ARM: 5841/1: a driver for on-chip ETM and ETB

This driver implements support for on-chip Embedded Tracing Macrocell and
Embedded Trace Buffer. It allows to trigger tracing of kernel execution flow
and exporting trace output to userspace via character device and a sysrq
combo.

Trace output can then be decoded by a fairly simple open source tool [1]
which is already sufficient to get the idea of what the kernel is doing.

[1]: http://github.com/virtuoso/etm2human

Signed-off-by: Alexander Shishkin <virtuoso@slind.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

4 files changed, 816 insertions, 0 deletions

diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index 1a6f70e52921..ff54c23d085e 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -83,6 +83,14 @@ config DEBUG_ICEDCC
           It does include a timeout to ensure that the system does not
           totally freeze when there is nothing connected to read.
 
+config OC_ETM
+        bool "On-chip ETM and ETB"
+        select ARM_AMBA
+        help
+          Enables the on-chip embedded trace macrocell and embedded trace
+          buffer driver that will allow you to collect traces of the
+          kernel code.
+
 config DEBUG_DC21285_PORT
         bool "Kernel low-level debugging messages via footbridge serial port"
         depends on DEBUG_LL && FOOTBRIDGE
diff --git a/arch/arm/include/asm/hardware/coresight.h b/arch/arm/include/asm/hardware/coresight.h
new file mode 100644
index 000000000000..f82b25d4f73e
--- /dev/null
+++ b/arch/arm/include/asm/hardware/coresight.h
@@ -0,0 +1,165 @@
+/*
+ * linux/arch/arm/include/asm/hardware/coresight.h
+ *
+ * CoreSight components' registers
+ *
+ * Copyright (C) 2009 Nokia Corporation.
+ * Alexander Shishkin
+ *
+ * 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.
+ */
+
+#ifndef __ASM_HARDWARE_CORESIGHT_H
+#define __ASM_HARDWARE_CORESIGHT_H
+
+#define TRACER_ACCESSED_BIT     0
+#define TRACER_RUNNING_BIT      1
+#define TRACER_CYCLE_ACC_BIT    2
+#define TRACER_ACCESSED         BIT(TRACER_ACCESSED_BIT)
+#define TRACER_RUNNING          BIT(TRACER_RUNNING_BIT)
+#define TRACER_CYCLE_ACC        BIT(TRACER_CYCLE_ACC_BIT)
+
+struct tracectx {
+        unsigned int    etb_bufsz;
+        void __iomem    *etb_regs;
+        void __iomem    *etm_regs;
+        unsigned long   flags;
+        int             ncmppairs;
+        int             etm_portsz;
+        struct device   *dev;
+        struct clk      *emu_clk;
+        struct mutex    mutex;
+};
+
+#define TRACER_TIMEOUT 10000
+
+#define etm_writel(t, v, x) \
+        (__raw_writel((v), (t)->etm_regs + (x)))
+#define etm_readl(t, x) (__raw_readl((t)->etm_regs + (x)))
+
+/* CoreSight Management Registers */
+#define CSMR_LOCKACCESS 0xfb0
