Hexagon: add support for single-stepping (v4+)

Hardware single-step is only available on v4 and later
architectures.
Signed-off-by: Richard Kuo <rkuo@codeaurora.org>

arch/hexagon/include/uapi/asm/ptrace.h

@@ -36,4 +36,9 @@ extern const char *regs_query_register_name(unsigned int offset);
 	((struct pt_regs *) \
 	 ((unsigned long)current_thread_info() + THREAD_SIZE) - 1)
 
+#if CONFIG_HEXAGON_ARCH_VERSION >= 4
+#define arch_has_single_step()	(1)
+#endif
+
+
 #endif

arch/hexagon/include/uapi/asm/registers.h

@@ -211,6 +211,9 @@ struct pt_regs {
 #define pt_psp(regs) ((regs)->hvmer.vmpsp)
 #define pt_badva(regs) ((regs)->hvmer.vmbadva)
 
+#define pt_set_singlestep(regs) ((regs)->hvmer.vmest |= (1<<HVM_VMEST_SS_SFT))
+#define pt_clr_singlestep(regs) ((regs)->hvmer.vmest &= ~(1<<HVM_VMEST_SS_SFT))
+
 #define pt_set_rte_sp(regs, sp) do {\
 	pt_psp(regs) = (sp);\
 	(regs)->SP = (unsigned long) &((regs)->hvmer);\

arch/hexagon/kernel/ptrace.c

@@ -32,6 +32,21 @@
 
 #include <asm/user.h>
 
+#if arch_has_single_step()
+/*  Both called from ptrace_resume  */
+void user_enable_single_step(struct task_struct *child)
+{
+	pt_set_singlestep(task_pt_regs(child));
+	set_tsk_thread_flag(child, TIF_SINGLESTEP);
+}
+
+void user_disable_single_step(struct task_struct *child)
+{
+	pt_clr_singlestep(task_pt_regs(child));
+	clear_tsk_thread_flag(child, TIF_SINGLESTEP);
+}
+#endif
+
 static int genregs_get(struct task_struct *target,
 		   const struct user_regset *regset,
 		   unsigned int pos, unsigned int count,

arch/hexagon/kernel/traps.c

@@ -451,3 +451,14 @@ void do_machcheck(struct pt_regs *regs)
 	/* Halt and catch fire */
 	__vmstop();
 }
+
+/*
+ * Treat this like the old 0xdb trap.
+ */
+
+void do_debug_exception(struct pt_regs *regs)
+{
+	regs->hvmer.vmest &= ~HVM_VMEST_CAUSE_MSK;
+	regs->hvmer.vmest |= (TRAP_DEBUG << HVM_VMEST_CAUSE_SFT);
+	do_trap0(regs);
+}

arch/hexagon/kernel/vm_entry.S

@@ -367,6 +367,9 @@ _K_enter_trap0:
 _K_enter_machcheck:
 	vm_event_entry(do_machcheck)
 
+	.globl _K_enter_debug
+_K_enter_debug:
+	vm_event_entry(do_debug_exception)
 
 	.globl ret_from_fork
 ret_from_fork:

arch/hexagon/kernel/vm_vectors.S

@@ -41,7 +41,7 @@ _K_VM_event_vector:
 	jump 1b;  /*  Reset  */
 	jump _K_enter_machcheck;
 	jump _K_enter_genex;
-	jump 1b;  /*  3 Rsvd  */
+	jump _K_enter_debug;
 	jump 1b;  /*  4 Rsvd  */
 	jump _K_enter_trap0;
 	jump 1b;  /*  6 Rsvd  */