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>

diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
index d600bd3..44b84fe 100644 (file)
--- 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
@@ -849,6 +851,17 @@ static void reset_ctrl_regs(void *unused)
         * later on.
         */
        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) {