ARM: hw_breakpoint: do not fail initcall if monitor mode is disabled
The debug registers can only be manipulated from software if monitor
debug mode is enabled. On some cores, this can never be enabled (i.e.
the corresponding bit in the DSCR is RAZ/WI).
This patch ensures we can handle this hardware configuration and fail
gracefully, rather than blow up the kernel during boot.
Reported-by: Cyril Chemparathy <cyril@ti.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
index 56ed9a6..c9f3f04 100644
--- a/arch/arm/kernel/hw_breakpoint.c
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -219,23 +219,6 @@
return brps;
}
-int hw_breakpoint_slots(int type)
-{
- /*
- * We can be called early, so don't rely on
- * our static variables being initialised.
- */
- switch (type) {
- case TYPE_INST:
- return get_num_brps();
- case TYPE_DATA:
- return get_num_wrps();
- default:
- pr_warning("unknown slot type: %d\n", type);
- return 0;
- }
-}
-
/*
* In order to access the breakpoint/watchpoint control registers,
* we must be running in debug monitor mode. Unfortunately, we can
@@ -256,8 +239,12 @@
goto out;
}
+ /* If monitor mode is already enabled, just return. */
+ if (dscr & ARM_DSCR_MDBGEN)
+ goto out;
+
/* Write to the corresponding DSCR. */
- switch (debug_arch) {
+ switch (get_debug_arch()) {
case ARM_DEBUG_ARCH_V6:
case ARM_DEBUG_ARCH_V6_1:
ARM_DBG_WRITE(c1, 0, (dscr | ARM_DSCR_MDBGEN));
@@ -272,15 +259,30 @@
/* Check that the write made it through. */
ARM_DBG_READ(c1, 0, dscr);
- if (WARN_ONCE(!(dscr & ARM_DSCR_MDBGEN),
- "failed to enable monitor mode.")) {
+ if (!(dscr & ARM_DSCR_MDBGEN))
ret = -EPERM;
- }
out:
return ret;
}
+int hw_breakpoint_slots(int type)
+{
+ /*
+ * We can be called early, so don't rely on
+ * our static variables being initialised.
+ */
+ switch (type) {
+ case TYPE_INST:
+ return get_num_brps();
+ case TYPE_DATA:
+ return get_num_wrps();
+ default:
+ pr_warning("unknown slot type: %d\n", type);
+ return 0;
+ }
+}
+
/*
* Check if 8-bit byte-address select is available.
* This clobbers WRP 0.
@@ -294,9 +296,6 @@
if (debug_arch < ARM_DEBUG_ARCH_V7_ECP14)
goto out;
- if (enable_monitor_mode())
- goto out;
-
memset(&ctrl, 0, sizeof(ctrl));
ctrl.len = ARM_BREAKPOINT_LEN_8;
ctrl_reg = encode_ctrl_reg(ctrl);
@@ -879,15 +878,13 @@
static int __init arch_hw_breakpoint_init(void)
{
- int ret = 0;
u32 dscr;
debug_arch = get_debug_arch();
if (debug_arch > ARM_DEBUG_ARCH_V7_ECP14) {
pr_info("debug architecture 0x%x unsupported.\n", debug_arch);
- ret = -ENODEV;
- goto out;
+ return 0;
}
/* Determine how many BRPs/WRPs are available. */
@@ -928,8 +925,7 @@
/* Register hotplug notifier. */
register_cpu_notifier(&dbg_reset_nb);
-out:
- return ret;
+ return 0;
}
arch_initcall(arch_hw_breakpoint_init);