+#define CSMR_LOCKSTATUS 0xfb4
+#define CSMR_AUTHSTATUS 0xfb8
+#define CSMR_DEVID      0xfc8
+#define CSMR_DEVTYPE    0xfcc
+/* CoreSight Component Registers */
+#define CSCR_CLASS      0xff4
+
+#define CSCR_PRSR       0x314
+
+#define UNLOCK_MAGIC    0xc5acce55
+
+/* ETM control register, "ETM Architecture", 3.3.1 */
+#define ETMR_CTRL               0
+#define ETMCTRL_POWERDOWN       1
+#define ETMCTRL_PROGRAM         (1 << 10)
+#define ETMCTRL_PORTSEL         (1 << 11)
+#define ETMCTRL_DO_CONTEXTID    (3 << 14)
+#define ETMCTRL_PORTMASK1       (7 << 4)
+#define ETMCTRL_PORTMASK2       (1 << 21)
+#define ETMCTRL_PORTMASK        (ETMCTRL_PORTMASK1 | ETMCTRL_PORTMASK2)
+#define ETMCTRL_PORTSIZE(x) ((((x) & 7) << 4) | (!!((x) & 8)) << 21)
+#define ETMCTRL_DO_CPRT         (1 << 1)
+#define ETMCTRL_DATAMASK        (3 << 2)
+#define ETMCTRL_DATA_DO_DATA    (1 << 2)
+#define ETMCTRL_DATA_DO_ADDR    (1 << 3)
+#define ETMCTRL_DATA_DO_BOTH    (ETMCTRL_DATA_DO_DATA | ETMCTRL_DATA_DO_ADDR)
+#define ETMCTRL_BRANCH_OUTPUT   (1 << 8)
+#define ETMCTRL_CYCLEACCURATE   (1 << 12)
+
+/* ETM configuration code register */
+#define ETMR_CONFCODE           (0x04)
+
+/* ETM trace start/stop resource control register */
+#define ETMR_TRACESSCTRL        (0x18)
+
+/* ETM trigger event register */
+#define ETMR_TRIGEVT            (0x08)
+
+/* address access type register bits, "ETM architecture",
+ * table 3-27 */
+/* - access type */
+#define ETMAAT_IFETCH           0
+#define ETMAAT_IEXEC            1
+#define ETMAAT_IEXECPASS        2
+#define ETMAAT_IEXECFAIL        3
+#define ETMAAT_DLOADSTORE       4
+#define ETMAAT_DLOAD            5
+#define ETMAAT_DSTORE           6
+/* - comparison access size */
+#define ETMAAT_JAVA             (0 << 3)
+#define ETMAAT_THUMB            (1 << 3)
+#define ETMAAT_ARM              (3 << 3)
+/* - data value comparison control */
+#define ETMAAT_NOVALCMP         (0 << 5)
+#define ETMAAT_VALMATCH         (1 << 5)
+#define ETMAAT_VALNOMATCH       (3 << 5)
+/* - exact match */
+#define ETMAAT_EXACTMATCH       (1 << 7)
+/* - context id comparator control */
+#define ETMAAT_IGNCONTEXTID     (0 << 8)
+#define ETMAAT_VALUE1           (1 << 8)
+#define ETMAAT_VALUE2           (2 << 8)
+#define ETMAAT_VALUE3           (3 << 8)
+/* - security level control */
+#define ETMAAT_IGNSECURITY      (0 << 10)
+#define ETMAAT_NSONLY           (1 << 10)
+#define ETMAAT_SONLY            (2 << 10)
+
+#define ETMR_COMP_VAL(x)        (0x40 + (x) * 4)
+#define ETMR_COMP_ACC_TYPE(x)   (0x80 + (x) * 4)
+
+/* ETM status register, "ETM Architecture", 3.3.2 */
+#define ETMR_STATUS             (0x10)
+#define ETMST_OVERFLOW          (1 << 0)
+#define ETMST_PROGBIT           (1 << 1)
