coresight: etb10: Add support for CPU-wide trace scenarios

This patch adds support for CPU-wide trace scenarios by making sure that
only the sources monitoring the same process have access to a common sink.
Because the sink is shared between sources, the first source to use the
sink switches it on while the last one does the cleanup.  Any attempt to
modify the HW is overlooked for as long as more than one source is using
a sink.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Tested-by: Leo Yan <leo.yan@linaro.org>
Tested-by: Robert Walker <robert.walker@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hwtracing/coresight/coresight-etb10.c b/drivers/hwtracing/coresight/coresight-etb10.c
index eeae375c7aed0f5e78821738a470c57bca9d4652..4ee4c80a4354397871ca8cb7368050f2daa4e1df 100644 (file)
--- a/drivers/hwtracing/coresight/coresight-etb10.c
+++ b/drivers/hwtracing/coresight/coresight-etb10.c
@@ -72,6 +72,8 @@
  * @miscdev:   specifics to handle "/dev/xyz.etb" entry.
  * @spinlock:  only one at a time pls.
  * @reading:   synchronise user space access to etb buffer.
+ * @pid:       Process ID of the process being monitored by the session
+ *             that is using this component.
  * @buf:       area of memory where ETB buffer content gets sent.
  * @mode:      this ETB is being used.
  * @buffer_depth: size of @buf.
@@ -85,6 +87,7 @@ struct etb_drvdata {
        struct miscdevice       miscdev;
        spinlock_t              spinlock;
        local_t                 reading;
+       pid_t                   pid;
        u8                      *buf;
        u32                     mode;
        u32                     buffer_depth;
@@ -169,28 +172,49 @@ out:
 static int etb_enable_perf(struct coresight_device *csdev, void *data)
 {
        int ret = 0;
+       pid_t pid;
        unsigned long flags;
        struct etb_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
+       struct perf_output_handle *handle = data;
 
        spin_lock_irqsave(&drvdata->spinlock, flags);
 
-       /* No need to continue if the component is already in use. */
-       if (drvdata->mode != CS_MODE_DISABLED) {
+       /* No need to continue if the component is already in used by sysFS. */
+       if (drvdata->mode == CS_MODE_SYSFS) {
+               ret = -EBUSY;
+               goto out;
+       }
+
+       /* Get a handle on the pid of the process to monitor */
+       pid = task_pid_nr(handle->event->owner);
+
+       if (drvdata->pid != -1 && drvdata->pid != pid) {
                ret = -EBUSY;
                goto out;
        }
 
+       /*
+        * No HW configuration is needed if the sink is already in
+        * use for this session.
+        */
+       if (drvdata->pid == pid) {
+               atomic_inc(csdev->refcnt);
+               goto out;
+       }
+
        /*
         * We don't have an internal state to clean up if we fail to setup
         * the perf buffer. So we can perform the step before we turn the
         * ETB on and leave without cleaning up.
         */
-       ret = etb_set_buffer(csdev, (struct perf_output_handle *)data);
+       ret = etb_set_buffer(csdev, handle);
        if (ret)
                goto out;
 
        ret = etb_enable_hw(drvdata);
        if (!ret) {
+               /* Associate with monitored process. */
+               drvdata->pid = pid;
                drvdata->mode = CS_MODE_PERF;
                atomic_inc(csdev->refcnt);
        }
@@ -336,6 +360,8 @@ static int etb_disable(struct coresight_device *csdev)
        /* Complain if we (somehow) got out of sync */
        WARN_ON_ONCE(drvdata->mode == CS_MODE_DISABLED);
        etb_disable_hw(drvdata);
+       /* Dissociate from monitored process. */
+       drvdata->pid = -1;
        drvdata->mode = CS_MODE_DISABLED;
        spin_unlock_irqrestore(&drvdata->spinlock, flags);
 
@@ -406,7 +432,7 @@ static unsigned long etb_update_buffer(struct coresight_device *csdev,
        const u32 *barrier;
        u32 read_ptr, write_ptr, capacity;
        u32 status, read_data;
-       unsigned long offset, to_read, flags;
+       unsigned long offset, to_read = 0, flags;
        struct cs_buffers *buf = sink_config;
        struct etb_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 
@@ -416,6 +442,11 @@ static unsigned long etb_update_buffer(struct coresight_device *csdev,
        capacity = drvdata->buffer_depth * ETB_FRAME_SIZE_WORDS;
 
        spin_lock_irqsave(&drvdata->spinlock, flags);
+
+       /* Don't do anything if another tracer is using this sink */
+       if (atomic_read(csdev->refcnt) != 1)
+               goto out;
+
        __etb_disable_hw(drvdata);
        CS_UNLOCK(drvdata->base);
 
@@ -526,6 +557,7 @@ static unsigned long etb_update_buffer(struct coresight_device *csdev,
        }
        __etb_enable_hw(drvdata);
        CS_LOCK(drvdata->base);
+out:
        spin_unlock_irqrestore(&drvdata->spinlock, flags);
 
        return to_read;
@@ -733,6 +765,9 @@ static int etb_probe(struct amba_device *adev, const struct amba_id *id)
        if (!drvdata->buf)
                return -ENOMEM;
 
+       /* This device is not associated with a session */
+       drvdata->pid = -1;
+
        desc.type = CORESIGHT_DEV_TYPE_SINK;
        desc.subtype.sink_subtype = CORESIGHT_DEV_SUBTYPE_SINK_BUFFER;
        desc.ops = &etb_cs_ops;