quoted

  static void set_debug_reg_defaults(struct thread_struct *thread)
  {
-    thread->hw_brk.address = 0;
-    thread->hw_brk.type = 0;
-    thread->hw_brk.len = 0;
-    thread->hw_brk.hw_len = 0;
-    if (ppc_breakpoint_available())
-        set_breakpoint(&thread->hw_brk);
+    int i;
+
+    for (i = 0; i < nr_wp_slots(); i++) {

Maybe you could add the following that you added other places:

     struct arch_hw_breakpoint null_brk = {0};

Then do

     thread->hw_brk[i] = null_brk;

Yes that's better.

[...]

quoted

+static void switch_hw_breakpoint(struct task_struct *new)
+{
+    int i;
+
+    for (i = 0; i < nr_wp_slots(); i++) {
+        if (unlikely(!hw_brk_match(this_cpu_ptr(&current_brk[i]),
+                       &new->thread.hw_brk[i]))) {
+            __set_breakpoint(&new->thread.hw_brk[i], i);
+        }

Or could be:

         if (likely(hw_brk_match(this_cpu_ptr(&current_brk[i]),
                     &new->thread.hw_brk[i])))
             continue;
         __set_breakpoint(&new->thread.hw_brk[i], i);

Sure.

[...]

quoted

@@ -128,8 +131,10 @@ static void do_signal(struct task_struct *tsk)

       * user space. The DABR will have been cleared if it
       * triggered inside the kernel.
       */
-    if (tsk->thread.hw_brk.address && tsk->thread.hw_brk.type)
-        __set_breakpoint(&tsk->thread.hw_brk, 0);
+    for (i = 0; i < nr_wp_slots(); i++) {
+        if (tsk->thread.hw_brk[i].address && tsk->thread.hw_brk[i].type)
+            __set_breakpoint(&tsk->thread.hw_brk[i], i);
+    }

thread.hwbrk also exists when CONFIG_PPC_ADV_DEBUG_REGS is selected.

You could replace the #ifndef CONFIG_PPC_ADV_DEBUG_REGS by an if (!IS_ENABLED(CONFIG_PPC_ADV_DEBUG_REGS)) and then no need of an ifdef when declaring the int i;

Makes sense. Will change it.

Ravi