+#define ETMST_STARTSTOP         (1 << 2)
+#define ETMST_TRIGGER           (1 << 3)
+
+#define etm_progbit(t)          (etm_readl((t), ETMR_STATUS) & ETMST_PROGBIT)
+#define etm_started(t)          (etm_readl((t), ETMR_STATUS) & ETMST_STARTSTOP)
+#define etm_triggered(t)        (etm_readl((t), ETMR_STATUS) & ETMST_TRIGGER)
+
+#define ETMR_TRACEENCTRL2       0x1c
+#define ETMR_TRACEENCTRL        0x24
+#define ETMTE_INCLEXCL          (1 << 24)
+#define ETMR_TRACEENEVT         0x20
+#define ETMCTRL_OPTS            (ETMCTRL_DO_CPRT | \
+                                ETMCTRL_DATA_DO_ADDR | \
+                                ETMCTRL_BRANCH_OUTPUT | \
+                                ETMCTRL_DO_CONTEXTID)
+
+/* ETB registers, "CoreSight Components TRM", 9.3 */
+#define ETBR_DEPTH              0x04
+#define ETBR_STATUS             0x0c
+#define ETBR_READMEM            0x10
+#define ETBR_READADDR           0x14
+#define ETBR_WRITEADDR          0x18
+#define ETBR_TRIGGERCOUNT       0x1c
+#define ETBR_CTRL               0x20
+#define ETBR_FORMATTERCTRL      0x304
+#define ETBFF_ENFTC             1
+#define ETBFF_ENFCONT           (1 << 1)
+#define ETBFF_FONFLIN           (1 << 4)
+#define ETBFF_MANUAL_FLUSH      (1 << 6)
+#define ETBFF_TRIGIN            (1 << 8)
+#define ETBFF_TRIGEVT           (1 << 9)
+#define ETBFF_TRIGFL            (1 << 10)
+
+#define etb_writel(t, v, x) \
+        (__raw_writel((v), (t)->etb_regs + (x)))
+#define etb_readl(t, x) (__raw_readl((t)->etb_regs + (x)))
+
+#define etm_lock(t) do { etm_writel((t), 0, CSMR_LOCKACCESS); } while (0)
+#define etm_unlock(t) \
+        do { etm_writel((t), UNLOCK_MAGIC, CSMR_LOCKACCESS); } while (0)
+
+#define etb_lock(t) do { etb_writel((t), 0, CSMR_LOCKACCESS); } while (0)
+#define etb_unlock(t) \
+        do { etb_writel((t), UNLOCK_MAGIC, CSMR_LOCKACCESS); } while (0)
+
+#endif /* __ASM_HARDWARE_CORESIGHT_H */
+
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 79087dd6d869..e7ccf7e697ce 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -17,6 +17,8 @@ obj-y		:= compat.o elf.o entry-armv.o entry-common.o irq.o \
                    process.o ptrace.o return_address.o setup.o signal.o \
                    sys_arm.o stacktrace.o time.o traps.o
 
+obj-$(CONFIG_OC_ETM)            += etm.o
+
 obj-$(CONFIG_ISA_DMA_API)       += dma.o
 obj-$(CONFIG_ARCH_ACORN)        += ecard.o 
 obj-$(CONFIG_FIQ)               += fiq.o
diff --git a/arch/arm/kernel/etm.c b/arch/arm/kernel/etm.c
new file mode 100644
index 000000000000..827753966301
--- /dev/null
+++ b/arch/arm/kernel/etm.c
@@ -0,0 +1,641 @@
+/*
+ * linux/arch/arm/kernel/etm.c
+ *
+ * Driver for ARM's Embedded Trace Macrocell and Embedded Trace Buffer.
+ *
+ * Copyright (C) 2009 Nokia Corporation.
