arch: arc: fix the bug where firq comes out in user mode

firq's case is similar to regular irq, it also needs to consider
the case of reg bank switch.

Signed-off-by: Wayne Ren <[email protected]>

arch/arc/core/fast_irq.S

@@ -207,12 +207,36 @@ _firq_reschedule:
 	 * point, so when switching back to register bank 0, it will contain the
 	 * registers from the interrupted thread.
 	 */
-
+#if defined(CONFIG_USERSPACE)
+/* when USERSPACE is configured, here need to consider the case where firq comes
+ * out in user mode, according to ARCv2 ISA and nsim, the following micro ops
+ * will be executed:
+ *	sp<-reg bank1'sp
+ *      switch between sp and _ARC_V2_USER_SP
+ * then:
+ *      sp is the sp of kernel stack of interrupted thread
+ *      _ARC_V2_USER_SP is reg bank1'sp
+ *      the sp of user stack of interrupted thread is reg bank0'sp
+ * if firq comes out in kernel mode, the following micro ops will be executed:
+ *      sp<-reg bank'sp
+ * so, sw needs to do necessary handling to set up the correct sp
+ */
+	lr r0, [_ARC_V2_AUX_IRQ_ACT]
+	bbit0 r0, 31, _firq_from_kernel
+	aex sp, [_ARC_V2_USER_SP]
+	lr r0, [_ARC_V2_STATUS32]
+	and r0, r0, ~_ARC_V2_STATUS32_RB(7)
+	kflag r0
+	aex sp, [_ARC_V2_USER_SP]
+	b _firq_create_irq_stack_frame
+_firq_from_kernel:
+#endif
 	/* chose register bank #0 */
 	lr r0, [_ARC_V2_STATUS32]
 	and r0, r0, ~_ARC_V2_STATUS32_RB(7)
 	kflag r0
 
+_firq_create_irq_stack_frame:
 	/* we're back on the outgoing thread's stack */
 	_create_irq_stack_frame
 
@@ -225,6 +249,7 @@ _firq_reschedule:
 	st_s r0, [sp, ___isf_t_status32_OFFSET]
 
 	st ilink, [sp, ___isf_t_pc_OFFSET] /* ilink into pc */
+
 #ifdef CONFIG_SMP
 /*
  * load r0, r1 from irq stack
@@ -235,6 +260,16 @@ _firq_reschedule:
 #endif
 #endif
 
+#if defined(CONFIG_USERSPACE)
+/*
+ * need to remember the user/kernel status of interrupted thread, will be
+ * restored when thread switched back
+ */
+	lr r3, [_ARC_V2_AUX_IRQ_ACT]
+	and r3, r3, 0x80000000
+	push_s r3
+#endif
+
 #ifdef CONFIG_SMP
 	mov_s r2, r1
 #else
@@ -300,6 +335,16 @@ _firq_return_from_coop:
 _firq_return_from_rirq:
 _firq_return_from_firq:
 
+#if defined(CONFIG_USERSPACE)
+/*
+ * need to recover the user/kernel status of interrupted thread
+ */
+	pop_s r3
+	lr r2, [_ARC_V2_AUX_IRQ_ACT]
+	or r2, r2, r3
+	sr r2, [_ARC_V2_AUX_IRQ_ACT]
+#endif
+
 	_pop_irq_stack_frame
 
 	ld ilink, [sp, -4] /* status32 into ilink */