ARM: 6768/1: hw_breakpoint: ensure debug logic is powered up on v7 cores

ARMv7 allows the debug core logic to be powered down and provides the
DBGPRSR register so that software can power-up and check the status of
the logic.

This patch ensures that the debug logic is powered up on ARMv7 cores
before we attempt to access the extended debug registers.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 23 insertions, 3 deletions

diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
index d600bd350704..44b84fe6e1b0 100644
--- a/arch/arm/kernel/hw_breakpoint.c
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -836,9 +836,11 @@ static int hw_breakpoint_pending(unsigned long addr, unsigned int fsr,
 /*
  * One-time initialisation.
  */
-static void reset_ctrl_regs(void *unused)
+static void reset_ctrl_regs(void *info)
 {
-        int i;
+        int i, cpu = smp_processor_id();
+        u32 dbg_power;
+        cpumask_t *cpumask = info;
 
         /*
          * v7 debug contains save and restore registers so that debug state
@@ -850,6 +852,17 @@ static void reset_ctrl_regs(void *unused)
          */
         if (debug_arch >= ARM_DEBUG_ARCH_V7_ECP14) {
                 /*
+                 * Ensure sticky power-down is clear (i.e. debug logic is
+                 * powered up).
+                 */
+                asm volatile("mrc p14, 0, %0, c1, c5, 4" : "=r" (dbg_power));
+                if ((dbg_power & 0x1) == 0) {
+                        pr_warning("CPU %d debug is powered down!\n", cpu);
+                        cpumask_or(cpumask, cpumask, cpumask_of(cpu));
+                        return;
+                }
+
+                /*
                  * Unconditionally clear the lock by writing a value
                  * other than 0xC5ACCE55 to the access register.
                  */
@@ -887,6 +900,7 @@ static struct notifier_block __cpuinitdata dbg_reset_nb = {
 static int __init arch_hw_breakpoint_init(void)
 {
         u32 dscr;
+        cpumask_t cpumask = { CPU_BITS_NONE };
 
         debug_arch = get_debug_arch();
 
@@ -911,7 +925,13 @@ static int __init arch_hw_breakpoint_init(void)
          * Reset the breakpoint resources. We assume that a halting
          * debugger will leave the world in a nice state for us.
          */
-        on_each_cpu(reset_ctrl_regs, NULL, 1);
+        on_each_cpu(reset_ctrl_regs, &cpumask, 1);
+        if (!cpumask_empty(&cpumask)) {
+                core_num_brps = 0;
+                core_num_reserved_brps = 0;
+                core_num_wrps = 0;
+                return 0;
+        }
 
         ARM_DBG_READ(c1, 0, dscr);
         if (dscr & ARM_DSCR_HDBGEN) {