+ * Alexander Shishkin
+ *
+ * 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/kernel.h>
+#include <linux/init.h>
+#include <linux/types.h>
+#include <linux/io.h>
+#include <linux/sysrq.h>
+#include <linux/device.h>
+#include <linux/clk.h>
+#include <linux/amba/bus.h>
+#include <linux/fs.h>
+#include <linux/uaccess.h>
+#include <linux/miscdevice.h>
+#include <linux/vmalloc.h>
+#include <linux/mutex.h>
+#include <asm/hardware/coresight.h>
+#include <asm/sections.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Alexander Shishkin");
+
+static struct tracectx tracer;
+
+static inline bool trace_isrunning(struct tracectx *t)
+{
+        return !!(t->flags & TRACER_RUNNING);
+}
+
+static int etm_setup_address_range(struct tracectx *t, int n,
+                unsigned long start, unsigned long end, int exclude, int data)
+{
+        u32 flags = ETMAAT_ARM | ETMAAT_IGNCONTEXTID | ETMAAT_NSONLY | \
+                    ETMAAT_NOVALCMP;
+
+        if (n < 1 || n > t->ncmppairs)
+                return -EINVAL;
+
+        /* comparators and ranges are numbered starting with 1 as opposed
+         * to bits in a word */
+        n--;
+
+        if (data)
+                flags |= ETMAAT_DLOADSTORE;
+        else
+                flags |= ETMAAT_IEXEC;
+
+        /* first comparator for the range */
+        etm_writel(t, flags, ETMR_COMP_ACC_TYPE(n * 2));
+        etm_writel(t, start, ETMR_COMP_VAL(n * 2));
+
+        /* second comparator is right next to it */
+        etm_writel(t, flags, ETMR_COMP_ACC_TYPE(n * 2 + 1));
+        etm_writel(t, end, ETMR_COMP_VAL(n * 2 + 1));
+
+        flags = exclude ? ETMTE_INCLEXCL : 0;
+        etm_writel(t, flags | (1 << n), ETMR_TRACEENCTRL);
+
+        return 0;
+}
+
+static int trace_start(struct tracectx *t)
+{
+        u32 v;
+        unsigned long timeout = TRACER_TIMEOUT;
+
+        etb_unlock(t);
+
+        etb_writel(t, 0, ETBR_FORMATTERCTRL);
+        etb_writel(t, 1, ETBR_CTRL);
+
+        etb_lock(t);
+
+        /* configure etm */
+        v = ETMCTRL_OPTS | ETMCTRL_PROGRAM | ETMCTRL_PORTSIZE(t->etm_portsz);
+
+        if (t->flags & TRACER_CYCLE_ACC)
+                v |= ETMCTRL_CYCLEACCURATE;
+
+        etm_unlock(t);
+
+        etm_writel(t, v, ETMR_CTRL);
+
+        while (!(etm_readl(t, ETMR_CTRL) & ETMCTRL_PROGRAM) && --timeout)
+                ;
+        if (!timeout) {
+                dev_dbg(t->dev, "Waiting for progbit to assert timed out\n");
+                etm_lock(t);
+                return -EFAULT;
+        }
+
+        etm_setup_address_range(t, 1, (unsigned long)_stext,
+                        (unsigned long)_etext, 0, 0);
+        etm_writel(t, 0, ETMR_TRACEENCTRL2);
+        etm_writel(t, 0, ETMR_TRACESSCTRL);
+        etm_writel(t, 0x6f, ETMR_TRACEENEVT);
+
+        v &= ~ETMCTRL_PROGRAM;
+        v |= ETMCTRL_PORTSEL;
+
+        etm_writel(t, v, ETMR_CTRL);
+
+        timeout = TRACER_TIMEOUT;
+        while (etm_readl(t, ETMR_CTRL) & ETMCTRL_PROGRAM && --timeout)
+                ;
+        if (!timeout) {
+                dev_dbg(t->dev, "Waiting for progbit to deassert timed out\n");
+                etm_lock(t);
+                return -EFAULT;
+        }
+
+        etm_lock(t);
+
+        t->flags |= TRACER_RUNNING;
+
+        return 0;
+}
+
+static int trace_stop(struct tracectx *t)
+{
+        unsigned long timeout = TRACER_TIMEOUT;
+
+        etm_unlock(t);
+
+        etm_writel(t, 0x440, ETMR_CTRL);
