[AVR32] Enable debugging only when needed

Keep track of processes being debugged (including the kernel itself)
and turn the OCD system on and off as appropriate. Since enabling
debugging turns off some optimizations in the CPU core, this fixes the
issue that enabling KProbes support or simply running a program under
gdbserver will reduce system performance significantly until the next
reboot.

The CPU performance will still be reduced for all processes while a
process is being debugged, but this is a lot better than reducing the
performance forever.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>

5 files changed, 171 insertions, 9 deletions

diff --git a/arch/avr32/kernel/Makefile b/arch/avr32/kernel/Makefile
index 2d6d48f..bc224a4 100644
--- a/arch/avr32/kernel/Makefile
+++ b/arch/avr32/kernel/Makefile
@@ -6,7 +6,7 @@ extra-y				:= head.o vmlinux.lds
 
 obj-$(CONFIG_SUBARCH_AVR32B)	+= entry-avr32b.o
 obj-y				+= syscall_table.o syscall-stubs.o irq.o
-obj-y				+= setup.o traps.o semaphore.o ptrace.o
+obj-y				+= setup.o traps.o semaphore.o ocd.o ptrace.o
 obj-y				+= signal.o sys_avr32.o process.o time.o
 obj-y				+= init_task.o switch_to.o cpu.o
 obj-$(CONFIG_MODULES)		+= module.o avr32_ksyms.o
diff --git a/arch/avr32/kernel/kprobes.c b/arch/avr32/kernel/kprobes.c
index 799ba89..f820e9f 100644
--- a/arch/avr32/kernel/kprobes.c
+++ b/arch/avr32/kernel/kprobes.c
@@ -48,6 +48,7 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 void __kprobes arch_arm_kprobe(struct kprobe *p)
 {
 	pr_debug("arming kprobe at %p\n", p->addr);
+	ocd_enable(NULL);
 	*p->addr = BREAKPOINT_INSTRUCTION;
 	flush_icache_range((unsigned long)p->addr,
 			   (unsigned long)p->addr + sizeof(kprobe_opcode_t));
@@ -56,6 +57,7 @@ void __kprobes arch_arm_kprobe(struct kprobe *p)
 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 {
 	pr_debug("disarming kprobe at %p\n", p->addr);
+	ocd_disable(NULL);
 	*p->addr = p->opcode;
 	flush_icache_range((unsigned long)p->addr,
 			   (unsigned long)p->addr + sizeof(kprobe_opcode_t));
@@ -260,9 +262,6 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 
 int __init arch_init_kprobes(void)
 {
-	printk("KPROBES: Enabling monitor mode (MM|DBE)...\n");
-	ocd_write(DC, (1 << OCD_DC_MM_BIT) | (1 << OCD_DC_DBE_BIT));
-
 	/* TODO: Register kretprobe trampoline */
 	return 0;
 }
diff --git a/arch/avr32/kernel/ocd.c b/arch/avr32/kernel/ocd.c
new file mode 100644
index 0000000..c4f0232
--- /dev/null
+++ b/arch/avr32/kernel/ocd.c
@@ -0,0 +1,163 @@
+/*
+ * Copyright (C) 2007 Atmel Corporation
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/spinlock.h>
+
+#include <asm/ocd.h>
+
+static long ocd_count;
+static spinlock_t ocd_lock;
+
+/**
+ * ocd_enable - enable on-chip debugging
+ * @child: task to be debugged
+ *
+ * If @child is non-NULL, ocd_enable() first checks if debugging has
+ * already been enabled for @child, and if it has, does nothing.
+ *
+ * If @child is NULL (e.g. when debugging the kernel), or debugging
+ * has not already been enabled for it, ocd_enable() increments the
+ * reference count and enables the debugging hardware.
+ */
+void ocd_enable(struct task_struct *child)
+{
+	u32 dc;
+
+	if (child)
+		pr_debug("ocd_enable: child=%s [%u]\n",
+				child->comm, child->pid);
+	else
+		pr_debug("ocd_enable (no child)\n");
+
+	if (!child || !test_and_set_tsk_thread_flag(child, TIF_DEBUG)) {
+		spin_lock(&ocd_lock);
+		ocd_count++;
+		dc = ocd_read(DC);
+		dc |= (1 << OCD_DC_MM_BIT) | (1 << OCD_DC_DBE_BIT);
+		ocd_write(DC, dc);
+		spin_unlock(&ocd_lock);
+	}
+}
+
+/**
+ * ocd_disable - disable on-chip debugging
+ * @child: task that was being debugged, but isn't anymore
+ *
+ * If @child is non-NULL, ocd_disable() checks if debugging is enabled
+ * for @child, and if it isn't, does nothing.
+ *
+ * If @child is NULL (e.g. when debugging the kernel), or debugging is
+ * enabled, ocd_disable() decrements the reference count, and if it
+ * reaches zero, disables the debugging hardware.
+ */
+void ocd_disable(struct task_struct *child)
+{
+	u32 dc;
+
+	if (!child)
+		pr_debug("ocd_disable (no child)\n");
+	else if (test_tsk_thread_flag(child, TIF_DEBUG))
+		pr_debug("ocd_disable: child=%s [%u]\n",
+				child->comm, child->pid);
+
+	if (!child || test_and_clear_tsk_thread_flag(child, TIF_DEBUG)) {
+		spin_lock(&ocd_lock);
+		ocd_count--;
+
+		WARN_ON(ocd_count < 0);
+
+		if (ocd_count <= 0) {
+			dc = ocd_read(DC);
+			dc &= ~((1 << OCD_DC_MM_BIT) | (1 << OCD_DC_DBE_BIT));
+			ocd_write(DC, dc);
+		}
+		spin_unlock(&ocd_lock);
+	}
+}
+
+#ifdef CONFIG_DEBUG_FS
+#include <linux/debugfs.h>
+#include <linux/module.h>
+
+static struct dentry *ocd_debugfs_root;
+static struct dentry *ocd_debugfs_DC;
+static struct dentry *ocd_debugfs_DS;
+static struct dentry *ocd_debugfs_count;
+
+static u64 ocd_DC_get(void *data)
+{
+	return ocd_read(DC);
+}
+static void ocd_DC_set(void *data, u64 val)
+{
+	ocd_write(DC, val);
+}
+DEFINE_SIMPLE_ATTRIBUTE(fops_DC, ocd_DC_get, ocd_DC_set, "0x%08llx\n");
+
+static u64 ocd_DS_get(void *data)
+{
+	return ocd_read(DS);
+}
+DEFINE_SIMPLE_ATTRIBUTE(fops_DS, ocd_DS_get, NULL, "0x%08llx\n");
+
+static u64 ocd_count_get(void *data)
+{
+	return ocd_count;
+}
+DEFINE_SIMPLE_ATTRIBUTE(fops_count, ocd_count_get, NULL, "%lld\n");
+
+static void ocd_debugfs_init(void)
+{
+	struct dentry *root;
+
+	root = debugfs_create_dir("ocd", NULL);
+	if (IS_ERR(root) || !root)
+		goto err_root;
+	ocd_debugfs_root = root;
+
+	ocd_debugfs_DC = debugfs_create_file("DC", S_IRUSR | S_IWUSR,
+				root, NULL, &fops_DC);
+	if (!ocd_debugfs_DC)
+		goto err_DC;
+
+	ocd_debugfs_DS = debugfs_create_file("DS", S_IRUSR, root,
+				NULL, &fops_DS);
+	if (!ocd_debugfs_DS)
+		goto err_DS;
+
+	ocd_debugfs_count = debugfs_create_file("count", S_IRUSR, root,
+				NULL, &fops_count);
+	if (!ocd_debugfs_count)
+		goto err_count;
+
+	return;
+
+err_count:
+	debugfs_remove(ocd_debugfs_DS);
+err_DS:
+	debugfs_remove(ocd_debugfs_DC);
+err_DC:
+	debugfs_remove(ocd_debugfs_root);
+err_root:
+	printk(KERN_WARNING "OCD: Failed to create debugfs entries\n");
+}
+#else
+static inline void ocd_debugfs_init(void)
+{
+
+}
+#endif
+
+static int __init ocd_init(void)
+{
+	spin_lock_init(&ocd_lock);
+	ocd_debugfs_init();
+	return 0;
+}
+arch_initcall(ocd_init);
diff --git a/arch/avr32/kernel/process.c b/arch/avr32/kernel/process.c
index 9d6dac8..eaaa69b 100644
--- a/arch/avr32/kernel/process.c
+++ b/arch/avr32/kernel/process.c
@@ -103,7 +103,7 @@ EXPORT_SYMBOL(kernel_thread);
  */
 void exit_thread(void)
 {
-	/* nothing to do */
+	ocd_disable(current);
 }
 
