ARM: hw_breakpoint: ensure OS lock is clear before writing to debug registers

[deliverable/linux.git] / arch / arm / kernel / hw_breakpoint.c

diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
index 21e3a4ab3b8c58047304b694aa8161b9ebbf1c31..793959ec8982841fd59f948633e979b4bcbfcd49 100644 (file)
--- a/arch/arm/kernel/hw_breakpoint.c
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -768,6 +768,23 @@ static void __init reset_ctrl_regs(void *unused)
 {
        int i;
 
+       /*
+        * v7 debug contains save and restore registers so that debug state
+        * can be maintained across low-power modes without leaving
+        * the debug logic powered up. It is IMPLEMENTATION DEFINED whether
+        * we can write to the debug registers out of reset, so we must
+        * unlock the OS Lock Access Register to avoid taking undefined
+        * instruction exceptions later on.
+        */
+       if (debug_arch >= ARM_DEBUG_ARCH_V7_ECP14) {
+               /*
+                * Unconditionally clear the lock by writing a value
+                * other than 0xC5ACCE55 to the access register.
+                */
+               asm volatile("mcr p14, 0, %0, c1, c0, 4" : : "r" (0));
+               isb();
+       }
+
        if (enable_monitor_mode())
                return;
 
@@ -810,17 +827,17 @@ static int __init arch_hw_breakpoint_init(void)
                pr_warning("halting debug mode enabled. Assuming maximum "
                                "watchpoint size of 4 bytes.");
        } else {
-               /* Work out the maximum supported watchpoint length. */
-               max_watchpoint_len = get_max_wp_len();
-               pr_info("maximum watchpoint size is %u bytes.\n",
-                               max_watchpoint_len);
-
                /*
                 * Reset the breakpoint resources. We assume that a halting
                 * debugger will leave the world in a nice state for us.
                 */
                smp_call_function(reset_ctrl_regs, NULL, 1);
                reset_ctrl_regs(NULL);
+
+               /* Work out the maximum supported watchpoint length. */
+               max_watchpoint_len = get_max_wp_len();
+               pr_info("maximum watchpoint size is %u bytes.\n",
+                               max_watchpoint_len);
        }
 
        /* Register debug fault handler. */