+        while (!(etm_readl(t, ETMR_CTRL) & ETMCTRL_PROGRAM) && --timeout)
+                ;
+        if (!timeout) {
+                dev_dbg(t->dev, "Waiting for progbit to assert timed out\n");
+                etm_lock(t);
+                return -EFAULT;
+        }
+
+        etm_lock(t);
+
+        etb_unlock(t);
+        etb_writel(t, ETBFF_MANUAL_FLUSH, ETBR_FORMATTERCTRL);
+
+        timeout = TRACER_TIMEOUT;
+        while (etb_readl(t, ETBR_FORMATTERCTRL) &
+                        ETBFF_MANUAL_FLUSH && --timeout)
+                ;
+        if (!timeout) {
+                dev_dbg(t->dev, "Waiting for formatter flush to commence "
+                                "timed out\n");
+                etb_lock(t);
+                return -EFAULT;
+        }
+
+        etb_writel(t, 0, ETBR_CTRL);
+
+        etb_lock(t);
+
+        t->flags &= ~TRACER_RUNNING;
+
+        return 0;
+}
+
+static int etb_getdatalen(struct tracectx *t)
+{
+        u32 v;
+        int rp, wp;
+
+        v = etb_readl(t, ETBR_STATUS);
+
+        if (v & 1)
+                return t->etb_bufsz;
+
+        rp = etb_readl(t, ETBR_READADDR);
+        wp = etb_readl(t, ETBR_WRITEADDR);
+
+        if (rp > wp) {
+                etb_writel(t, 0, ETBR_READADDR);
+                etb_writel(t, 0, ETBR_WRITEADDR);
+
+                return 0;
+        }
+
+        return wp - rp;
+}
+
+/* sysrq+v will always stop the running trace and leave it at that */
+static void etm_dump(void)
+{
+        struct tracectx *t = &tracer;
+        u32 first = 0;
+        int length;
+
+        if (!t->etb_regs) {
+                printk(KERN_INFO "No tracing hardware found\n");
+                return;
+        }
+
+        if (trace_isrunning(t))
+                trace_stop(t);
+
+        etb_unlock(t);
+
+        length = etb_getdatalen(t);
+
+        if (length == t->etb_bufsz)
+                first = etb_readl(t, ETBR_WRITEADDR);
+
+        etb_writel(t, first, ETBR_READADDR);
+
+        printk(KERN_INFO "Trace buffer contents length: %d\n", length);
+        printk(KERN_INFO "--- ETB buffer begin ---\n");
+        for (; length; length--)
+                printk("%08x", cpu_to_be32(etb_readl(t, ETBR_READMEM)));
+        printk(KERN_INFO "\n--- ETB buffer end ---\n");
+
+        /* deassert the overflow bit */
+        etb_writel(t, 1, ETBR_CTRL);
+        etb_writel(t, 0, ETBR_CTRL);
+
+        etb_writel(t, 0, ETBR_TRIGGERCOUNT);
+        etb_writel(t, 0, ETBR_READADDR);
+        etb_writel(t, 0, ETBR_WRITEADDR);
+
+        etb_lock(t);
+}
+
+static void sysrq_etm_dump(int key, struct tty_struct *tty)
+{
+        dev_dbg(tracer.dev, "Dumping ETB buffer\n");
+        etm_dump();
+}
+
+static struct sysrq_key_op sysrq_etm_op = {
+        .handler = sysrq_etm_dump,
+        .help_msg = "ETM buffer dump",
+        .action_msg = "etm",
+};
+
+static int etb_open(struct inode *inode, struct file *file)
+{
+        if (!tracer.etb_regs)
+                return -ENODEV;
+
+        file->private_data = &tracer;
+
+        return nonseekable_open(inode, file);
+}
+
+static ssize_t etb_read(struct file *file, char __user *data,
+                size_t len, loff_t *ppos)
+{
+        int total, i;
+        long length;
+        struct tracectx *t = file->private_data;
+        u32 first = 0;
+        u32 *buf;
+
+        mutex_lock(&t->mutex);
+
+        if (trace_isrunning(t)) {
+                length = 0;
+                goto out;
+        }
+
+        etb_unlock(t);