 void flush_thread(void)
@@ -345,6 +345,9 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long usp,
 	p->thread.cpu_context.ksp = (unsigned long)childregs;
 	p->thread.cpu_context.pc = (unsigned long)ret_from_fork;
 
+	if ((clone_flags & CLONE_PTRACE) && test_thread_flag(TIF_DEBUG))
+		ocd_enable(p);
+
 	return 0;
 }
 
diff --git a/arch/avr32/kernel/ptrace.c b/arch/avr32/kernel/ptrace.c
index 002369e..1fed38f 100644
--- a/arch/avr32/kernel/ptrace.c
+++ b/arch/avr32/kernel/ptrace.c
@@ -58,6 +58,7 @@ void ptrace_disable(struct task_struct *child)
 {
 	clear_tsk_thread_flag(child, TIF_SINGLE_STEP);
 	clear_tsk_thread_flag(child, TIF_BREAKPOINT);
+	ocd_disable(child);
 }
 
 /*
@@ -144,10 +145,6 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 {
 	int ret;
 
-	pr_debug("ptrace: Enabling monitor mode...\n");
-	ocd_write(DC, ocd_read(DC) | (1 << OCD_DC_MM_BIT)
-			| (1 << OCD_DC_DBE_BIT));
-
 	switch (request) {
 	/* Read the word at location addr in the child process */
 	case PTRACE_PEEKTEXT: