags-tracing.txt.
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Kconfig

@@ -179,6 +179,9 @@ config PGTABLE_LEVELS
 	default 3 if 64BIT
 	default 2
 
+config LOCKDEP_SUPPORT
+	def_bool y
+
 source "arch/riscv/Kconfig.socs"
 
 menu "Platform type"

arch/riscv/kernel/entry.S

@@ -97,19 +97,26 @@ _save_context:
 	la gp, __global_pointer$
 .option pop
 
-	la ra, ret_from_exception
+#ifdef CONFIG_TRACE_IRQFLAGS
+	call trace_hardirqs_off
+#endif
 	/*
 	 * MSB of cause differentiates between
 	 * interrupts and exceptions
 	 */
 	bge s4, zero, 1f
 
+	la ra, ret_from_exception
+
 	/* Handle interrupts */
 	move a0, sp /* pt_regs */
 	la a1, handle_arch_irq
 	REG_L a1, (a1)
 	jr a1
 1:
+#ifdef CONFIG_TRACE_IRQFLAGS
+	call trace_hardirqs_on
+#endif
 	/*
 	 * Exceptions run with interrupts enabled or disabled depending on the
 	 * state of SR_PIE in m/sstatus.
@@ -119,6 +126,7 @@ _save_context:
 	csrs CSR_STATUS, SR_IE
 
 1:
+	la ra, ret_from_exception
 	/* Handle syscalls */
 	li t0, EXC_SYSCALL
 	beq s4, t0, handle_syscall
@@ -137,6 +145,17 @@ _save_context:
 	tail do_trap_unknown
 
 handle_syscall:
+#ifdef CONFIG_TRACE_IRQFLAGS
+	/* Recover a0 - a7 for system calls */
+	REG_L a0, PT_A0(sp)
+	REG_L a1, PT_A1(sp)
+	REG_L a2, PT_A2(sp)
+	REG_L a3, PT_A3(sp)
+	REG_L a4, PT_A4(sp)
+	REG_L a5, PT_A5(sp)
+	REG_L a6, PT_A6(sp)
+	REG_L a7, PT_A7(sp)
+#endif
 	 /* save the initial A0 value (needed in signal handlers) */
 	REG_S a0, PT_ORIG_A0(sp)
 	/*
@@ -190,6 +209,9 @@ ret_from_syscall_rejected:
 ret_from_exception:
 	REG_L s0, PT_STATUS(sp)
 	csrc CSR_STATUS, SR_IE
+#ifdef CONFIG_TRACE_IRQFLAGS
+	call trace_hardirqs_off
+#endif
 #ifdef CONFIG_RISCV_M_MODE
 	/* the MPP value is too large to be used as an immediate arg for addi */
 	li t0, SR_MPP
@@ -216,6 +238,16 @@ resume_userspace:
 	csrw CSR_SCRATCH, tp
 
 restore_all:
+#ifdef CONFIG_TRACE_IRQFLAGS
+	REG_L s1, PT_STATUS(sp)
+	andi t0, s1, SR_PIE
+	beqz t0, 1f
+	call trace_hardirqs_on
+	j 2f
+1:
+	call trace_hardirqs_off
+2:
+#endif
 	REG_L a0, PT_STATUS(sp)
 	/*
 	 * The current load reservation is effectively part of the processor's