+
+        total = etb_getdatalen(t);
+        if (total == t->etb_bufsz)
+                first = etb_readl(t, ETBR_WRITEADDR);
+
+        etb_writel(t, first, ETBR_READADDR);
+
+        length = min(total * 4, (int)len);
+        buf = vmalloc(length);
+
+        dev_dbg(t->dev, "ETB buffer length: %d\n", total);
+        dev_dbg(t->dev, "ETB status reg: %x\n", etb_readl(t, ETBR_STATUS));
+        for (i = 0; i < length / 4; i++)
+                buf[i] = etb_readl(t, ETBR_READMEM);
+
+        /* the only way to deassert overflow bit in ETB status is this */
+        etb_writel(t, 1, ETBR_CTRL);
+        etb_writel(t, 0, ETBR_CTRL);
+
+        etb_writel(t, 0, ETBR_WRITEADDR);
+        etb_writel(t, 0, ETBR_READADDR);
+        etb_writel(t, 0, ETBR_TRIGGERCOUNT);
+
+        etb_lock(t);
+
+        length -= copy_to_user(data, buf, length);
+        vfree(buf);
+
+out:
+        mutex_unlock(&t->mutex);
+
+        return length;
+}
+
+static int etb_release(struct inode *inode, struct file *file)
+{
+        /* there's nothing to do here, actually */
+        return 0;
+}
+
+static const struct file_operations etb_fops = {
+        .owner = THIS_MODULE,
+        .read = etb_read,
+        .open = etb_open,
+        .release = etb_release,
+};
+
+static struct miscdevice etb_miscdev = {
+        .name = "tracebuf",
+        .minor = 0,
+        .fops = &etb_fops,
+};
+
+static int __init etb_probe(struct amba_device *dev, struct amba_id *id)
+{
+        struct tracectx *t = &tracer;
+        int ret = 0;
+
+        ret = amba_request_regions(dev, NULL);
+        if (ret)
+                goto out;
+
+        t->etb_regs = ioremap_nocache(dev->res.start, resource_size(&dev->res));
+        if (!t->etb_regs) {
+                ret = -ENOMEM;
+                goto out_release;
+        }
+
+        amba_set_drvdata(dev, t);
+
+        etb_miscdev.parent = &dev->dev;
+
+        ret = misc_register(&etb_miscdev);
+        if (ret)
+                goto out_unmap;
+
+        t->emu_clk = clk_get(&dev->dev, "emu_src_ck");
+        if (IS_ERR(t->emu_clk)) {
+                dev_dbg(&dev->dev, "Failed to obtain emu_src_ck.\n");
+                return -EFAULT;
+        }
+
+        clk_enable(t->emu_clk);
+
+        etb_unlock(t);
+        t->etb_bufsz = etb_readl(t, ETBR_DEPTH);
+        dev_dbg(&dev->dev, "Size: %x\n", t->etb_bufsz);
+
+        /* make sure trace capture is disabled */
+        etb_writel(t, 0, ETBR_CTRL);
+        etb_writel(t, 0x1000, ETBR_FORMATTERCTRL);
+        etb_lock(t);
+
+        dev_dbg(&dev->dev, "ETB AMBA driver initialized.\n");
+
+out:
+        return ret;
+
+out_unmap:
+        amba_set_drvdata(dev, NULL);
+        iounmap(t->etb_regs);
+
+out_release:
+        amba_release_regions(dev);
+
+        return ret;
+}
+
+static int etb_remove(struct amba_device *dev)
+{
+        struct tracectx *t = amba_get_drvdata(dev);
+
+        amba_set_drvdata(dev, NULL);
+
+        iounmap(t->etb_regs);
+        t->etb_regs = NULL;
+
+        clk_disable(t->emu_clk);
+        clk_put(t->emu_clk);
+
+        amba_release_regions(dev);
+
+        return 0;
+}
+
+static struct amba_id etb_ids[] = {
+        {
+                .id     = 0x0003b907,
+                .mask   = 0x0007ffff,
+        },
+        { 0, 0 },
+};
+
+static struct amba_driver etb_driver = {
+        .drv            = {
+                .name   = "etb",
+                .owner  = THIS_MODULE,
+        },
+        .probe          = etb_probe,
+        .remove         = etb_remove,
+        .id_table       = etb_ids,
+};
+
+/* use a sysfs file "trace_running" to start/stop tracing */
+static ssize_t trace_running_show(struct kobject *kobj,
+                                  struct kobj_attribute *attr,
+                                  char *buf)
+{
+        return sprintf(buf, "%x\n", trace_isrunning(&tracer));
+}
+
+static ssize_t trace_running_store(struct kobject *kobj,
+                                   struct kobj_attribute *attr,
+                                   const char *buf, size_t n)
+{
+        unsigned int value;
+        int ret;
+
+        if (sscanf(buf, "%u", &value) != 1)
+                return -EINVAL;
+
+        mutex_lock(&tracer.mutex);
+        ret = value ? trace_start(&tracer) : trace_stop(&tracer);
+        mutex_unlock(&tracer.mutex);
+
+        return ret ? : n;
+}
+
+static struct kobj_attribute trace_running_attr =
+        __ATTR(trace_running, 0644, trace_running_show, trace_running_store);
+
+static ssize_t trace_info_show(struct kobject *kobj,
+                                  struct kobj_attribute *attr,
+                                  char *buf)
+{
+        u32 etb_wa, etb_ra, etb_st, etb_fc, etm_ctrl, etm_st;
+        int datalen;
+
+        etb_unlock(&tracer);
+        datalen = etb_getdatalen(&tracer);
+        etb_wa = etb_readl(&tracer, ETBR_WRITEADDR);
+        etb_ra = etb_readl(&tracer, ETBR_READADDR);
+        etb_st = etb_readl(&tracer, ETBR_STATUS);
+        etb_fc = etb_readl(&tracer, ETBR_FORMATTERCTRL);
+        etb_lock(&tracer);
+
+        etm_unlock(&tracer);
+        etm_ctrl = etm_readl(&tracer, ETMR_CTRL);
+        etm_st = etm_readl(&tracer, ETMR_STATUS);
+        etm_lock(&tracer);
+
+        return sprintf(buf, "Trace buffer len: %d\nComparator pairs: %d\n"
+                        "ETBR_WRITEADDR:\t%08x\n"
+                        "ETBR_READADDR:\t%08x\n"
+                        "ETBR_STATUS:\t%08x\n"
+                        "ETBR_FORMATTERCTRL:\t%08x\n"
+                        "ETMR_CTRL:\t%08x\n"
+                        "ETMR_STATUS:\t%08x\n",
+                        datalen,
+                        tracer.ncmppairs,
+                        etb_wa,
+                        etb_ra,
+                        etb_st,
+                        etb_fc,
+                        etm_ctrl,
+                        etm_st
+                        );
+}
+
+static struct kobj_attribute trace_info_attr =
+        __ATTR(trace_info, 0444, trace_info_show, NULL);
+
+static ssize_t trace_mode_show(struct kobject *kobj,
+                                  struct kobj_attribute *attr,
+                                  char *buf)
+{
+        return sprintf(buf, "%d %d\n",
+                        !!(tracer.flags & TRACER_CYCLE_ACC),
+                        tracer.etm_portsz);
+}
+
+static ssize_t trace_mode_store(struct kobject *kobj,
+                                   struct kobj_attribute *attr,
+                                   const char *buf, size_t n)
+{
+        unsigned int cycacc, portsz;
+
+        if (sscanf(buf, "%u %u", &cycacc, &portsz) != 2)
+                return -EINVAL;
+
+        mutex_lock(&tracer.mutex);
+        if (cycacc)
+                tracer.flags |= TRACER_CYCLE_ACC;
+        else
+                tracer.flags &= ~TRACER_CYCLE_ACC;
+
+        tracer.etm_portsz = portsz & 0x0f;
+        mutex_unlock(&tracer.mutex);
+
+        return n;
+}
+
+static struct kobj_attribute trace_mode_attr =
+        __ATTR(trace_mode, 0644, trace_mode_show, trace_mode_store);
+
+static int __init etm_probe(struct amba_device *dev, struct amba_id *id)
+{
+        struct tracectx *t = &tracer;
+        int ret = 0;
+
+        if (t->etm_regs) {
+                dev_dbg(&dev->dev, "ETM already initialized\n");
+                ret = -EBUSY;
+                goto out;
+        }
+
+        ret = amba_request_regions(dev, NULL);
+        if (ret)
+                goto out;
+
+        t->etm_regs = ioremap_nocache(dev->res.start, resource_size(&dev->res));
+        if (!t->etm_regs) {
+                ret = -ENOMEM;
+                goto out_release;
+        }
+
+        amba_set_drvdata(dev, t);
+
+        mutex_init(&t->mutex);
+        t->dev = &dev->dev;
+        t->flags = TRACER_CYCLE_ACC;
+        t->etm_portsz = 1;
+
+        etm_unlock(t);
+        ret = etm_readl(t, CSCR_PRSR);
+
+        t->ncmppairs = etm_readl(t, ETMR_CONFCODE) & 0xf;
+        etm_writel(t, 0x440, ETMR_CTRL);
+        etm_lock(t);
+
+        ret = sysfs_create_file(&dev->dev.kobj,
+                        &trace_running_attr.attr);
+        if (ret)
+                goto out_unmap;
+
+        /* failing to create any of these two is not fatal */
+        ret = sysfs_create_file(&dev->dev.kobj, &trace_info_attr.attr);
+        if (ret)
+                dev_dbg(&dev->dev, "Failed to create trace_info in sysfs\n");
+
+        ret = sysfs_create_file(&dev->dev.kobj, &trace_mode_attr.attr);
+        if (ret)
+                dev_dbg(&dev->dev, "Failed to create trace_mode in sysfs\n");
+
+        dev_dbg(t->dev, "ETM AMBA driver initialized.\n");
+
+out:
+        return ret;
+
+out_unmap:
+        amba_set_drvdata(dev, NULL);
+        iounmap(t->etm_regs);
+
+out_release:
+        amba_release_regions(dev);
+
+        return ret;
+}
+
+static int etm_remove(struct amba_device *dev)
+{
+        struct tracectx *t = amba_get_drvdata(dev);
+
+        amba_set_drvdata(dev, NULL);
+
+        iounmap(t->etm_regs);
+        t->etm_regs = NULL;
+
+        amba_release_regions(dev);
+
+        sysfs_remove_file(&dev->dev.kobj, &trace_running_attr.attr);
+        sysfs_remove_file(&dev->dev.kobj, &trace_info_attr.attr);
+        sysfs_remove_file(&dev->dev.kobj, &trace_mode_attr.attr);
+
+        return 0;
+}
+
+static struct amba_id etm_ids[] = {
+        {
+                .id     = 0x0003b921,
+                .mask   = 0x0007ffff,
+        },
+        { 0, 0 },
+};
+
+static struct amba_driver etm_driver = {
+        .drv            = {
+                .name   = "etm",
+                .owner  = THIS_MODULE,
+        },
+        .probe          = etm_probe,
+        .remove         = etm_remove,
+        .id_table       = etm_ids,
+};
+
+static int __init etm_init(void)
+{
+        int retval;
+
+        retval = amba_driver_register(&etb_driver);
+        if (retval) {
+                printk(KERN_ERR "Failed to register etb\n");
+                return retval;
+        }
+
+        retval = amba_driver_register(&etm_driver);
+        if (retval) {
+                amba_driver_unregister(&etb_driver);
+                printk(KERN_ERR "Failed to probe etm\n");
+                return retval;
+        }
+
+        /* not being able to install this handler is not fatal */
+        (void)register_sysrq_key('v', &sysrq_etm_op);
+
+        return 0;
+}
+
+device_initcall(etm_init);
+